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Law of Warfare

Rules of Engagement and Undersea Incursions: Reacting to Foreign Submarines in Territorial Waters

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This article is part of a series that will explore the use and legal issues surrounding military zones employed during peace and war to control the entry, exit, and activities of forces operating in these zones. These works build on the previous Maritime Operational Zones Manual published by the Stockton Center for International Law predecessor’s, the International Law Department, of the U.S. Naval War College. A new Maritime Operational Zones Manual is forthcoming.

By LtCol Brent Stricker

“We have attacked, fired upon, and dropped depth charges on a submarine operating in defensive sea area.”–USS Ward (DD-139) December 7, 1941, Pearl Harbor, Hawaii.

Submerged foreign submarines in a nation’s territorial sea pose a unique situation that is inconsistent with the rule of innocent passage. Under certain circumstances, their concealed presence without the consent of the coastal state could be considered a threat to the territorial integrity or political independence of the coastal state. A modern submarine fulfills its peacetime mission and combat role while submerged. If the coastal state detects a submerged submarine in the territorial sea, it is faced with a dilemma on the appropriate measures that can be used to force the submarine to surface or leave the territorial sea. The recent sabotage of the Nord Stream pipeline and the vulnerability of the world’s vast subsea network of electricity and network cables highlights the danger posed by unknown submersibles.

Norway and Sweden have faced this problem for more than 50 years from suspected Soviet and later Russian submarines. Both countries have used warning shots in an attempt to signal the submerged contacts to surface or leave the area. Use of explosives in this manner, however, could be misinterpreted as an attack on the submarine. Balancing the protection of territorial sovereignty with avoiding escalation poses a predicament.

Innocent Passage

All ships, including warships, enjoy the right of innocent passage through the territorial seas of a coastal state without prior notification or consent. This rule was discussed in detail in the Corfu Channel case before becoming codified in the United Nations Convention on the Law of the Sea. The Corfu Channel is a narrow passage between Albania and the Greek island of Corfu. The United Kingdom’s Royal Navy was confronted by Albanian coastal artillery fire when transiting the channel in May 1946. In October 1946, two Royal Navy destroyers transited the channel while at action stations to be prepared to respond to coastal artillery fire or other threat posed by the Albanians. These destroyers struck naval mines laid in the channel. As a result, in November 1946, the Royal Navy conducted minesweeping operations to clear the channel.

The United Kingdom brought a case against Albania in the International Court of Justice seeking reparations for the loss of life and damages to its warships. The ICJ upheld the Royal Navy’s right of innocent passage through Albanian territorial waters, rejecting Albania’s arguments that the ships were not in innocent passage because they were sailing in formation and the sailors on board were at action stations. Rather, the Court found that sailing in formation and running at action stations were appropriate defensive measures. The Court found that the minesweeping operation was inconsistent with innocent passage and a violation of Albanian sovereignty, rejecting the British arguments that this was a measure of “self-protection.” Corfu Channel illustrates how innocent passage may include defensive measures. The case has long presented a conundrum because it determined that states are entitled to innocent passage, yet are restrained from taking defensive action, such as minesweeping, to exercise their right.  

Innocent passage is governed by the United Nations Convention on the Law of the Sea (UNCLOS). Norway and Sweden are signatories to UNCLOS, and the United States, while not a signatory, recognizes much of it as customary international law. UNCLOS codified the right of innocent passage in Articles 17-21. Innocent passage must “not be prejudicial to the peace, good order, or security of the coastal state.” A foreign vessel’s passage is not innocent if its actions constitute “any threat or use of force against the sovereignty, territorial integrity or political independence of the coastal State.” A special provision for submarines, Article 20, requires submarines engaged in innocent passage to “navigate on the surface and to show their flag.”

A coastal state that discovers an unknown submerged contact in its territorial sea is faced with a dilemma. Examples from Norway and Sweden of submerged contacts lingering in their territorial waters are inconsistent with the definitions of both passage and innocent passage. The coastal state, under Article 25 of UNCLOS, may “take the necessary steps in its territorial sea to prevent passage which is not innocent.” There is no agreement on exactly what steps are deemed necessary. Furthermore, these measures are limited when applied to sovereign immune warships. Thus, while an unknown submerged contact is not exercising innocent passage, it is unclear what measures a coastal state can apply to exercise its rights under Article 25. Articles 30 and 31 of UNCLOS allow a coastal state to require the submerged contact to leave its territorial sea and places liability for any damages on the flag state of the submerged contact. Armed force against an unknown submerged contact, however, may only be used in self-defense under Article 51 of the UN Charter. In most cases, use of force would not be justified simply because the submarine is submerged or refuses to surface and the mere presence of the submarine does is not tantamount to an “armed attack.” This determination is complicated when the submerged contact’s intensions cannot be ascertained.

Norway

Norway has been dealing with suspected intrusions by foreign submarines for more than 50 years. These contacts in Norwegian fjords are difficult to track due to the mixing of fresh water runoff and salt water in the fjords which can provide cover for submarines from sonar detection. Acoustic detection is complicated by the fjord’s subsurface structure, currents, and civilian surface traffic. For two weeks in November 1972, Norwegian vessels aided by Norwegian and British aircraft attempted to locate and force to the surface an unknown underwater contact, believed to be of Soviet or Warsaw Pact origin, in the Sogne Fjord using depth charges. Hand grenades and then depth charges were used to signal to the underwater contact to surface. Ultimately, the Ministry of Defense was given permission to sink the contact if it did not surface and identify itself.

For the Norwegians to use force against the unknown submerged contact, they would need to articulate how an otherwise benign submerged vessel posed an imminent threat that would justify the use of force in self-defense. Violating Article 21 of UNCLOS in and of itself does not constitute such a threat of imminent attack, even if the submarine is engaged in an intelligence or reconnaissance mission. Such a mission may be illegal under Norway’s domestic law, but it does not imply an illegal use of force, let alone an armed attack.

In limited situations, the location and duration of the unknown submarine in territorial waters could be considered as a threat, as noted in the radio transmission of the USS Ward when it engaged an unknown submarine in a defensive sea area. The Norwegians would be more concerned by the location of the unknown submersible if it were in such an area or in close proximity to another sensitive military exercise or base. The longer the submarine remained at depth, the greater potential one might consider it laying in wait to attack. Nonetheless, the Norwegians employed an escalating use of force in 1972 with attempts to signal with hand grenades and ultimately culminating with firing anti-submarine missiles at the suspected target. The Norwegians were ultimately unable to force the contact to the surface, identify it, or sink it.

Norwegian experiences with unknown submarine contacts continued over the decades. The official Norwegian policy on the use of force remained somewhat ambiguous. In 1983, Brigadier Asbjorn V. Lerheim stated on the use of force, “It is a tough decision, it is still peacetime, and you can’t really destroy a submarine . . . it is not an attack on Norwegian soil.” Norway seems to have adopted a set of measures to escalate the use of force against these intrusions. The first measure is to signal the submarine to surface. If the submarine complies, it would be taken under escort. If not, depth charges would be dropped within 300 meters from the submarine with a two-minute interval to indicate this was a signaling measure, not an attack. If this failed to surface the submarine, Norwegian captains were authorized to attack with depth charges, but torpedoes were prohibited in the attack because of the potential of catastrophic damage to the boat and loss of the entire crew. It is speculated that the anti-submarine missiles fired in 1972 used homing devices and proximity fuses and were not a real attempt to hit the submarine.

Suspected Soviet incursions into Norwegian territorial waters continued as late as 1990. Norwegian authorities received reports of suspected submarines in the summer of 1990 at Skipton, a Norwegian bay twenty-five miles from the Russian border. The area was put under surveillance when, in November 1990, a mini-submarine was observed briefly on the surface. The sea floor was examined and a series of tracks were found that indicated a submersible crawler had been deployed. Similar tracks were discovered elsewhere in Sweden and Norway near military installations. The Soviet Northern Fleet possessed such miniature submarines at the time. It was speculated that the miniature submarine was launched from a nearby mother ship to conduct a Spetsnaz training or reconnaissance mission.

As late as 2021, Norway was subjected to an undersea intrusion by unknown submersibles. The Norwegian Institute of Marine Research operates a network of undersea sensors in northern Norway to monitor the marine environment. It can also be used to monitor submarines in the area. These sensors are interconnected by a series of fiber optic cables. In April 2021, it was discovered that 2.5 miles of fiber optic cable had been cut and stolen. Several of the sensors had been tampered with and moved. The reason for the intrusion is speculative but includes the potential for reverse engineering.

Sweden

Like Norway, Sweden has been troubled by intrusions of foreign submarines in its territorial waters for a similar period of time. Unlike Norway, Sweden has actually caught one submarine on the surface in the infamous “Whiskey on the Rocks” incident in 1981. This incident noted increased intrusions throughout the 1980s that have continued as late as the 2010s. To date, the Whiskey is the only foreign submarine caught on the surface in Swedish territorial waters.

On October 27, 1981, a Soviet Whiskey class submarine, the U-137, was found grounded on a rock in Swedish territorial waters. The Whiskey was an early Cold War diesel electric submarine, not a nuclear-powered submarine. The Swedish Navy contacted the submarine’s captain, Captain Second Rank A. M. Gushchin, who claimed a navigational error. Captain Gushchin claimed he thought he was 20 miles off the Polish coast when the collision occurred. This claim is rather dubious considering the submarine had transited submerged through a “perilous series of narrow straits infested with rocks and islands” before the grounding. The submarine’s grounding within ten kilometers of the Swedish naval base at Karlskrona while a major naval exercise was being conducted was certainly not just a coincidence brought about by a navigational error. Upon inspection, Swedish officials found no problems with the boat’s navigational equipment and noted its logbook had been altered.

The boat remained grounded for eleven days while the Swedish authorities inspected the submarine and questioned the captain. The Soviet Union responded by sending a flotilla of warships that stayed just outside Swedish waters. The Swedish Prime Minister made a shocking announcement on November 5, 1981, that the submarine was suspected of carrying nuclear weapons. The Swedish government made demands to the Soviets before releasing the submarine. However, weather intervened and Sweden released the submarine before these demands were met. The submarine was exposed to gale force winds and was listing 17 degrees. Swedish authorities were concerned that the boat’s battery acid could spill and cause a fire or release chlorine gas that could kill the crew. Swedish authorities stopped the captain’s interrogation and boat inspection, refloated the boat, and the submarine left on November 6, 1981.

Following this incident, the Swedish government released the Submarine Defense Commission Report in 1983, which detailed the history of foreign submarines intruding into Swedish waters. Prior to the Whiskey incident, and even subsequently, critics had claimed these submarine scares were an excuse to increase the Navy’s budget. The report detailed how foreign submarines entered Swedish waters typically one to two times a year in the 1970s before a dramatic increase during the 1980s. These incursions were concentrated around naval facilities such as coastal defense points, ports, sensor networks, and minefields.

The Report and increased submarine intrusions led to a change in Swedish Rules of Engagement (ROE) applicable to submarine contacts. Prior rules prohibited a commander from firing on an unknown contact without authorization from the civilian leadership. The Swedish Navy was only allowed to make contact with the submarine to identify it and escort it out of Swedish waters. The new ROE allowed the submarine to be fired upon without warning. Initially, warning shots were to be used, either through the employment of depth charges or missiles. The ROE were intended to prevent the damage or destruction of the submarine, but the ROE made a distinction on the location and behavior of the contact. If the submarine was located in Sweden’s outer waters, these are waters beyond the internal archipelago to the 12-mile limit, it would be warned and escorted out. If the submarine was found in internal waters, these are waters of Sweden’s internal archipelago, and refused to leave or proceeded further, it could be treated as hostile and force designed to damage or destroy the submarine could be used.

The Swedish ROE may have contributed to their inability to force submarines to the surface. If they employed depth charges or other devices with an eye toward avoiding damaging the detected submarines, the submarines could simply ignore these attempts. There is evidence that the Swedish ASW may have damaged a submarine. In the summer of 1988, eight pieces of unknown foreign submarine rescue equipment were recovered in the Stockholm archipelago. Similar equipment had been recovered in the 1970s and 80s.

The Swedish Navy continued to deal with foreign submarines intruding into Swedish waters throughout the 1980s. The government stopped providing statistics on these incursions in 1987. Subsequent reports have been vague in their descriptions. This may be to avoid highlighting their inability to stop or deter these incursions.

There is evidence that these incursions did occur. The Swedish Navy noted that these incursions have become more sophisticated with the use of multiple submarines, miniature submarines, and divers. The evidence for these incursions comes from sightings, sonar, and magnetic detection from Swedish sensor networks. There has also been evidence of keel marks and track marks on the sea floor similar to the Norwegian miniature submarine event noted above.

The miniature submarines may have also allowed military forces to surreptitiously land on Swedish territory. Between 3 to 6 March 1984, Swedish forces fired at swimmers on the island of Almo. The island was searched and food caches were located. The Swedes have also noted attacks on their “submarine nets, break-ins ashore, to the disruption and destruction of underwater mine lines.” In one case, they were blamed for the theft of a naval mine. Most shockingly, in 1985 fisherman pulled a drowned swimmer up in their nets. The nets had been placed illegally near a naval mine. It is presumed the diver was scouting the mine when he became entangled and drowned. The fisherman did not recover the body and abandoned their nets. When Swedish authorities investigated, the body had been cut out of the net and removed by unknown persons.

Conclusion

This historic submarine incursions remain relevant today, particularly considering heightened tensions from the Russian invasion of Ukraine and the recent application of Finland and Sweden to join the North Atlantic Treaty Organization. Much like the Norwegian fjords, the Swedish archipelago would be an area for these submarines to operate. The reasons for the incursions remain relevant today for any NATO-Russian conflict whether it be to conduct reconnaissance or the insertion of Special Forces. If there is a repeat of one of these Cold War examples such as a stranded submarine like the Whiskey, or more concerning, NATO forces hunting a submarine contact, the consequences could be manifold. First, NATO forces chasing a submarine contact trying to force it to surface might be viewed as an attack on the submarine. The use of explosives to signal a submarine might accidentally damage it or injure the crew. These signals could be misinterpreted as an attack allowing or even requiring a submarine to respond in self-defense. Second, any hostilities in territorial waters directly implicates the collective self-defense clause of Article 5 of the North Atlantic Treaty.

The conduct of Russian submarine espionage in the territorial seas of its neighbors presents one of the greatest challenges to avoiding conflict in the Baltic Sea. These incidents reveal the gap between the law of the sea and the use of force in self-defense against an armed attack. The Nordic coastal states must walk a fine line between protecting their territorial integrity and avoiding escalation of an incident that might quickly spin out of control.

LtCol Brent Stricker, U.S. Marine Corps, serves as the Director for Expeditionary Operations and as a military professor of international law at the Stockton Center for International Law, U.S. Naval War College. The views presented are those of the author and do not necessarily reflect the policy or position of the U.S. Marine Corps, the U.S. Navy, the Naval War College, or the Department of Defense.

Featured Image: Russian Kilo-class submarine in the English Channel. (UK Ministry of Defence photo via Wikimedia Commons)

Culture

Binary Submarine Culture? How the Loss of the USS Thresher Hastened the End of Diesel Submarine Culture

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By Ryan C. Walker

During my short tenure as a submariner in the U.S. Navy, from 2014-2019, I observed the friendly rivalry between sailors who serve on SSN (fast-attack boats), SSGN (frequently shortened to GN boats), and SSBN (Trident boats). Fast-attack sailors like to brag about port calls and joke that sailors on the other vessels are part-time sailors due to the Gold/Blue crew system. For their part, Trident and GN sailors generally have a higher quality of life. They rarely hot-rack, have a more predictable schedule and have more space for crew morale. As much as fast-attack sailors envy these benefits, they know, even if they don’t want to admit, our Trident and GN brethren earn their pay. They do spend extended periods on patrol, have fewer opportunities for port calls, and their time at sea is monotonous. Despite the variations between these subcultures within the submarine fleet, the nuclear culture that stresses safety through rigorous engineering, procedural compliance, and training is still the common bedrock of identity on all platforms.

Previously, two separate cultures existed within the submarine fleet, diesel and nuclear. This article will discuss how the USS Thresher tragedy on April 10, 1963 hastened the end of the binary approach and eventually led to the single bedrock foundation that submarine culture now rests on. The United States Navy’s Submarine Safety (SUBSAFE) Program is written in the blood of the 129 souls who died on the USS Thresher and remain on eternal patrol. Diesel submarine culture, epitomized by the slogan “Diesel Boats Forever,” would be replaced by the cold, calculating, and rigorous nuclear culture design by Hyman G. Rickover. Current proposals to reintroduce diesel submarines in the Navy’s fleet focus on fiscal and operational factors, but the potential risks to its submarine culture should also be considered. This article will examine how the two communities previously interacted as diesel submariners were forced to take on the extra burden of supporting a new technology while that same technology was replacing them. It will further offer that this is not inevitable, but should reintroduction proposals ever gain currency, the conversation on submarine culture should be a major topic by political and military leaders.

Documenting the Tragedy

The Thresher has an enduring effect on the mentality of the present-day submarine force, forming the basis for many training sessions and case studies. Publications, many from the past decade, reflect the memory of the Thresher is well. Many of these have a general focus, examining how and why the Thresher was lost,1 and how the Thresher disaster can serve as case studies for public affairs, oceanography and naval professionals.2 However, the publications examining how the Thresher disaster inspired changes in submarine culture, shipbuilding design, and SUBSAFE are of particular interest.3 James Geurts’ article in USNI Proceedings discusses how the loss profoundly impacted naval officer’s training, arguing procedures to fully employ the capabilities of nuclear-powered submarines only accelerated in the aftermath, stating the “Navy was still locked into training officers for duty on diesel-electric boats, even though the boats quickly were becoming obsolete.”4 Synthesizing these articles and connecting their arguments shows that the end of the binary submarine culture was a positive change overall.

Rickover, Nuclear Power and SUBSAFE

It is generally accepted that Hyman G. Rickover was the architect of nuclear submarine culture and the driving force for the quicker transition to nuclear culture by promulgating the practices, procedures, mentality and culture of as the standard for all submariners. As Geurts would summarize:

“Despite these demonstrations of superiority, the Navy’s operational thinking carried over from diesel-electric boats to the nuclear submarines. The distinction… was not yet recognized or emphasized during submarine school training. This fundamental failure in thinking contributed to the Thresher disaster, after which the Navy finally met the new reality of nuclear-powered submarines with fresh operational thinking.”5

How the evolution occurred still requires research. A common misperception of the ship’s status at its loss was that it was conducting its first deep dive. Following its commissioning the Thresher had undergone extensive testing, befitting its status as the first of her class. Built in Portsmouth Naval Shipyard in Kittery, ME, the ship completed all its acceptance trials, shakedown availability, and even participated in some fleet exercises.

It came as a complete surprise to all involved when it was lost with all hands, the ship’s former medical officer Arthur L. Rehme shared his experience onboard and that he felt confident in the crew, even sharing the first time they reached a record depth the ship cheered.6 The loss was truly unexpected, it is a testament to contemporary submarines that they were willing to persevere despite the loss. Crew member Ira Goldman, who narrowly avoided death by attending a training school, continued to serve in the submarine fleet, retiring as a Master Chief.7 Rehme did not continue as a submariner, but decided if the men on the Thresher could give their lives in service of their country, he too could continue to serve.8 Their loss served as an inspiration for change, but also an iron determination for those who faced the same risks.

Almost immediately, a Court of Inquiry was organized to discern why the Thresher sank, which canvassed a wide variety of persons. Obvious candidates such as the recently relieved commanding officer (CO), Dean L. Axene and watch standers on the Skylark were involved, but so too were people with only a passing military, technical or familial background. The Court concluded that the Thresher was lost due to flooding casualty from piping in the Engine Room that shorted out vital electrical equipment, a decision that would have consequence for construction, maintenance, and repair of new submarines. This recommendation was influenced by Rickover, who insisted on being interviewed by the Court of Inquiry. Instead of defending the nuclear program, he displayed his shrewd ability to identify problems in a now famous quote:

“I believe the loss of the THRESHER should not be viewed solely as the result of failure of a specific braze, weld, system or component, but rather should be considered a consequence of the philosophy of design, construction and inspection, that has been permitted in our naval shipbuilding programs. I think it is important that we re-evaluate our present practices where, in the desire to make advancements, we may have forsaken the fundamentals of good engineering.”9

It was no accident that he had insisted to be a witness. According to his biographer, Francis Duncan, he thought the testimony “could be an opportunity to show how the technical standards that he had insisted upon should be applied to other work.”10 Rickover came with the intent to promulgate what would become SUBSAFE, offering an immediate solution in the form of nuclear culture.

The shift may have happened over time as nuclear-trained officers with no experience on diesel submarines became the norm. The influence of the Rickover-designed training program is still evident from the admirals he trained down to junior officers learning the principles for the first time. The expectations established for nuclear trained enlisted personnel would also be expected in the forward compartment, or “cone.” While there is still a strong divide between “nukes” and “coners,” both groups have the mindset of engineering indoctrinated through training and qualifications. The disaster itself acted as a catalyst for change, alongside the Scorpion, to implement Rickoverian philosophy in the submarine fleet.

SUBSAFE is among the crowning administrative and engineering achievements of the USN. It became such a successful quality assurance program that other organizations looked to it for inspiration on their own programs. In the aftermath of the Challenger disaster, NASA was recommended to look “to two Navy submarine programs that have “strived for accident-free performance and have, by and large, achieved it – the Submarine Flooding Prevention and Recovery (SUBSAFE) and Naval Nuclear Propulsion (Naval Reactors) programs.”11 SUBSAFE is a body of practices that became a mindset and an essential building block of culture for the present submarine culture. It was no longer, as Geurts had stated succinctly, a diesel dominated fleet, but a nuclear fleet first and foremost, as reflected by Navy recruitment and informational topics by the period.12

The Origin of Diesel Boat Forever Culture: Diesels Boats Perform an Essential Transitional Duty

The delays in nuclear submarine construction and their lengthier overhaul periods, relative to diesel boats, would prove to have long-term consequences that are still present today. The immediate effect was to increase the costs and time periods construction and overhaul would consume. As a result, operational commitments often fell to diesel submarines as they took on the missions of the nuclear submarines stuck in overhaul. Even in the present day, overruns in cost and time are frequent and accounted for but are merited in the name of safety. Diesel boats would serve an important purpose during the early implementation of SUBSAFE in new construction, holding the line, but frequently forgotten in the public Cold War narrative of nuclear boats that seemed to get the attention as the future.

The Submarine Force Library and Museum archives carry the development of this culture epitomized by the Diesel Boat Forever (DBF) pin. The DBF pin was created by the crew of the USS Barbel, with an enlisted sailor Leon Figurido drawing it for a contest and adopted by the command, conflicting accounts offer 1967-1971 as the period they were made.13 The pin was explicitly designed as the answer to the Polaris Patrol Pin and inspired by the Submarine Combat Patrol Pin. Two bare chested mermaids clasping hands while laying over a submarine silhouette with the immortal acronym, “DBF” surrounded by holes for stars. According to Meagher, the former commanding officer (CO) who approved the project, John Renard, confirmed instead of receiving a star for each patrol, DBF pins would receive a star “each time a diesel boat you served on had to get underway for a broke-down nuke.”14 There was still a surprising amount of buy-in from diesel sailors in higher chains of command. The pin was unofficially condoned to the point that the CO of the Tigrone held a ceremony awarding RADM Oliver H. Perry jr., who had previously served on diesel boats.15 Smith in his interview with Adams also remarked other memorabilia, such as Red DBF Jackets were a part of the culture and sold out as soon as they were back from their deployment, reflecting an appeal for a new identity formed in the shadow of the new nuclear submarine culture.16

Unsurprisingly, this was greeted coolly by nuclear submariners. The animosity was shared, where Smith recalled fights that broke out “between the ‘nukes and the reds’ when they wore their jackets ashore.”17 This further indicates the budding nuclear culture was prideful enough to take offence at the “other” fleet. To fully illustrate the diesel culture of the submarine fleet, look no further than the 1996 film, Down Periscope. The film follows an unconventional Submarine Officer LCDR Dodge taking command of the decrepit diesel submarine, the USS Stingray. Manned by what can only be politely described as the dregs of the Navy, the Stingray crew embraces this mentality, performing unorthodox tactics and techniques throughout the film. The director elected to utilize a retired enginemen named Stanton, as the chief engineer. It is from him we hear the clear signaling of intent of the film when he yells at the climax of the film, “This is what I live for! DBF!”18

While never in doubt due to the subject of this film, the true intent of the film was illuminated in this moment. This pithy aphorism epitomizes the romanticized diesel sailor; a mythos that has not disappeared in the nuclear navy. The final, romanticized aspect of the film is fleshed out when Dodge rejects his promotion to command a new, nuclear powered Seawolf class submarine, opting instead to stay with the barely seaworthy, antiquated, hopelessly outmatched Stingray.19 In many respects, its origins lie in the hero worship of WWII submariners who did not need procedures and the high attention to safety paid in the modern Navy yet still brought the fight to the enemy and performed admirably. It is spoken in the same vein spoken by resentful sailors from the age of sail who viewed their younger generations in the age of steam as soft, jibing them comments such as “once the navy had wooden ships and men of iron; now it has iron ships and wooden men.”20 There is no doubt in anyone’s mind who has read the accounts from diesel sailors that it was an undoubtedly difficult life.21 Nuclear submarine crews are lucky by comparison, but submarine duty is rightfully still considered to be difficult in the present day.

For all intents and purposes, there were two distinct cultures within the submarine fleet, but principally from 1963-73, as diesel submarines were replaced. Throughout the 1970s Meagher recalled “scores of career electricians and engineman were forced to “surface” as there was no room for them on Rickover’s boats.”22 Smith agrees they knew that they were a “dying breed,” but also adds “we’re damn proud to be diesel boat sailors.”23 Eventually, the unofficial pin was banned, and midshipmen were kept from diesel boats from 1973 onward, with some rumors stating it was due to concerns midshipman were being indoctrinated into diesel culture.24 This was part of the transition to a nuclear dominant force as the tragedies of the Thresher and Scorpion helped accelerate it. Diesel submarines are an important part of submarine heritage that is talked about today. The last combat ready diesel submarines, Barbel, Blueback and Bonefish, were decommissioned between 1988-90, meaning the operational capacity of the submarine force has been exclusively nuclear for over thirty years and had been dominated by nuclear trained officers for decades before.25

Proposals to Adopt Diesel Boats in the Present Day

Thus, the expectations for all sailors, both in engineering and non-engineering realms, are dictated by the principles instilled in them by Rickover’s nuclear program. The USS Thresher disaster was the defining moment for both the submarine fleet and the U.S. Navy itself. It was decided in the immediate aftermath to pursue an ambitious program that would touch all aspects of submarine culture, in construction, maintenance, overhaul, training, and operations. It would make the trends set forth by Hyman G. Rickover the norm, not the exception. The Thresher disaster was the moment the US Navy reinvented itself to embrace the mentality to become the force it is today.

Despite the success of the nuclear force, discussions on adopting the diesel submarine have resurfaced. Proposals such as the award-winning essay written for USNI Proceedings by Ensigns Michael Walker and Austin Krusz are frequently published. “The U.S. Navy would do well to consider augmenting its current submarine force with quiet, inexpensive, and highly capable diesel-electric submarine.”26 The argument is based on the increasing capability of the diesel submarines, the high cost of maintaining nuclear submarines, and the merit of increased operational flexibility. These proposals have merit and are popular outside of naval professionals, the citations of Walker and Krusz reflect the wide scope of popular interest.27

A discussion not mentioned is a potential return to the binary culture separating diesel submarine crews and nuclear submarine crews. DBF culture formed as a resentful reaction to the nuclear submarine crews for simultaneously giving them a greater portion of work and threatening their role in the Cold War. SUBSAFE can be bedrock of identity for a potential diesel submarine culture in the USN, but the cultivation of such a culture must be carefully managed and planned. Diesel submariners require a different mindset, and it is likely they will create some of their own norms; the question must be asked: does the Navy want this outcome? Or does it value the ability of career submariners to move between platforms with similar cultures and mindsets without having to worry about what their previous hull had been?

Nor will there be any insight seen in foreign markets in terms of safety. There have been several high-profile diesel submarine disasters in recent years. The KRI Nanggala 402 in 2021, the ARA San Juan in 2017, and the PLAN Ming 361 in 2003 are among the most recent and well known. It would be a mistake to assume nuclear submarines in other nations are immune to this either. Conversely, no US submarines built using the rigorous requirements in SUBSAFE have been lost to any disaster. The safety record is impressive and is due to more than the processes and procedures, but the culture of the crews manning the boars. Submarine Officers, with the exception of the supply officer, are engineers first and the mindset instilled in them would be instilled in their crews and stands as the legacy of the Thresher disaster and SUBSAFE programs.

Ryan C. Walker served in the USN from 2014-2019, as an enlisted Fire Control Technician aboard the USS Springfield (SSN-761). Honorably discharged in December of 2019; he graduated Summa Cum Laude from Southern New Hampshire University with a BA in Military History. He is currently a MA Candidate at the University of Portsmouth, where he studies Naval History and hopes to pursue further studies after graduation. His current research focus is on early submarine culture (1900-1940), early development of Groton as a Naval-Capital Town, and British private men-of-war in the North Atlantic. He currently resides in lovely Groton, CT.

Endnotes

1. See: Norman Polmar, The death of the USS Thresher: The story behind history’s deadliest submarine disaster. (Guilford: Rowman & Littlefield, 2004); James B. Bryant “Declassify the Thresher Data,” Proceedings, Vol. 144, (July 2018). https://www.usni.org/magazines/proceedings/2018/july/declassify-thresher-data; Jim Bryant, “What Did the Thresher Disaster Court of Inquiry Find?” Proceedings, Vol. 147, (August 2021), https://www.usni.org/magazines/proceedings/2021/august/what-did-thresher-disaster-court-inquiry-find; Dan Rather, “The Legacy of the Thresher,” CBS Reports, Television Film Media digitized on YouTube, originally aired March 4, 1964. Accessed April 22, 2022, https://www.youtube.com/watch?v=8aZ4udTMlZI

2. See: Robert J. Hurley “Bathymetric Data from the Search for USS” Thresher”.” The International Hydrographic Review (1964); Frank A. Andrews “Search Operations in the Thresher Area 1964 Section I.” Naval Engineers Journal 77, no. 4 (1965): 549-561; Joseph William Stierman jr., “Public relations aspects of a major disaster: a case study of the loss of USS Thresher.” MA Dissertation, Boston University, 1964.

3. See: James R. Geurts, “Reflections on the Loss of the Thresher,” Proceedings, Vol. 146, (October 2020), https://www.usni.org/magazines/proceedings/2020/october/reflections-loss-thresher; Michael Jabaley, “The Pillars of Submarine Safety,” Proceedings, Vol. 140, (June 2014), https://www.usni.org/magazines/proceedings/2014/june/pillars-submarine-safety; Joseph F. Yurso, “Unraveling the Thresher’s Story,” Proceedings, Vol. 143, (October 2017), https://www.usni.org/magazines/proceedings/2017/october/unraveling-threshers-story

4. James R. Geurts, “Reflections on the Loss of the Thresher,” Proceedings, Vol. 146, (October 2020), https://www.usni.org/magazines/proceedings/2020/october/reflections-loss-thresher

5. Geurts, “Reflections,” Proceedings

6. Arthur L. Rehme Collection, (AFC/2001/001/37677), Veterans History Project, American Folklife Center, Library of Congress, accessed April 24, 2022. https://memory.loc.gov/diglib/vhp/bib/loc.natlib.afc2001001.37677

7. Jennifer McDermott, “50 years later, Thresher veteran still grieves loss of shipmates at sea,” The Day, Waterford, April 5, 2013, 12:52PM, https://www.theday.com/article/20130405/NWS09/304059935

8. Arthur L. Rehme Collection, (AFC/2001/001/37677), Veterans History Project, American Folklife Center, Library of Congress, accessed April, 24 2022. https://memory.loc.gov/diglib/vhp/bib/loc.natlib.afc2001001.37677

9. Francis Duncan. Rickover: The struggle for excellence. (Lexington: Plunkett Lake Press, 2001). 85

10. Francis Duncan, Rickover, 81

11. Malina Brown. “Navy group to observe NASA’s return-to-flight activity: COLUMBIA ACCIDENT REPORT CITES SUB PROGRAMS AS MODEL FOR NASA.” Inside the Navy 16, no. 35 (2003): 12-13. Accessed December 8, 2020. http://www.jstor.org/stable/24830339.12-13

12. Periscope Films, “1965 U.S. NAVY NUCLEAR SUBMARINE RECRUITING FILM ‘ADVENTURE IN INNER SPACE’ 82444.” Accessed June 26, 2022, https://www.youtube.com/watch?v=RdgIqhf6FOY; Periscope Films, “U.S. NAVY NUCLEAR SUBMARINES MISSIONS, CHARACTERISTICS AND BACKGROUND 74802,” Accessed June 26, 2022, https://www.youtube.com/watch?v=d9ftfhiUMzY

13. Cindy Adams. “Barracks COB favors fossil fuels: ‘Diesel boats are forever,” The Day, November 14, 1980, Newspaper Clipping, Submarine Force Library and Museum, Submarine Archives, Uniforms & Insignia Collection; Stu Taylor, “The following story is about the origin of the DIESEL BOATS FOREVER emblem.” Submarine Force Library and Museum, Submarine Archives, Uniforms & Insignia Collection; Patrick Meagher. “THE DBF PIN.” Accessed May 22, 2022, http://www.submarinesailor.com/history/dbfpin/dbfpin.asp

14. Patrick Meagher. “THE DBF PIN.” Accessed May 22, 2022, http://www.submarinesailor.com/history/dbfpin/dbfpin.asp

15. Meagher, “DBF PIN,” Website

16. Cindy Adams. “Barracks COB favors fossil fuels: ‘Diesel boats are forever,” The Day, November 14, 1980, Newspaper Clipping, Submarine Force Library and Museum, Submarine Archives, Uniforms & Insignia Collection

17. Adams, “Barracks COB,” Newspaper Clipping.

18. Down Periscope, Directed by David S. Ward, (20th Century Fox, 1996), 1:19:00.

19. Down Periscope, 1:24:00 to 1:26:00

20. Baynham, H. W. F. “A SEAMAN IN HMS LEANDER, 1863–66.” The Mariner’s Mirror 51, no. 4 (1965), https://www.tandfonline.com/doi/abs/10.1080/00253359.1965.10657847?journalCode=rmir20, 343

21. Mark K. Roberts, SUB: an oral history of US Navy submarines. (New York: Berkley Caliber, 2007); Paul Stillwell. Submarine Stories: Recollections from the Diesel Boats. (Annapolis: Naval Institute Press, 2013); Claude C. Conner, Nothing Friendly in the Vicinity: My Patrols on the submarine USS Guardfish during WWII. (Annapolis: Naval Institute Press, 1999).

22. Meagher, “DBF PIN,” Website

23. Adams, “Barracks COB,” Newspaper Clipping.

24. Meagher, “DBF PIN,” Website

25. Honorable mention to the Darter and the Dolphin, both used for auxiliary purposes as well, decommissioned in 1990 and 2007 respectively.

26. Ensigns Walker & Krusz. “There’s a Case for Diesels.” Proceedings, Vol 144, (June 2018). Accessed August 25, 2021. https://www.usni.org/magazines/proceedings/2018/june/theres-case-diesels

27. See: James Holmes, Doug Bandow, and Robert E. Kelly, “One Way the U.S. Navy Could Take on China: Diesel Submarines,” The National Interest, 17 March 2017; Jonathan O’Callaghan, “Death of the Nuclear Submarine? Huge Diesel-Electric Vessel Could Replace Other Subs Thanks to Its Stealth and Efficiency,” Daily Mail Online, 4 November 2014; Sebastien Roblin, James Holmes, Doug Bandow, and Robert E. Kelly, “Did Sweden Make America’s Nuclear Submarines Obsolete?” The National Interest, 30 December 2016; Vego Milan, “The Right Submarine for Lurking in the Littorals,” U.S. Naval Institute Proceedings, 137, no. 6, June 2010, www.usni.org/magazines/proceedings/2010-06/right-submarine-lurking-littorals.

Featured Image: Port bow aerial view of USS Thresher, taken while the submarine was underway on 30 April 1961. (Photographed by J.L. Snell. Official U.S. Navy Photograph, from the collections of the Naval History and Heritage Command)

Drones/Unmanned

Manning the Unmanned Systems of SSN(X)

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By LCDR James Landreth, USN, and LT Andrew Pfau, USN

In Forging the Apex Predator, we published the results of a new analytical model that defined the limitations and constraints for the United States Navy’s Next Generation Attack Submarine (SSN(X)) concept of operations (CONOPS) for coordinating multiple unmanned undersea vehicles (UUV). Using a Model Based Systems Engineering approach, we studied tradeoffs associated with the number of UUVs, crew complement and UUV crew work schedule. The first iteration of our analysis identified crew complement as the limiting factor in multi-UUV, or “swarm,” operations. Identifying ways to maximize UUV operations with the small footprint crew required aboard submarines is critical to future SSN(X) design. Not all potential UUV missions require continuous human operator involvement. Seafloor surveys, mine detection, and passive undersea cable monitoring for ships can all occur largely independent of human supervision. The damage to Norwegian undersea cables in late 2021, potentially caused by a UUV, hints at the critical nature of this capability for 21st century conflict.1 By identifying operations that require less human supervision, CONOPs for SSN(X) can be tailored to maximize crew and UUV employment. The requirements for training and manning the crews to employ UUVs must be part of the considerations of creating the SSN(X) program.

The submarine force needs sailors with specialized skills to maintain, operate and integrate UUVs into SSN(X) operations. Because the submarine force and the United States Navy at large lack a documented, repeatable, and formalized process for training UUV operators and maintainers, the qualitative concept and computational model presented in this article offers a bridge to scaling multi-UUV operations. The Navy needs to develop codified training and manning requirements for UUV operations and the infrastructure, both physical and intellectual, to support unmanned systems operations. The recommendations discussed here are focused on the specific use case of UUVs deployed from manned submarines.

Defining the Human Operator’s Role in “The Loop”

In order to define a strategy to man SSN(X)’s UUV mission, the submarine force must first define the possible operational and maintenance relationships between man-unmanned teams. Once the desired relationships are defined, then the relevant activities can be listed and manpower estimates can be made for each SSN(X) and for the entire fleet. The importance of this definition and the resultant estimates cannot be understated. For example, launch and recovery of a medium UUV may be seen as consistent with existing Navy Enlisted Classifications (NECs) currently required in torpedo rooms across the fleet. Novel functions like “coordination of autonomous UUV swarms” has many supporting tasks that the Navy’s education enterprise is not yet resourced to meet. Identification of the human tasks required to meet the concept of operations (CONOP) is an essential component of integrated design for SSN(X).

The original model optimized five primary variables with a number of trial configurations, and found the most critical component for maximizing the battle efficiency of SSN(X)’s UUVs was crew support. Specifically, the model identified that the human resources consumed per UUV was the limiting relationship for the UUV swarm size deployable from a single hull. The first version of the trade study varied (a) the number of UUV crews available to support UUV operations and (b) the duration of these shifts, and used a human-in-the-loop configuration, which established a 1:1 relationship between crew and UUV. In order to employ multiple UUVs at once, the model consumed additional UUV crews for each UUV operating and/or increased the length of UUV crew’s shift. This manpower intensive model quickly constrained the number of UUVs that a single hull could employ at once.

Informed by the limitations that human resources placed on SSN(X)’s UUV mission, we updated the systems model to inform the critical task of “manning the unmanned systems.” Submariners and those who support their operations know the premium placed on each additional person inside the pressure hull. Additional crew members can limit the duration of a mission whether by food consumption, bed space, or breathing too much oxygen. As a result, any CONOP that adds a significant human compliment inside the skin of SSN(X) is likely to founder. Additionally, personnel operating and maintaining the UUVs will have a specific set of training, proficiency and career pathway requirements, whose cost will scale with the complexity of the UUV system and CONOP.

The original model was based on unmanned aerial systems (UAVs) operations and followed the manning concept of Group 5 UAVs, where one pilot is consumed continuously by an armed drone. Significant differences in operating environments between UAVs and UUVs necessitate different operating models. Due to the rapid attenuation of light and electronic signals in the undersea domain, data exchange between platforms occurs at relatively low speeds over comparatively limited distances unless connected by wire. This means that the global continuous command, control and communication CONOP available to UAVs will not transfer to UUVs. Instead, SSN(X) UUV operators will control their UUVs during operations relatively close to their manned platform, where the mothership and UUVs will share the same water space during launch and recovery. Communications at longer range will occur less frequently and be status updates to the operator rather than continuous or detailed. Separating the concern about counter detection and interception of acoustic signals, communications at range is possible.2

The unique physical characteristics of the underwater domain make communications one of the most challenging aspects of multi-UUV operations.

Putting connectivity differences aside, the manpower required for this human-in-the-loop model is unnecessarily limiting for the expected UUV CONOP. Alternate models are presented in Autonomous Horizons: The Way Forward, which details the roles for three man-machine team concepts: human-in-the-loop, human-on-the-loop and human-out-of-the-loop. A human-on-the-loop scenario would allow an operator to supervise a coordinated swarm rather than a single asset. This would be less efficient than fully autonomous operation, but dramatically improve the number of UUVs a SSN(X) could deploy as a swarm. Operations performed in this control mode would be limited to those that do not present a hazard to humans but require careful supervision such as a coordinated offensive search or scanning a mine field. Finally, a human-out-of-the-loop scenario would require the fewest human resources and maximize the number of UUVs an SSN(X) could effectively employ, but its mission scope is assumed to be limited to non-kinetic activities (“shaping operations”). Figure 1 provides a visualization of how mission role and levels of autonomy impact human resource requirements.

Given the multi-mission role that SSN(X) and its UUV swarm will play, the updated model offers three man-machine team configurations that could be matched to given missions. SSN(X) requirements officers, submarine mission planners and submarine community managers must understand these man-machine configurations in order to inform SSN(X)’s human resource strategy:

  1. In-the-Loop. The authors assumed that certain missions such as weapons engagement will continue to require a human-in-the-loop architecture where a human is continuously supervising or controlling the actions of a given UUV. As such, the original model results were retained to represent these activities and provide a baseline for comparison against the two other architectures.
  2. On-the-Loop. Directed missions like coordinated search or enemy tracking that could be precursors to human-in-the-loop scenarios benefit from the supervision of a human operator. In a human-on-the-loop architecture, the UUV operator is collaborating with one or more UUVs. The UUVs operate with a degree of autonomy and prompt the operator when they require human direction. The study assumed each operator could coordinate up to 3 UUVs, though this number is a first approximation. Further experimentation might show that this number could be significantly larger.
  3. Out-of-the-Loop. In this architecture, the UUV(s) engage in fully autonomous activities. They remain receptive to commands from the operator but require no input to perform their assigned role. The study assumed that an operator could coordinate up to 18 UUVs in a fully autonomous mode.3 However, this could scale as a multiple if SSN(X) could perform simultaneous launch and recovery operations from multiple ocean interfaces.

By affording the model the scale available from on-the-loop and out-of-the-loop control modes, the predicted swarm of UUVs could easily triple the area surveyed in a 24-hour period. Detailed results of the updated model are provided in Appendix 1. The submarine force must first consider its need to generate UUV crews for SSN(X), regardless of their mode of operation. More complex UUV operations will require greater skill investment, and more actively used UUVs per hull will impose a greater maintenance burden on the crew. Figure 1 illustrates the important relationship between UUV complexity, control mode, mission role across the range of military operations.

Figure 1. Man-Machine Teaming Based on Mission Role

Current Situation Report

The Navy’s guiding document for unmanned systems, the Unmanned Campaign Framework (UCF), addresses how Type Commanders will “equip” the fleet, but the Navy should expand the UCF to include how Type Commanders will perform their “man and train” missions.4 The realities of unmanned technologies will require new training for existing rates and potentially new specialized ratings. The “man and train” demand signals will become louder as the skills required for UUV operations and maintenance grow as a function of UUV complexity5 and scale6 of operations. Establishing a central schoolhouse and formal curriculum for officer and enlisted UUV skills is a strategic imperative. As a reminder, SSN(X)’s requirements demand complex UUV operations at scale.

The Navy has organized UUVs into four primary groups based on size. Figure 2 shows the categorization of UUVs into small, medium, large and extra-large UUV (SUUV, MUUV, LUUV, and XLUUV). The current groupings are based on the ocean interface required to deploy each UUV, but as the Navy develops its UUV CONOP, the submarine force would be wise to borrow from the similar categorization of unmanned aerial vehicles (UAV) in the Joint Unmanned Aircraft Systems Minimum Training Standards.7 The five UAV groupings consider not only physical size, mission, and operational envelop but also the qualification level required of the operators. These categories will determine how each UUV category will be employed, with SUUV, MUUV and even some LUUVs able to be deployed from manned submarine motherships. The complexity and skill required to operate UUVs will also scale with size, with larger UUVs able to carry more sensors at greater endurance. These categorizations easily translate into training and manpower requirements for operations, with more training and personnel required for larger UUVs.

Figure 2: UUV System Categorization by PMS 406. Click to expand.8

Almost all of the platforms illustrated in Figure2 are currently in the experimental phase, with only a few copies of each UUV platform available for test and evaluation. At least one UUV platform, the Knifefish, is moving into low-rate initial production.9 As the Navy moves to acquire more UUVs, it will have to transition its training of sailors from an ad hoc deployment specific training to codified schoolhouses.

In line with the experimental nature of current UUVs, the units that operate and maintain UUV systems also exist in the early phases. The Unmanned Undersea Vehicle Squadron 1 (UUVRON 1), and Surface Development Squadron 1 (SURFDEVRON 1) are tasked with testing unmanned systems and developing tactics, techniques, and procedures for their operation. Task Force 59, operating in the 5th Fleet area, is the first operational Navy command that seeks to work across communities to bring unmanned assets together for testing and operations. Sailors assigned to these commands will learn many unmanned-specific skills and knowledge on the job because the skills they bring from their fleet assignments may or may not be applicable. Similar to the schoolhouse challenge, establishing maintenance centers of excellence and expanding the work of development squadrons are essential pillars of the unmanned manpower strategy.10

Preparing for the Future

The Navy must train sailors for two primary UUV tasks: operations and maintenance. While the same sailor may be trained and capable of performing both tasks on UUVs, manpower models must accommodate enough personnel to simultaneously operate UUVs while performing maintenance on one or more other UUVs.

The submarine force can examine the operational training models that exists for UAVs where the size and capabilities of the UAV determine training requirements. The Department of the Navy already provides training for a range of UAV classes and missions including: RQ-21 Blackjack, ScanEagle, MQ-4 Triton, MQ-8C Fire Scout, and a number of other joint programs of record. The UAV training requirements exist in various stages of maturity, but on average exceed UUVs by several years or even decades due to early investment by both military and civilian organizations like the Federal Aviation Administration. Requirements for UAV training vary widely based on grouping. Qualification timelines for Group 1 UAVs like small quadcopters can be measured in days. Weapons-carrying or advanced UAVs like the MQ-9 Reaper require operators who have received years of training similar to manned aircraft pilots.

The Navy, Army and Marine Corps have established military occupational designations for roles related to UAVs, including maintenance and flight operations. They have established training courses to certify service operators and maintainers for a wide variety of UAV platforms. In contrast, the Navy has yet to promulgate a plan for Navy Enlisted Classifications (NEC) or Officer Additional Qualification Designations (AQD) or establish an equivalent career field for UUV operations at a level of detail consistent with legacy warfare platforms.

In addition to evaluating the transferability of lessons learned from the UAV community, the submarine force should incorporate the lessons learned from sister UUV users in the special warfare and explosive ordinance disposal domains. These communities possess the mature UUV technology and operating procedures. The experience of these communities can accelerate the nascent domain knowledge the submarine force has already established as it builds a foundation for multi-UUV operations from SSN(X). Separate from operations, the Navy will need to be able to perform organic-level maintenance tasks on UUVs at sea such as replacing circuit cards, swapping sensor packages, or maintaining propulsion units. Given SSN(X)’s heavy weapons payload requirements, an unmaintained UUV occupying a weapon’s stow will limit its intended multi-mission nature. The Navy will need to train its work force for these maintenance tasks. Just as importantly, UUVs will have to be designed for maintainability, so that basic components can be repaired or replaced at sea.

Manpower Models

However the Navy chooses to train sailors to operate and maintain UUVs, community managers will face a different set of choices when it comes to the organization and manning. There are two different models the Navy primarily uses to organize and man similar units supporting unmanned operations: directly assign sailors with the required skills to operational units or create specialized UUV detachments located in major homeports that then augment deploying units.

The most integrated model would be direct manning of submarines with sailors possessing the NEC or AQD certifying skill in operation and maintenance of UUVs. Each unit would have the number of billets necessary to meet manpower requirements and these sailors would be part of the crew, getting underway and performing duties other than those directly related to UUVs, even when UUVs are not onboard. This model would ensure continuous integration of UUV experts with the rest of the crew. While the crew may gain more knowledge from these experts, the experts may face challenges maintaining their expertise based on the needs of a given deployment. The most significant challenge to maintaining skills will be the availability of UUVs on every submarine and time at sea to practice operations.

The detachment model offers an arguably more proficient set of operators to a deploying unit, but can cause secondary impacts to warfighting culture. The Information Warfare Community (IWC) efficiently supports current submarine operations via the detachment model for certain technical operations. IWC “riders” are welcome compliments for important missions, but the augment nature means that the hosting submarine does not necessarily fully integrate the “rider’s” culture and knowledge into its own. If the submarine force adopted this model, a UUVRON at fleet concentration areas like Groton or Pearl Harbor would have administrative responsibility for sailors with the technical skills to maintain and operate UUVs. These sailors form into detachments and deploy to submarines to conduct operations while deployed. This model requires fewer personnel than a direct manning model, and these sailors will likely become more proficient in UUV operations. However, the rest of the submarine crew (and thus the force as a whole) would become less familiar with UUV operations without a permanent presence of expert sailors.

Both of the direct assignment and detachment manning models have advantages and drawbacks. Quantitatively, the submarine force must assign priorities and human resource availability to the variables within the trade space. Qualitatively, the Navy must determine how tightly UUV operators will be coupled to deploying units, and whether the detachment model can establish the desired UUV culture across the fleet.

Conclusion

Despite the unmanned moniker, UUVs will still require skilled humans to maintain and operate them. SSN(X) requirements officers, mission planners and community managers must provide early input into the types of autonomous missions SSN(X) UUVs will perform and the corresponding skill level required of sailors. To succeed, decision makers can compare the model provided in this article with existing programs of record’s training and certification requirements for UAVs. The submarine force must adopt a framework of training requirements that scales to UUV size and capability, and that framework must include whether UUV sailors will come from specialized detachments like current-day IWC riders or be integrated members of the crew. As the Navy moves UUVs from the test and evaluation to deployment phases and formalizes requirements for SSN(X), skilled sailors must be already in the fleet, ready to receive and operate these systems.

Lieutenant Commander James Landreth, P.E., is a submarine officer in the Navy Reserves and a civilian acquisition professional for the Department of the Navy. He is a graduate of the U.S. Naval Academy (B.S.) and the University of South Carolina (M.Eng.). The views and opinions expressed here are his own.

Lieutenant Andrew Pfau, USN, is a submariner serving as an instructor at the U.S. Naval Academy. He is a graduate of the Naval Postgraduate School and the U. S. Naval Academy. The views and opinions expressed here are his own.

Appendix 1: Data Comparison between System Optimized for Human-In-the-Loop versus On-the-Loop and Out-of-the-Loop Optima

 

# UUV # Crew Miles Scanned per 24 hrs Utilization
8 4 240 0.25
7 4 240 0.29
6 4 240 0.33
5 4 240 0.4
4 4 240 0.5
3 4 240 0.67
2 3 165 0.69

Table 5. Sample Analysis Results Optimized for Man-in-the-Loop (1:1)

 

# UUV # Crew Crew OPTEMPO UUV Charging Bays Charges per Day Miles Scanned per 24 hrs Utilization Notes ↑↓
8 4 0.5 2 0.33 659 0.69 2.75x ↑ in miles scanned; 2.76x ↑ in utilization
7 4 0.5 2 0.33 577 0.69 2.4x ↑ in miles scanned; 2.37x ↑ in utilization
6 4 0.5 2 0.33 494 0.69 2.06x ↑ in miles scanned; 2.1x ↑ in utilization
5 4 0.5 2 0.33 412 0.69 1.72x ↑ in miles scanned; 1.7x ↑ in utilization
4 4 0.5 2 0.33 330 0.69 1.72x ↑ in miles scanned; 1.7x ↑ in utilization
3 4 0.5 2 0.33 247 0.69 1.03x ↑ in miles scanned; 1.03x ↑ in utilization
2 3 0.5 2 0.33 165 0.69 No change

Table 6. Sample Analysis Results for On-the-Loop (3:1) vs Man-in-the-Loop Optima

# UUV # Crew Crew OPTEMPO UUV Charging Bays Charges per Day Miles Scanned per 24 hrs Utilization Notes
8 4 0.5 2 0.33 659 0.69 No change
7 4 0.5 2 0.33 577 0.69 No change
6 3 0.5 2 0.33 494 0.69 Same output with 1 fewer crew
5 3 0.5 2 0.33 412 0.69 Same output with 1 fewer crew
4 2 0.5 2 0.33 330 0.69 Same output with 2 fewer crew
3 2 0.5 2 0.33 247 0.69 Same output with 2 fewer crew
2 2 0.5 2 0.33 165 0.69 Same output with 1 fewer crew

Table 7. Sample Analysis Results for On-the-Loop (3:1) Re-Optimized

 

# UUV # Crew Miles Scanned per 24 hrs Utilization
8 4 659 0.69
7 4 577 0.69
6 4 494 0.69
5 4 412 0.69
4 4 330 0.69
3 4 247 0.69
2 3 165 0.69
8 2 659 0.69
7 2 577 0.69
6 2 494 0.69
5 2 412 0.69
4 2 330 0.69
3 2 247 0.69
2 2 165 0.69

Table 8. Sample Analysis Results for Out-Of-the-Loop (18:1) vs In-the-Loop Optimal. The same performance metrics of miles scanned and utilization rates are achieved with only 2 crews for the same UUV configurations.

Appendix 2: Analysis Constraint Equations

The following equations were used to develop a reusable parametric model. The model was developed in Cameo Systems Modeler version 19.0 Service Pack 3 with ParaMagic 18.0 using the Systems Modeling Language (SysML). The model was coupled with Matlab 2021a via the Symbolic Math Toolkit plug-in. This model is available to share with interested U.S. Government parties via any XMI compatible modeling environment.

Equation 7b. Crew Availability Equation introduces a new variable called “Number of UUV Managed per Crew.” This variable represents an evolution from the first version of this study, which limited an individual crew and its UUV to a 1:1 relationship. Equation 7a. Crew Availability Equation used in the first version calculations is included for comparison.

Equation 1. Scanning Equation

Equation 2. System Availability Equation

Equation 3. UUV Availability Equation

Equation 4. UUV Duty Cycle Equation

Equation 5. Day Sensor Availability Equation

Equation 6. Night Sensor Availability Equation

Equation 7a. Crew Availability Equation

Equation 7b. Crew Availability Equation

Equation 8. Charge Availability Equation

Equation 9. Utilization Score

Endnotes

1. Thomas Newdick, “Undersea Cable Connecting Norway with Arctic Satellite Station has been Mysteriously Severed”, The War Zone, Jan 10, 2022, online: https://www.thedrive.com/the-war-zone/43828/undersea-cable-connecting-norway-with-arctic-satellite-station-has-been-mysteriously-severed

2. Milica Stojanovic, “On the Relationship Between Capacity and Distance in Underwater Acoustic Communication Channel”, ACM SIGMOBILE Mobile Computing and Communications Review, Vol 11, Issue 4, Oct 2007. Online: https://doi.org/10.1145/1347364.1347373

3. The basis for 18 was that the deployment and recovery of each UUV would consume approximately 4 hours in an anticipated 72-hour UUV mission (72:4 reduces to 18:1).

4. Department of the Navy, “Unmanned Campaign Framework,” Washington, D.C., March, 2021 https://www.navy.mil/Portals/1/Strategic/20210315%20Unmanned%20Campaign_Final_LowRes.pdf?ver=LtCZ-BPlWki6vCBTdgtDMA%3D%3D

5. Complexity refers to the technical sophistication of each UUV and/or the difficulty of executing a mission within a realistic battle space

6. Scale refers to the number of UUVs in a coordinated UUV operation

7. Joint Staff, “Joint Unmanned Aircraft Systems Minimum Training Standards (CJCSI 3255.01, CH1),” Washington, D.C., September 2012

8. Slide 2 of briefing by Captain Pete Small, Program Manager, Unmanned Maritime Systems (PMS 406), entitled “Unmanned Maritime Systems Update,” January 15, 2019, accessed Oct 22, 2021, at https://www.navsea.navy.mil/Portals/103/Documents/Exhibits/SNA2019/UnmannedMaritimeSys-Small.pdf?ver=

9. Edward Lundquist, “General Dynamics Moves Knifefish Production to New UUV Center of Excellence,” Seapower Magazine, August 19, 2021, https://seapowermagazine.org/general-dynamics-moves-knifefish-production-to-new-uuv-center-of-excellence/

10. The end of 2021 saw initial operating capability for Task Force 59 in the 5th Fleet area of operations, which was the first unmanned Task Force of its kind.

Featured Image: BEAUFORT SEA, Arctic Circle (March 5, 2022) – Virginia-class attack submarine USS Illinois (SSN 786) surfaces in the Beaufort Sea March 5, 2022, kicking off Ice Exercise (ICEX) 2022. (U.S. Navy photo by Mike Demello)

Capability Analysis

Forging the Apex Predator:­­­ Unmanned Systems and SSN(X)

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By LCDR James Landreth, USN, and LT Andrew Pfau, USN

2041: USS Fluckey (SSN 812) Somewhere West of the Luzon Strait

Like wolves stalking in the night, the pack of autonomous unmanned underwater vehicles (UUV) silently swam from USS Fluckey’s open torpedo tubes. In honor of its namesake, “The Galloping Ghost of the China Coast,” Fluckey silently hunted its prey. With the ability to command and control an integrated UUV swarm via underwater wireless communication systems, Fluckey could triangulate any contact in the 160-mile gap between Luzon and Taiwan while maintaining the mothership in a passive sonar posture. Its magazine of 50 weapon stows brimmed with MK-48 Mod 8 Torpedoes. 28 Maritime Strike Tomahawks glowed in the vertical launch system’s belly like dragon’s fire. With just one hull, the Galloping Ghost sealed the widest exit from the South China Sea. Any ship seeking passage would have to pass through the jaws of the Apex Predator of the undersea.

Introduction

The Navy has its eyes set on the future of submarine warfare with the Next Generation Attack Submarine (SSN(X)), the follow-on to the Virginia-class attack submarine. Though SSN(X) has yet to be named, the Navy began funding requirements, development, and design in 2020. Vice Admiral Houston, Commander of Naval Submarine Forces, described SSN(X) in July 2021 as, “[T]he ultimate Apex Predator for the maritime domain.”1 In order to become the “Apex Predator” of the 21st century, SSN(X) will need to be armed not only with advanced torpedoes, land-attack and anti-ship cruise missiles, but also with an array of unmanned systems. While SSN(X) will carry both unmanned aircraft and unmanned undersea vehicles (UUV), it is assumed that UUV optimization will lead the unmanned priority list. Acting as a mothership, SSN(X) will be able to deploy these UUVs to perform a variety of tasks, including gaining a greater awareness of the battlespace, targeting, active deception and other classified missions. To fulfill its destiny, UUV employment must be a consideration in every frame of SSN(X) and subjected to rigorous analysis.

SSN(X) must be capable of the deployment, recovery, and command and control of UUVs. To fulfill this mission, every aspect of contemporary submarine-launched UUV operations will need to scale dramatically. Submarine designers and undersea warriors need to understand the trade space available in order to gain an enhanced understanding of potential SSN(X) UUV employment. A detailed study of the trade space must include all relevant aspects of the deployment lifecycle including UUV acquisition, operation, sustainment and maintenance. The following analysis provides a first approximation of the undersea trade space where the Apex Predator’s ultimate form will take shape.

UUV Concept of Operations

Effective solution design of SSN(X) and UUVs can only come from a mature concept of operations (CONOPS). These CONOPS will center around the use cases for submarine launched UUVs. UUVs will provide SSN(X) the ability to monitor greater portions of the battlespace by going out beyond the range of the SSN(X)’s organic sensors to search or monitor for adversary assets. The ability to search the environment, both passively and actively, will be key to fulfilling the CONOPS. Additionally, active sonar scanning of the seabed, a current UUV mission, will continue to be a key UUV mission. These are by no means the only missions that UUVs could or will perform, rather they examples of relevant missions that enhance the combat power of SSN(X).

It is critical that CONOPS developers and acquisition planners consider the SSN(X) and its UUV as an integrated system. That integrated system includes the SSN(X) mothership as well as the UUV bodies, crew members required to support UUV operations and the materiel support strategy for deployed UUVs. Other categories are necessary for consideration, but each of these provides a measurable constraint on SSN(X) CONOPS development. While the acquisition of UUV and SSN(X) may ultimately fall under separate Program Executive Offices, the Navy must heed the lessons of Littoral Combat Ship’s (LCS) inconsistent funding of mission modules.2 One of LCS’s early woes related to the failure to develop mission modules concurrently with LCS construction. Absent the mission modules, early LCS units bore criticism for lacking combat capability. Instead, the Navy should draw on the success of iterative capability developments like the Virginia Payload Module (VPM).3 In the same way Virginia-class introduced incremental capability improvements across its Block III through Block V via VPM, the Navy must prioritize continuous UUV development just as urgently as it pursues its next submarine building initiative. Table 1 lists some priority considerations:

Category Elements for Consideration
UUV Size of the UUVs carried inboard
Quantity of embarked UUVs
Deployment methods of UUV
Communications between SSN(X) and UUV
UUV Crew UUV Support Crew Size
Training requirements for UUV Sailors
Materiel Support Strategy Charging and recharging UUVs inboard
Maintenance strategy for UUV
UUV load and unload facilities

Table 1. UUV Considerations

Designing SSN(X) for UUVs

Organic UUV operations are the desired end state, but several gaps exist between the Navy’s current UUV operational model and the Navy’s stated plans for SSN(X). At present, submarines deploy UUVs for specific exercises, test and evaluations, or carefully planned operations.4 Additionally, UUV missions require specially trained personnel or contractors to join the submarine’s crew to operate and employ the UUV system, limiting operational flexibility. To their credit, today’s SSNs can deploy UUV from a number of ocean interfaces according to the size of the UUV including: 3” launcher, the trash disposal unit, torpedo tubes, lock-in/lock-out chamber, missile tubes, large ocean interfaces or dry-deck shelters.5 However, the ability to perform UUV-enabled missions depends heavily on the legacy submarine’s mission configuration. Two decades ago, the Virginia-class was designed to dominate in the littorals and deploy Special Forces with a built-in lock-in, lock-out chamber. Just as every Virginia-class submarine is capable of deploying Special Forces and divers, every SSN(X) must be UUV ready.

In order to fully define the requirements of the Apex Predator, requirements officers and engineers within the undersea enterprise must understand the trade space associated with UUV operations. SSN(X) must exceed the UUV capabilities of today’s SSNs and should use resources organic to the ship, such as torpedo tubes, to employ them. Also, given that Navy requirements need SSN(X) to transit at maximum speed, these UUVs will need to present low appendage drag or stay within the skin of the submarine until deployed.6 Similar to the internal bomb bay configuration of Fifth Generation F-35 Stealth Fighters, internally-housed UUVs, most likely with the form-factor of a torpedo, will likely yield the greatest capacity while preserving acoustic superiority at high transit speeds.

With so many variables in play and potential configurations, requirements officers need the benefit of iterative modeling and simulation to illuminate the possible. Optimization for UUV design is not merely a problem of multiplication or geometric fit. Rather, an informed UUV model reveals a series of constraining equations that govern the potential for each capability configuration. The following analysis examined over 300 potential UUV force packages by varying the number UUVs carried, the size of the UUV crew complement, and UUV re-charging characteristics in-hull, while holding the form-factor of the UUV constant. Appendix 1 provides a detailed description of the first order analysis, focused on mission-effectiveness, seeking to maximize the distance that a UUV compliment could cover in a 24-hour period. Notably, the UUV sustainment resources inside the submarine matter just as much as the number of UUVs onboard. Such resources include maintenance areas, charging bays, weight handling equipment and spare parts inventory.

Given that SSN(X) and its unmanned systems will likely be fielded in a resource constrained environment, including both obvious fiscal constraints and physical resource constraints within the hull, a second order analysis scored each force package on maximum utilization. After all, rarely-utilized niche systems are often hard to justify. While more UUVs generally resulted in a potential for more miles of UUV operations per 24-hour period, smaller numbers of UUVs in less resource-intensive configurations (that is, requiring less space, less operational support, etc.) achieved up to 5x higher utilization scores. Given the multi-mission nature of SSN(X) and the foreseeable need to show high utilization in the future budgetary environment, requirements officers have a wide margin of trade space to navigate because many different types and configurations of UUVs could achieve high utilization rates as they performed various missions.

What should be Considered

SSN(X) will be enabled by advanced technologies, but its battle efficiency will rely just as much on qualified personnel and maintenance as on any number of advanced sensors or high endurance power systems. In order to identify the limiting factor in each capability configuration, the study varied the following parameters according to defined constraint equations to determine the maximum number of miles that could be scanned per 24-hours: number of UUVs, size of the UUV support crew, the UUV support crew operational tempo, the number of UUV charging bays, and the numbers or charges per day required per UUV. As a secondary measure, the UUV utilization rate for each capability configuration was determined as a means of assessing investment value. The constraint equations are provided in full detail in Appendix 1: Analysis Constraint Equations.

The Navy currently fields a variety of UUVs that vary in both size and mission. The opening vignette of this essay discusses UUVs that can be launched and recovered from submarine torpedo tubes while submerged, which the Navy’s lexicon classifies as medium UUVs (MUUV) and which this study uses as the basic unit of analysis. The current inventory of MUUVs include the Razorback and Mk-18 systems, but this analysis used the open-source specifications of the REMUS 600 UUV (the parent design of these platforms) to allow releasability. These specifications are listed in Table 2, and Table 3 assigns additional values to relevant parameters related to UUV maintainability based on informed estimates. While the first SSN(X) will not reach initial operating capability for more than a decade, the study assumed UUV propulsion system endurance would only experience incremental improvements from today’s fielded systems.7

Remus 600 Characteristics
Mission Speed 5 knots
Mission Endurance between Recharges 72 hours
Number of Sensors (active or passive) 3

Table 2. Remus 600 Characteristics

Informed Estimates on Maintainability
Maintenance Duty Cycle 0.02
Sensor Refit Duty Cycle 0.09
Duty Cycle Turnaround 0.23

Table 3. Informed Estimates on Maintainability

Model Results and Analysis

The Navy’s forecasted requirements for SSN(X) weapons payload capacity mirrors the largest torpedo rooms in the Fleet today found on Seawolf-class submarines. Seawolf boasts eight torpedo tubes and carries up to 50 weapons.8 Assuming SSN(X)’s torpedo room holds an equivalent number of weapons stows, some of these stows may be needed for UUVs and UUV support.

Trial values from the trade study for specific UUV, crew, and operational tempo (OPTEMPO) capability configurations are shown in Table 4:

Parameter Values
Number of UUVs 2, 3, 4, 5, 6, 7, 8
Number of UUV Crew Watch Teams 2, 3, 4
Crew OPTEMPO 0.33, 0.5
Number of UUV Charging Bays 2, 4, 6, 8
Daily Charges per UUV 0.33, 0.5

Table 4. Study Parameters

The number of crew watch teams could represent a multiple based on the ultimate number of personnel required to sustain UUV operations. Crew OPTEMPO represents the time that UUV operations and maintenance personnel are on duty during a 24-hour period. A value of 0.33 represents three 8-hour duty sections per day. 0.5 represents two 12-hour duty sections per day.

The results in Table 5 represent seven of the highest scoring capability configurations from among the 336 trials in the trade study.9 The most significant variable driving UUV miles scanned was the number of UUV Crew Watch Teams, and the second most significant variable was the UUV Crew OPTEMPO. UUV configurations with 3, 4, 5, 6, 7, or 8 UUVs all achieved the maximum score on scan rate of 240 miles scanned per 24 hours, though utilization rates were much higher for the configurations with fewer UUVs. The 3 UUV configuration was able to achieve 240 miles with the fewest number of UUVs and yielded the second highest utilization score. The 2 UUV configuration earned a slightly higher utilization score (+2%), but the scan rate was 42% less than the 3 UUV configuration. 

# UUV # Crew Crew OPTEMPO UUV Charging Bays Charges per Day Miles Scanned per 24 hrs Utilization Notes
8 4 0.5 2 0.33 240 0.25 Big footprint; High scan rate; Low utilization
7 4 0.5 2 0.33 240 0.29 Big footprint; High scan rate; Low utilization
6 4 0.5 2 0.33 240 0.33 Medium footprint; High scan rate; Low utilization
5 4 0.5 2 0.33 240 0.4 Medium footprint; High scan rate; Medium utilization
4 4 0.5 2 0.33 240 0.5 Medium footprint; High scan rate; High utilization
3 4 0.5 2 0.33 240 0.67 Small footprint; High scan rate; High utilization
2 3 0.5 2 0.33 165 0.69 Smallest footprint, Medium scan rate; Highest utilization

Table 5. Sample Analysis Results 

This study shows that in order to scan more miles, loading more UUVs is not likely to be the first or best option. Understanding of this calculus is critically important since each additional UUV would replace a weapon needed for combat or increase the overall length, displacement and cost of the submarine. Instead, crew configurations and watch rotations play a major factor in UUV operations.

Conclusion

The implications for an organic UUV capability on SSN(X) go far beyond simply loading a UUV instead of an extra torpedo. The designers of SSN(X) will have to consider personnel required to operate and maintain these systems. The spaces and equipment necessary to repair, recharge, and maintain UUVs will have to be designed from the keel up.

The Apex Predator must be more than just the number and capability of weapons carried. SSN(X)’s lethality will come from the ability of sailors to man and operate its systems and maintain the equipment needed to perform in combat. The provided trade study sheds light on the significant technical challenges that still remain in the areas of UUV communications, power supply and endurance, and sensor suites. By resourcing requirements officers, technical experts and acquisition professionals with a meaningful optimization study, early identifications of UUV requirements for SSN(X) can enable the funding allocations necessary to solve these difficult problems.

Lieutenant Commander James Landreth, P.E., is a submarine officer in the Navy Reserves and a civilian acquisition professional for the Department of the Navy. He is a graduate of the U.S. Naval Academy (B.S.) and the University of South Carolina (M.Eng.). The views and opinions expressed here are his own.

Lieutenant Andrew Pfau, USN, is a submariner serving as an instructor at the U.S. Naval Academy. He is a graduate of the Naval Postgraduate School and the U. S. Naval Academy. The views and opinions expressed here are his own.

Appendix 1: Analysis Constraint Equations

The following equations were used to develop a reusable parametric model. The model was developed in Cameo Systems Modeler version 19.0 Service Pack 3 with ParaMagic 18.0 using the Systems Modeling Language (SysML). The model was coupled with Matlab 2021a via the Symbolic Math Toolkit plug-in. This model is available to share with interested U.S. Government parties via any XMI compatible modeling environment.

Number of Miles Scanned per 24 hours=Number of Available Systems*Speed*24

Equation 1. Scanning Equation

Number of Available Systems= min⁡(Number of Available UUV,UUV Crew,Number of Available Charges)

Equation 2. System Availability Equation

Number of Available UUV=((Number of Available UUVs by Day+Number of Available UUVs by Night)*UUV Duty Cycle)/2

Equation 3. UUV Availability Equation

Number of Available UUV=((Number of Available UUVs by Day+Number of Available UUVs by Night)*UUV Duty Cycle)/2

Equation 4. UUV Duty Cycle Equation

Number of Available UUVs by Day=min⁡(number of day sensors,number of UUVs)

Equation 5. Day Sensor Availability Equation

Number of Available UUVs by Night=min⁡(number of night sensors,number of UUVs)

Equation 6. Night Sensor Availability Equation

Number of Available Crews=Number of Crews*Crew Time On Duty

Equation 7. Crew Availability Equation

Number of Available Charges=(Charges per Day)/(Daily Charges per UUV)

Equation 8. Charge Availability Equation

Utilization= (Number of Miles Scanned per 24 hours)/((Number of UUVs*Patrol Speed*24 hours))

Equation 9. Utilization Score 

Endnotes

1. Justin Katz, “SSN(X) Will Be ‘Ultimate Apex Predator,’” BreakingDefense, July 21, 2021, https://breakingdefense.com/2021/07/ssnx-will-be-ultimate-apex-predator/

2. Congressional Research Service, “Navy Littoral Combat Ship (LCS) Program: Background and Issues for Congress,” Updated December 17, 2019, https://sgp.fas.org/crs/weapons/RL33741.pdf

3. Virginia Payload Module, July 2021, https://sgp.fas.org/crs/weapons/RL32418.pdf

4. Megan Eckstein, “PEO Subs: Navy’s Future Attack Sub Will Need Stealthy Advanced Propulsion, Controls for Multiple UUVs,” USNI News, March 9, 2016, https://news.usni.org/2016/03/09/peo-subs-navys-future-attack-sub-will-need-stealthy-electric-drive-controls-for-multiple-uuvs

5. Chief of Naval Operations Undersea Warfare Directorate, “Report to Congress: Autonomous Undersea Vehicle Requirement for 2025,” p. 5-6, February 2016, https://www.hsdl.org/?abstract&did=791491

6. Congressional Research Service, “Navy Next-Generation Attack Submarine (SSN[X]) Program: Background and Issues for Congress,” May 10, 2021, https://s3.documentcloud.org/documents/20705392/navy-next-generation-attack-submarine-ssnx-may-10-2021.pdf

7. Robert Button, John Kamp, Thomas Curtin, James Dryden, “A Survey of Missions for Unmanned Undersea Vehicles,” RAND National Defense Research Institute, , 2009, p. 50, https://www.rand.org/content/dam/rand/pubs/monographs/2009/RAND_MG808.pdf

8. U.S. Navy Fact Files, “Attack Submarines – SSN,” Updated May 25, 2021, https://www.navy.mil/Resources/Fact-Files/Display-FactFiles/Article/2169558/attack-submarines-ssn/

9. The results of all 336 capability configurations are available in .xlsx format upon request.

Featured Image: PACIFIC OCEAN – USS Santa Fe (SSN 763) joins Collins Class Submarines, HMAS Collins, HMAS Farncomb, HMAS Dechaineux and HMAS Sheean in formation while transiting through Cockburn Sound, Western Australia.