Category Archives: Capability Analysis

Analyzing Specific Naval and Maritime Platforms

Searching for Lost Submarines: An Overview of Forensic Underwater Methodologies

By Andrew Song

How does one find an object not meant to be found? Forensic maritime investigators in 2017 stumbled across this question when searching for the disappeared ARA San Juan (S-42) – an Argentinian submarine whose mission centered around stealth. Despite the environmental challenges and the restrictions imposed by the profile of submarines, several complementary forensic tools have emerged as authoritative standards and best practices for underwater search operations. These include: (1) optimization of preliminary search boxes through Bayesian probabilities, with updates for posterior probabilities throughout the search; (2) side-scanning sonar systems; and (3) unmanned underwater vehicles (UUVs) for imagery, access, and identity verification. In explaining the efficacies and drawbacks of such methods, this analysis highlights the importance and evolving future of search optimization strategies.

How to Find a Lost Submarine

Forensic maritime investigators confront distinct challenges not relevant for traditional land-based investigations. Unlike terrestrial-based forensics, pre-established knowledge of a local maritime environment is sparse. Scientists have mapped 1/5th of the sea floor to modern standards with 100m resolution, but that means almost 290 million square kilometers of seafloor—twice the surface area of Mars—have not yet been surveyed.1 Furthermore, the remoteness of submarine operational areas casts a wide speculative net for a submarine’s last location, acting as a red herring for planners. For instance, the French Navy finally found the Minerve in July 2019 after searching since 1968, but the submarine’s position was only 28 miles off the coast of Toulouse.2

Debris from the French submarine Minerve. The letters MINE from the Minerve’s name are visible in the wreck. The Minerve was lost in January 1968. (French Navy photo)

The absence of existing charts, therefore, necessitates simultaneous 4-D mapping of the area—which is in short supply. Submarine debris is unidentifiable in satellite and aerial images due to surface opacity and the extreme depth of wreckages. Stratification conceals wreckage and clearing sedimentary buildup becomes extremely complicated due to sheer volume. An onsite “walk-over” survey, as described by Fenning and Donnelly3 in their description of geophysical methodologies, is simply impossible in a marine environment. Acidity and pH levels of the water also influence rates of decomposition, and must be considered for a simulation in the casualty scenario.

August 1986 – A view of the detached sail of the nuclear-powered attack submarine USS Scorpion (SSN-589) laying on the ocean floor. Depth 10,000 feet, 400 miles southwest of the Azores. The Scorpion was lost on May 22, 1968. (Photo via U.S. National Archives)

1: Bayesian Search Strategies

Constructing a preliminary search box requires meticulous strategizing and calculations. An error associated with misanalysis of primary sources can inevitably mislead search and rescue planners, delaying a submarine’s discovery. This occurred in the case of the USS Grayback, as Navy officials mistranslated the final coordinates of the submarine documented by a Japanese carrier-based bomber.4 An incorrectly interpreted digit in the longitudinal coordinates created an erroneous search area straying 160 kilometers from the Grayback’s actual location.5

Pitfalls in relying on a single source cause planners to use search strategies based on Bayesian statistics. At a rudimentary level, Bayes’ theorem leverages probabilities of an event and prior knowledge regarding the condition of such event to produce a reasonable prediction of an event’s occurrence. Stakeholders will first formulate a range of possible stories surrounding a missing submarine’s location, pulling from all potential sources (eyewitness testimony of submarine’s last submergence, operational logs, mission record, etc.). The credibility and value of each piece of evidence will be judged by investigators and experts who will then collectively assign statistical weight to possible scenarios. For instance, the USS Scorpion’s forensic team invited experienced submarine commanders to present reasonable hypotheses that the scientists would later input into a probability density function.6 Such probability density functions assist planners in prioritizing certain search zones for surveying. Investigators resort to Bayesian statistics and Bayesian inference models because of its predictive power and the comprehensive results derived from relatively few inputs. Figure A demonstrates a four-step hierarchical convention in a Bayesian search strategy. The diagram summarizes the effects of updates on the model and introduces the posterior probability function (PPF).

Figure A.

When a search area fails to yield any evidence pointing to a submarine, a posterior probability function will be calculated. A PPF’s utility and role is best explained by Equation (1-2)’s hypothetical representation of a grid square’s probability of containing a submarine. Variable q represents the probability of successful detection of a wreck and p quantifies the probability that the grid square does contain the wreck. Failing to find a wreck in a grid square will revise the probability of that grid square into p prime—a posterior probability.7 In this theoretical situation, the probabilities (for purely illustrative purposes) are: that a wreck in the grid square is 67% and the chances of a side-scan sonar identifying an anomaly is 85%.

Under those numeric assumptions, if the submarine were not found in the first survey, then a second survey of the same grid square, as denoted in Equation (3), will yield a secondary posterior probability of approximately 4.2%. Taken together, 4.2% represents the chances of success in finding the submarine in the given grid square in a second sweep.

Bayesian strategies are a staple of operations analysis search theory. For instance, the U.S Coast Guard incorporates Bayesian search strategies into its Search and Rescue Optimal Planning System (SAROPS).8 Successful outcomes produced by Bayesian search strategies have led to a general consensus on the technique’s utility. Identification of the underwater wreckage site of Air France Flight AF 477 underscored this utility. In the 2011 discovery, investigators created probability density functions (PDFs) from weighted scenarios supplemented by anterior knowledge of nine commercial aircraft accidents, known flight dynamics, and final trajectories.9 These PDFs drew search boxes that broadened until a Brazilian corvette recovered components of AF 477 buoyed on the surface.

Stern view of the nuclear-powered attack submarine USS Scorpion (SSN-589) showing the upper portion of the rudder (with draft markings) and the port stern plane. Note that the after portion of the engine room section (has been) telescoped into the machinery room. The ribs of the stern planes can be seen due to the deformation of the metal covering them. (Official U.S. Navy Photograph, from the collections of the Naval History and Heritage Command.)

However, Bayesian search strategies warrant legitimate criticism for their implicit use of subjective analysis. Terrill and Project Discover’s usage of Bayesian search strategies narrates a story of arbitrary values associated with each scenario. This is seen especially when the researchers place heavy subjective weight on interview data from the few remaining witnesses of a B-24 bomber’s last location.10 Taken together, Bayesian search strategies force analysts to quantify what is essentially qualitative information (e.g., the probability that an elderly man can accurately recall the events of the crash). These limitations create possibilities for higher uncertainty and a wider confidence interval. In addition, Bayesian search strategy can overshadow other powerful methods to form search boxes such as a Gittins index formula.11

2: Implementation of Side-Scanning Sonar for Seabed Imaging

Sonar, otherwise known as sound navigation and ranging, is a method that leverages sound propagation as a way to detect an object’s position and to visualize shapes from acoustic signatures in the form of echoes. The return frequency and radiated noise of an object allow for target acquisition and safe navigation by submarines dependent on the vicinity’s sound velocity profile; for researchers hoping to find inactive submarines, side-scan sonars lend mapping capabilities.

These devices construct images from cross-track slices supplied by continuous conical acoustic beams that reflect from the seafloor—wave emission speed can reach nearly 512 discrete sonar beams at a rate of 40 times a second.12 Data produced by side-scan sonars assembles a sonogram that converts into a digital form for visualization. The utility of side scan sonars is trinitarian; they create effective working images of swaths of sea floor when used in conjunction with bathymetric soundings and sub-bottom profiler data.13 Form factors of side-scan sonars allow the device to be highly mobile and serve as flexible, towable attachments for the tail of any-sized ships, giving liberty to human operators to adjust the directionality of ensonification. In addition, side-scan sonars contain adjustable frequency settings. A change in a side-scan sonar’s frequency will affect the sonar’s emitting wavelength, giving the operator flexibility on target acquisition. Side-scan sonars can operate as low as the 50kHz range to cover maximum seabed area; alternatively, the instrument can operate at 1 MHz for maximum resolution. This feature is extremely vital because submarines alter in length by model and different bodies of water share unique sound velocity profiles. Another advantage with side-scan sonars is their high precision record at sub-meter accuracy level for horizontal planes and at the centimeter-error level for vertical planes.14

Side-scan sonar systems exist as a vital apparatus to any search operation because the alternatives for mapping are minimal. Methods other than side-scan sonars like low-frequency multi-beam bathymetric data scanners, when reappropriated, are imperfect in object identification accuracy and better for scanning large seabed topographic structures like underwater mountains.15 Recent advances in magnetic anomaly detectors16 appear promising for future seabed exploration, but these instruments still require parallel approaches or in-tandem usage with side-scan sonars. Until magnetometers can extend their range beyond identifying magnetic objects in the Epipelagic Zone—the uppermost layer of the ocean where sunlight is still available for photosynthesis—side-scan sonars will be more consistent and versatile than magnetometers.

A mosaic of combined sonar images shows how close the Titan submersible was to the Titanic debris field. The Titan was lost on June 18, 2023. (Graphic via RMS Titanic Inc.)

Deployment of side-scan sonar occurs in the intermediary stage of search operations. A vessel will have a side-scan sonar mounted on or embedded in a towfish. Tethered to the main vessel, the side-scan sonar will perform a proper sonar survey of a proposed area by maintaining a rigid survey line along with a consistent towfish “altitude” when trailing the ship. Technicians carefully check the GPS receiver of the towfish to rectify course deviations, if needed, by manually changing the ship and towfish’s heading. A side-scan sonar operates with a survey mode to capture anomalies, which visual graphs will register and mark for later investigation by an unmanned underwater vehicle (UUV).

Unfortunately, handlers of side-scan sonars will notice several limitations that must be accommodated. A restriction to side-scan sonars is their inability to image directly below side-scan transducers. In other words, ships must compensate for a side-scanner’s blind spot by staggering their mow-the-lawn strategy. In addition, side-scan sonars contain software that prohibits the surpassing of a certain speed limit for towing, lest the receiver show significant scattering, absorption, and incoherent imagery. Like other instruments, side-scan sonars’ physical power consumption can be a variable for constraint.

Lastly, side-scan sonars perform according to the quality of the bathymetric data supplied. By themselves, side-scan sonars cannot efficiently identify changes in gradients and sound velocity profiles in real-time. High frequency/high resolution sonars operate at relatively short ranges via direct path sound propagation, which limits the refraction of sound waves and consequent distortion. This means the side-scan sonar will have a handicap in reporting the propagation paths of its rays and the sound channels, meaning knowledge of shadow zones may be omitted.17 This is a search investigator’s worst nightmare because failure to adequately search a grid may lead to incorrect, permanent marking of a square not holding a target. Imperfect data or simply lack of bathymetry data also contribute to the limitation of side-scan sonars.

3: Integration of Adaptive Unmanned Underwater Vehicles for Forensic Searches.

Since their introduction in the 1960s, UUVs have played a major role in every forensic investigation for a lost submarine. UUVs act as surrogates to human divers who cannot comfortably operate for extended periods of time at depths greater than 100 meters. To illustrate the need for UUVs, the USS Grayback was discovered at a depth of 1,417 feet (431 meters)18 — an impossible depth for divers, but not for the submarine itself. UUVs support forensic scientists in more than just underwater photography. UUVs collect bathymetry data, use ultrasonic imaging, measure strength of ocean currents, and detect foreign objects by their inertial or magnetic properties. Variants of UUVs are categorized into two robotic classes: remotely operated underwater vehicles (ROVs) and autonomous underwater vehicles (AUVs). ROVs allow for direct piloting by a human operator from a remote location with signal. AUVs function independently and follow pre-programmed behavioral search patterns.

A photo taken by a remotely operated vehicle (ROV) shows the sunken Indonesian Navy submarine KRI Nanggala-402 in Denpasar, Bali, Indonesia, May 18, 2021. KRI Nanggala-402 was lost on April 20, 2021. (Indonesian Navy photo)

The UUV variant, Remus 100,19 manufactured by Woods Hole Oceanographic Institute, deceptively resembles a torpedo, but functions as an effective explosive ordnance disposal detection device for the Navy. When refitted for search operations, the Remus (AUV) variant can perform dual-frequency side-scan sonar operations in independent mow-the-lawn search sequences.20 The Remus’ transponder wields GPS and doppler velocity logs that have proven to be more accurate in measurements than earlier AUVs. Customarily, forensic actors will deploy ROVs and AUVs for close-up identification or routine investigation of an anomaly, instead of wide-area search missions. These ROVs display high-definition, colorized video feeds for operators on a vessel; the latency between pilots and the ROV ranges from one to two seconds, making for fast time on responsive decisions.


This analysis examines a trinity of contemporary methods revolving around statistics and autonomous vehicles that aid officials in search and rescue operations for submarines. Corporations and officials should note that innovating and constructing more effective models in search operation becomes worthwhile when speed determines the ability to save lives. While this analysis discusses the employment of the aforementioned technology in the context of submarines, these methods can be theoretically implemented for other maritime interests: finding missing planes, undertaking the historical preservation of shipwreck sites, and embarking on deep-sea mining. For all these reasons, the U.S. has an inherent stake in advancing a discussion about progress in submarine search and rescue tactics.

Andrew Song is a U.S. Navy Nuclear Submarine Officer. His previous publications have appeared in The Wall Street Journal, The National Interest, Military Review, Journal of Indo-Pacific Affairs, and ProceedingsHe graduated with a B.A. in Global Affairs from Yale University in 2022.


1 Amos, Jonathan. “One-Fifth of Earth’s Ocean Floor Is Now Mapped.” BBC News. BBC, June 20, 2020.

2 “DOS Involved in the Finding of the French Submarine La Minerve.” Deep Ocean Search, October 3, 2019.

3 Fenning, P. J., Donnelly, L. J., 2004. Geophysical techniques for forensic investigation. Geological Society of London Special Publications, 232, 11-20.

4 Elfrink, Tim. “A WWII Submarine Went Missing for 75 Years. High-Tech Undersea Drones Solved the Mystery.” The Washington Post. WP Company, November 11, 2019.

5 Ibid.

6 L.D. Stone, “Operations Analysis during the Underwater Search for Scorpion” Naval Research Logistics Quarterly, vol. 18(2), pp. 141–157. 1971

7 Terrill, E., Moline, M., Scannon, P., Gallimore, E., Shramek, T., Nager, A., Anderson, M. (2017). Project Recover: Extending the Applications of Unmanned Platforms and Autonomy to Support Underwater MIA Searches. Oceanography, 30(2), 150-159. Retrieved March 1, 2021, from

8 Stone, L. (2011). Operations Research Helps Locate the Underwater Wreckage of Air France Flight AF 447. Phalanx, 44(4), 21-27. Retrieved March 2, 2021,

9 Soza & Company, Ltd. (1996). The Theory of Search: A Simplified Explanation: U.S. Coast Guard. Contract Number: DTCG23-95-D-HMS026. Retrieved on 2010-07-18 from

10 Terrill, E. “Project Recover.” Oceanography 2017.

11 Weitzman, Martin L. (1979). “Optimal Search for the Best Alternative”. Econometrica. 47 (3): 641–654.

12 “Side Scan Sonar.” Exploration Tools: Side Scan Sonar: NOAA Office of Ocean Exploration and Research, 2002.

13 Jean M. Audibert, Jun Huang. Chapter 16 Geophysical and Geotechnical Design, Handbook of Offshore Engineering, Elsevier, 2005. ISBN 9780080443812,

14 Aaron Micallef. Chapter 13: Marine Geomorphology: Geomorphological Mapping and the Study of Submarine Landslides, Development in Earth Surface Processes, Elsevier, Vol 15, 2011, pg 377-395 ISBN 9780444534460, (

15 Elfrink, “A WWII Submarine went Missing” The Washington Post. 2019.

16 Geophysical Surveying Using Magnetics Methods, January 16, 2004, University of Calgary

17 “Side Scan Sonar.” United States Naval Academy , February 1, 2018. (2) Sonar Propagation. Department of Defense . Accessed April 7, 2021.

18 Elfrink, “A WWII Submarine went Missing” The Washington Post. 2019.

19 REMUS”. Woods Hole Oceanographic Institution.

20 J. Ousingsawat and M. G. Earl, “Modified Lawn-Mower Search Pattern for Areas Comprised of Weighted Regions,” 2007 American Control Conference, New York, NY, USA, 2007, pp. 918-923, doi: 10.1109/ACC.2007.4282850.

Featured Image: August 1986 – A view of the detached sail of the nuclear-powered attack submarine USS Scorpion (SSN-589) laying on the ocean floor. The starboard fairwater plane is visible protruding from the sail. Masts are visible extending from the top of the sail (located at the lower portion of the photograph). A large segment of the after section of the sail, including the deck access hatch, is missing. (Official U.S. Navy photograph)

The Royal Canadian Navy Must Be Equipped for Real-World Pacific Scenarios

By Dr. Julian Spencer-Churchill and Alexandru Filip


With tension level ever increasing in the Pacific, Canada must prepare for future naval threats from revisionist states, which threaten international order and the peace of fellow democracies. In August, Ottawa deployed three frigates of the Royal Canadian Navy (RCN) to the Pacific to demonstrate freedom of navigation against encroachments by the Chinese Coast Guard. This posturing, coupled with a willingness to act along side allies, sends a strong signal of determination to maintain international norms, while also preparing for a fight against aggravating Chinese and Russian hostilities which will no doubt pull Canada into a wider conflict if deterrence fails. But Canada’s current naval capabilities fall short of meeting great power threats, which may diminish its usefulness in supporting allies in a Pacific conflict.

Canadian Mission Sets in Pacific Conflict

In the event of war in the Pacific, most likely confronting China over Taiwan, Ottawa will adopt postures and mission sets in support of allies. Canadian military missions could consist of a wide range of missions to include convoy protection across the Pacific (possibly up to the East coast ports of Taiwan, Philippines and Okinawa) with an emphasis on anti-submarine warfare (ASW), air defense against long-range and submarine-launched and island-based missiles, and littoral duties to include defense against small attack craft hidden in estuaries.

Beyond warfare mission sets, Canadian military forces could be used for blockade enforcement in the open seas, along the Ryukyu Islands, at the Malacca, Sunda, Lombok and Makassar straits of Indonesia, the Straits of Hormuz, and in the Indian Ocean against Chinese allies like Iran, Pakistan, Sri Lanka, Bangladesh, and Myanmar. If the Kremlin provides material support to Beijing, the Royal Canadian Navy (RCN) could assist or reinforce U.S. arctic inspections for war contraband at the Bering Strait and the Northwest Passage. Canadian military forces could also help escort U.S., Japanese, or British aircraft/helicopter carrier groups operating in the Philippine Sea or the Indian Ocean. Canadian military forces could also provide support to other allied platforms capable of conducting long-range deep strike missions against bases and sensors within mainland China. However, supporting such a kinetic mission sets during wartime may escalate Chinese Communist Party (CCP) retaliation to Canadian soil attacks from conventional hypersonic weapons against economic targets such as at Fort McMurray in Alberta, or the Great Whale hydroelectric projects in Quebec.

PACIFIC OCEAN (July 18, 2016) The Royal Canadian Navy Halifax-class frigate Her Majesty’s Canadian Ship Calgary (FF 335) transits the Pacific Ocean during Rim of the Pacific 2016. (U.S. Navy photo by Mass Communication Specialist 2nd Class Ryan J. Batchelder)

Canadian military forces could also conduct surveillance of key transhipment points against states Beijing-aligned states, such as the Republic of South Africa and the Cape of Good Hope, and Cuba and the Panama Canal. In the unlikely contingency of an attempted breakout from the first island chain of the Chinese PLAN (People’s Liberation Army – Navy), Canada’s Harpoon-equipped Halifax class frigates may be employed as part of a surface action group (SAG). Canadian ASW helicopters operating from the deck of the Halifax frigates, and Aurora maritime surveillance aircraft, could also could also support high-risk contingency mission such as assisting allied submarines to hunt the PLAN’s six Jin class ballistic missile submarines (SSBNs) in the South China Sea, the Central Pacific, or even Russia’s SSBN bastion in the Sea of Okhotsk.

The Canadian military could also provide at-sea-replenishment, a key enabling mission to overcome vast distances involved in a Pacific campaign. This mission could be will be fulfilled by Protecteur class vessels, currently being built. All of these contingencies will involve the RCN, in conjunction with Canada’s maritime surveillance capabilities, to operate from allied Pacific bases, such as in Japan, the Philippines, or Taiwan, protected by elements of the Royal Canadian Air Force (RCAF) and Army.

Canada’s Naval Capabilities

Canada’s current naval capabilities are inadequate for a determined operation in the Pacific theater. Canada currently has 12 multi-role Halifax class frigates, four Victoria class submarines, and 14 CP-140 Aurora maritime patrol aircraft. These platforms, and Ottawa’s future Canadian Surface Combatant (CSC), must be assessed as seriously deficient compared to their most likely combat missions. Modern vessels are judged by the numbers of vertical launch system (VLS) tubes, of which the U.S. has 9,044, China has at least 2,000, and Canada will have zero built-in VLS for at least the next half-decade. Canada’s 288 obsolete above-deck VLS on its Halifax frigates, are far more vulnerable to shrapnel.

The current Halifax class frigates that are the mainstay of the Canadian surface fleet are outclassed and limited in combat against opposing navy’s ships or even as deterrents. Their older Sea Giraffe 180 HC and SMART-S MK2 radars only provide surface and air radar coverage to a maximum of 100 and 135 nautical miles, respectively.

For comparison, PLAN’s most common frigate, the Type 054A Jiangkai II (of which they have around 30 vessels) has a Type 366 radar. This variant is a reworked Chinese version of the Russian MR-331 Mineral-ME radar, covers surface targets to 135 nautical miles. It also possesses a Type 382 radar, an adaptation of the Soviet MR-710 Fregat M2EM present on Russian Sovremennyy class destroyers, which provides coverage to 161 nautical miles for air and surface searches. In terms of weaponry, the PLAN Type 054 outperforms the Halifax class in the form of its YJ-83 anti-surface ship missile (100 nautical mile range) outfitted with 32 VLS cells, which exceeds the Halifax’s compliment of RGM-84L Harpoon II (75 nautical mile range). While it may seem that the disadvantages posed to Jiangkai II are peripheral, these seemingly marginal issues will be further compounded because the RCN will be operating in an environment in which it is outnumbered. It will also be deployed against a seemingly pervasive littoral air threat in the form of PLAAF (People’s Liberation Army – Air Force) H-6 bombers and other sea denial anti-ship cruise and ballistic missiles.

Despite the present surface capability gap, the Canadian Surface Combatant (CSC) project of fifteen warships by the early-2030s, offers enhanced capabilities for many of the Royal Canadian Navy’s future operational requirements. Each CSC will feature multi-load-out capable 32 VLS, AN/SPY-7 radar, and RIM-66M-6 (maximum range of 90 nautical miles) missiles that will enable a far greater surface to air capability. The BridgeMaster E radar provides a surface search capability of around 96 nautical miles, which is a slight reduction from the Halifax class, but compensates with a complement of RGM-184A Naval Strike Missiles (NSMs) with a 100 mile range.

This puts the CSC a step above the Halifax-class with radar and weapon arrangements that are closer to China’s Type 052 Luyang III, China’s most common destroyer class. While the Luyang class fields YJ-18 Anti-Ship Cruise Missile (ASCM), which boasts a range of around 300 nautical miles, the CSC fields Block IV Tomahawk cruise missiles (Raytheon has been looking at turning into antiship missiles for naval combat). Their retrofit could offer a solution to longer range targeting and act as a deterrent against Chinese and even Russian surface vessels, allowing these ships to engage in blockade operations along strategic sea lines of communication from a significant distance. This would allow the RCN to carry out escort missions supporting convoys through the Indonesian Archipelago to Australia, Japan, and Taiwan, while also providing surface, air, and anti-access/area-denial (A2/AD) against Chinese long-range bombers and attack aircraft.

Concept image of the Canadian Surface Combatant. (Canadian government photo)

The PLAAF H-6s principal anti-ship missiles (ASM) ordnance outranges the CSC’s anti-air capability. However, the H-6’s Type 245 radar only has a range of 150km, and the CSC’s Electronic Warfare (EW) countermeasures could jam the bomber’s sensors, and even the Airborne Early Warning (AEW) radar of Chinese aircraft patrolling nearby, from exactly pinpointing its location, forcing the enemy to get closer and possibly within range of the CSC’s surface-to-air missiles (SAM). The CSC’s AN/SPY-7 multi-mission radar is capable of tracking missiles headed towards other ships in its flotilla.

The CSC also provides an enhanced underwater sensing capability. The CSC’s Modular Multistatic Variable Depth Sonar System and S2150-C Hull-Mounted Sonar System allow the ship to navigate through mined sea lanes. The CSC’s can embark the CH-148 Cyclone helicopter, which hosts a suite of sensing equipment to conduct Intelligence, Surveillance and Reconnaissance (ISR) beyond the ship’s horizon. The CSC’s sonar capability, in conjunction with the ASW capable CH-148 Cyclone helicopter, will serve instrumental against PLAN and Beijing-allied submarines, such as North Korea, which can launch long-distance torpedoes and stand-off anti-ship missiles. The RCAF’s anticipated procurement of the P-8A Poseidon maritime patrol reconnaissance aircraft (MPRA), equipped with an outfit of sensing and attack equipment to include magnetic anomaly detectors (MAD), sonobuoys, surface-search radars, and Mark 54 Torpedoes, operating with the CSC will critically enhance ASW capabilities.

These ships also will fulfill the Anti-Surface Warfare (ASuW) mission set that involves targeting enemy ships and aircraft, which would conduct similar adversarial mission sets. The CSC could fulfill the role of a picket, technically the supporting role of being used as a “forward radar observer,” because of its radar and electronic warfare (EW) systems that could mask friendly ships and aircraft by jamming. Through an integrated or combined effort, Canadian or allied P-8As could launch long range anti ship missiles (LRASM) or Rapid-Dragon anti-ship cruise missiles (ASCM), while receiving over-the-horizon (OTH) and midcourse guidance towards their targets from Canadian CSCs. This would allow aircraft and ships in the area to utilize emissions control (EMCON) procedures to remain hidden from Chinese passive electronic intelligence (ELINT) sensors.

Canada is overdue for an upgrade to its submarine fleet. This new fleet should be composed of nuclear submarines capable of deterrence patrols, surveillance, and action across both the great distances and extended deployments required of the Pacific or Canada’s Arctic archipelagic theatre. Theses subs should conduct patrols to avoid a repeat of the lacunae of the Cold War, when the Soviet Union operated submarines through the Northwest Passage undetected. In peacetime and in the lead up to conflict or war, these submarines should conduct intelligence gathering operations including signals intelligence (SIGINT), in conjunction with organizations such as the Canadian Communication Security Establishment (similar to the U.S. National Security Agency), responsible for foreign SIGINT operations.

Operation Ivy Bells is similar example of peacetime SIGINT conducted by the United States during the Cold War. From the beginning of the 1970s until 1981, submarines would transport divers into the Sea of Okhotsk where they then tapped into Soviet undersea communications cables. Despite advances in technology, there is still a distinct operational necessity in regards to using submarines for intelligence collection or observation operations, which would require them to penetrate deep into unfriendly territorial waters, or even sabotage operations in the event of hostilities.


Any military action will have significant implications for Canada’s domestic politics and Ottawa may choose to opt out of certain taskings, especially regarding sentiments of the substantial recently immigrated Chinese-Canadian population. However, aside from the difficulty of politically micro-managing the daily mission of Canadian vessels in a rapidly changing operational theatre, this type of participation avoidance may provoke a critical response from Washington. Worse still, not having sufficient fleet capability to confront the contingencies faced by Pacific allies will leave Canada severely marginalized, with implications for its interests in the Arctic, commerce, and even Canada’s strategic autonomy.

Dr. Julian Spencer-Churchill is associate professor of international relations at Concordia University. He authored Militarization and War (2007) and of Strategic Nuclear Sharing (2014). He published extensively on Pakistan security issues and arms control and researched contracts at the Office of Treaty Verification at the Office of the Secretary of the Navy and then for Ballistic Missile Defense Office (BMDO). He is a consultant that conducted fieldwork in Bangladesh, India, Indonesia, and Egypt. He is a former Operations Officer, 3 Field Engineer Regiment, from the end of the Cold War to shortly after 9/11. Follow him on X (formerly Twitter) @Ju_Sp_Churchill as well as other following links: Publishing 7, Muckrack, Concordia, Canada, Youtube, and the Canadian Centre for Strategic Studies.

Alexandru Filip is an International Relations student at Concordia University, Montreal. He is also an analyst and editor at the Canadian Center for Strategic Studies research institute. His research focuses on strategic and security studies, with a particular interest in naval, air, and nuclear capabilities. He has previously published in RealClearDefense.

Featured Image: The Royal Canadian Navy Halifax-class frigate HMCS Calgary (FFH-335) departs Pearl Harbor, Hawaii (USA), to begin the at-sea phase of Rim of the Pacific (RIMPAC) 2014. (U.S. Navy photo)

RO-RO Ferries and the Expansion of the PLA’s Landing Ship Fleet

By Conor Kennedy

The role of civilian roll-on/roll-off (RO-RO) ferries in a PLA invasion of Taiwan deserves its growing notoriety. With port access secured or coupled with developing logistics over the shore capabilities, RO-RO ferries could deliver significant volumes of forces across the Taiwan Strait, offsetting shortfalls in the PLA’s organic sea lift.1 Some analysts have even described mobilized civilian assets like RO-ROs as a “central feature of [the PLA’s] preferred approach” to a cross-strait invasion.2

But the PLA appears intent on assigning RO-RO ferries to another mission: launching amphibious combat forces directly onto beaches from offshore. The PLA has long lacked sufficient landing ships to deliver its full complement of amphibious assault forces, from both army and Navy Marine Corps forces, in the initial assault landing on Taiwan. Rather than building numerous grey-hulled traditional landing ships, the addition of RO-RO ferries into a combined landing ship fleet could quickly close this gap. 

To make this possible, the PLA has been modifying RO-RO ferries with new stern ramps enabling in-water operations to launch and recover amphibious combat vehicles. The first publicly demonstrated use of the new ramps occurred in 2019 during an exercise involving the 15,560-ton RO-RO ferry Bang Chui Dao, owned and operated by COSCO Shipping Ferry Company and a regular vessel supporting military transportation training exercises. Other ferries have received similar modifications, giving the PLA a significant boost in the total volume of amphibious lift the PLA could muster in a cross-strait amphibious landing.3 This expansion in PLA amphibious capabilities has generated very little attention by the international media despite its clear purpose.

July 2020: A PLAN Marine Corps ZBD-05 loading onto the Bang Chui Dao, featuring a temporarily installed stern ramp that uses hydraulic ram assemblies and hinged preventer stays. (Source: CCTV)
PLAN Marine Corps units in floating embarkation and debarkation training aboard a Type-072A Landing Ship Tank of the Southern Theater Navy in June 2022.4

Amphibious warships are optimized for launching and recovering amphibious combat forces, including swimming armor. They feature well decks closer to the waterline, sometimes submersible, making it easier for forces to launch or recover out of the water. The above image depicts a ZBD-05 approaching the LST Wan Yang Shan’s (No. 995) stern gate and illustrates the challenge of RO-RO ferries in conducting amphibious launch and recovery, which feature freight decks much higher above the waterline that are suited to the height of quay walls. Providing ramp strength that can span that distance requires strong hydraulic rams and stays.   

An army ZTD-05 climbing out of the water up onto the Bang Chui Dao’s vehicle deck via its modified stern ramp. (Source: CCTV-Military Report)

COSCO Shipping Ferry Co., Ltd.

The Bang Chui Dao belongs to COSCO Shipping Ferry Co., Ltd., under the state-owned shipping conglomerate COSCO, which operates ten large passenger RO-RO ferries in the Bohai Gulf. COSCO Shipping Ferry has provided service for PLA transportation support for over 25 years.5 It continues to provide its vessels as a “transport group” (海运大队) of the PLA’s strategic projection support shipping fleet (战略投送支援船队), one of many organized within COSCO businesses and other major commercial shippers to support PLA transportation requirements.6

COSCO Shipping Ferry Co. has been developing capabilities for offshore amphibious launch for its ferries over a number of years. In 2016, the company reported having installed a number of new features into four of its ferries, in response to new national defense requirements. The report suggested the Long Xing Dao and the Yong Xing Dao were among the modified vessels, built in 2010 and 2011 respectively. Noted modifications included rapid egress corridors for personnel and some small equipment, measures in compartment design to resist sinking when damaged, and new hydraulically driven systems to enable greater stern ramp extension for moving amphibious armor on and off the vessel at sea.7

The Yong Xing Dao, Long Xing Dao, Hu Lu Dao and the Pu Tuo Dao have each had their stern ramps upgraded within the past couple of years. These ramps likely utilize the same mechanical principle behind that used for the Bang Chui Dao. Structurally, they appear stronger, longer, and are actuated by heavier-duty hydraulic rams. Noticeably, the ramps are flanked by large, multi-hinged steel support arms that act as preventer stays to maintain ramp rigidity when under tension by the hydraulic rams. These are mounted externally as shown below. The Bang Chui Dao’s ramp-mounted hydraulic assemblies had similar preventers but were mounted internally due to the lack of room between the stern ramp and the quarter-stern ramp.  

Yong Xing Dao with new ramp system installed in July 2022.

Some modified ramp systems will not be permanent installations. For example, recent public footage of the Bang Chui Dao indicates the ramp featured in the 2020 PLAN Marine Corps exercise was removed, and the regular commercial service ramp reinstalled. While suited for launching amphibious armor, the modified system clearly reduced the horizontal clearance of the stern ramp and would not be practical for commercial operators that need to accommodate various sizes of vehicles and trucks. Thus, the PLA likely has these systems held in storage to be installed on vessels like the Bang Chui Dao and the Hai Yang Dao, which features the same quarter-stern ramp, when needed.

Observations of vessel activities also indicate additional COSCO ferries have been similarly modified. In two recent reports, Michael J. Dahm found the Hu Lu Dao took part in amphibious landing training exercises in July 2021, and the Chang Shan Dao in July 2022.8 This implies at least seven COSCO passenger RO-RO ferries have the ability to conduct offshore launch of amphibious combat forces.   

Conversions to BH Ferry Group

Ramp conversion practices have matured enough for wider application in other companies. This is evident within the Bohai Ferry Group, a RO-RO shipping company also concentrated in the Bohai Gulf and comprising the Eighth Transport Group.9

Over the last 15 years, Bohai Ferry Group has expanded its fleet and its cooperation with the PLA.10 The company began implementing national defense requirements in new vessel construction when the former Jinan Military Region Military Transportation Department participated in the design of the 36,000-ton class of ferries starting in 2010 with the Bohai Cuizhu. With inputs from regional military units regarding equipment requirements, the new ferries received helicopter pads, reserve medical spaces, improved command and communications equipment, greater freight deck ventilation, improved firefighting systems and other features.11 While some modifications are difficult to observe directly, some of the latest ramp conversions are readily apparent.

At some point in the last two years, Bohai Ferry Group modified the stern ramps on four of its 36,000 gross-ton ferries, the Bohai Mazhu, Bohai Cuizhu, Bohai Jingzhu, and Bohai Zuanzhu. Specifically, large hydraulic assemblies have been installed on the transom flanking the stern ramp. Similar to the Bang Chui Dao’s assembly, heavy-duty hydraulic cylinders will be released from their secured positions and assisted via a smaller hydraulic ram into a set of clevis brackets affixed to the ramp. As designed, this new position allows for further depression of the ramp into the water, and thus the launch of amphibious combat vehicles.

The Bohai Mazhu in 2017 prior to conversion.
The Bohai Mazhu with new hydraulic assemblies installed in 2022.
A closer view of the Bohai Zuanzhu’s new system.12

These new systems are also operational in recent PLA amphibious exercises, deploying and recovering amphibious forces from offshore, as documented by Dahm. Participation of all four of the 36,000 gross ton class, as well as the 24,777 gross ton multi-purpose ferry Bohai Hengtong was observed in late summer exercises of 2021 and 2022.13 The Bohai Hengtong’s stern ramp is likely long enough for amphibious launch, but may require additional ramp-mounted support due to the presence of the vessel’s quarter-stern ramp. The specific ramp modification for this vessel or its sister ship the Bo Hai Heng Da is unclear.


These modifications to civilian RO-RO ferry ramps have the potential to significantly augment the PLA’s access to amphibious lift. The ferries previously identified contain the following lane in meter (LIM) dimensions and deadweight tonnage (DWT – i.e., a ship’s total carrying capacity) which can help analysts determine the total volume of amphibious combat forces they can add to the PLAN’s organic amphibious lift.

RO-RO Ferries Likely Capable of Offshore Amphibious Launch/Recovery (as of February 2, 2023)

Vessel Name Conversion Method DWT LIM
Bohai Cuizhu (渤海翠珠) Permanent external installation 7,587 2,500
Bohai Jingzhu (渤海晶珠) Permanent external installation 7,598 2,500
Bohai Mazhu (渤海玛珠) Permanent external installation 7,503 2,500
Bohai Zuanzhu (渤海钻珠) Permanent external installation 7,481 2,500
Bohai Hengtong (渤海恒通) Unknown 11,288 2,700
Yong Xing Dao (永兴岛) Permanent installation 7,662 2000
Long Xing Dao (龙兴岛) Permanent installation 7,743 2000
Chang Shan Dao (长山岛) Likely permanent installation 7,670 2000
Pu Tuo Dao (普陀岛) Permanent installation 3,996 835
Hu Lu Dao (葫芦岛) Permanent installation 3,873 835
Bang Chui Dao (棒棰岛) Requires internally-mounted system 3,547 835
Hai Yang Dao (海洋岛) Requires internally-mounted system 3,547 835
TOTAL   79,495 22,040

Note: Most of the modified vessels included in this table have been visually confirmed through openly available imagery and video sources online.

While simply dividing each vessel’s deadweight tonnage by vehicle weights can yield hundreds of vehicles per vessel, the impressive advertised carrying capacities of these ships do not translate directly into the volume of PLA forces they can transport. Crew, passengers, fresh water, fuel, and other various cargo will take up some of the deadweight tonnage listed above, and the remainder will be portioned out to vehicles, as permitted by the total vehicle lane space. Other basic characteristics such as the spacing of vehicle tie down anchor points in vessel decks will also be important factors in determining capacity.     

Internal spatial dimensions and freight deck strength will better determine what kind of vehicle and how many can load. PLA transportation experts find that most of China’s RO-RO passenger ferries feature 3.1-meter wide vehicle lanes, which do not satisfy the width requirements for large numbers of tracked armored vehicles. In addition to not optimizing occupied deck space, improper positioning of heavy loads outside of vehicle lanes could also result in damage to freight decks. Additional internal clearance constraints along ramps and elevators will also limit what types of vehicles and cargo are stowed on each deck, likely only permitting the heaviest armored vehicles, such as main battle tanks, on the main freight decks.14 For example, the four 36,000-gross ton Bohai Ferry Group ferries each have 2,500 total LIM. Despite this impressive volume, PLA experts have noted limitations in their ability to carry large, armored vehicles.

The Bohai Mazhu, the last of the four to enter operation in April 2015, has internal ramp widths of 3.5m and elevator widths of 3m, limiting heavy tanks to only the main freight deck.15 It is likely the Bohai Mazhu’s preceding sister ships also feature the same limiting dimensions. These issues impact transport of the PLA’s heaviest equipment but could also limit their ability to transport amphibious combat vehicles such as the Type-05 series of vehicles. Boat-like in its hull design, a ZBD-05 has a reported width of 3.36 meters and length of 9.5 meters, which could cause difficulty in making turns and accessing upper or lower decks.16 Other vessels may be more accommodating. For example, the Chang Shan Dao reportedly has a 3.6 m-wide elevator and 3.5 m-wide internal ramps, as may its sister ships, the Yong Xing Dao and Long Xing Dao.17

More importantly, while total loading capacities may be useful for gauging how the PLA might optimize its loading plans for relatively secure terminal to terminal delivery operations, offshore amphibious launch entails very different considerations. The stowage of amphibious combat forces will likely be done according to combat loading plans that do not emphasize the maximization of forces occupying deck space. Instead, forces would load according to their assigned assault waves, which likely include both armor and infantry aboard assault craft, and other support elements. Each wave must be positioned and readied to access and launch from the vessel’s stern ramp.

Moreover, launching amphibious combat forces brings vessels closer to active combat areas. The threat of adversary attacks could lead the PLA to disperse forces across many ships. Multiple units confined to a single ferry could be a vulnerability demanding more protection of that single vessel. It is likely that ferries participating in this mission will not be loaded to the brim. As pure transporters, they may seek to launch forces as quickly as possible to reduce their own exposure and swiftly return to ports of embarkation to load follow-on forces.

Despite this, these vessels offer a significant additional source of amphibious lift for the PLA, especially for delivery of first echelon amphibious combat forces critical to securing areas for landing the follow-on invasion force. With the previously-mentioned spatial limitations in mind, a conservative estimate of the total capacity of the ships identified in this article adds on capacity sufficient for half the PLA army’s primary amphibious combat forces (12 amphibious combined arms battalions).18 This places one battalion on each vessel, with room for additional supporting elements from their respective brigades. Depending on internal space constraints, vessels like the Pu Tuo Dao could probably deliver a single battalion, while some of the larger vessels could likely carry up to two battalions if the PLA accepts the risk. Having fewer forces embarked would also make it easier for these vessels to support forces loaded well in advance of an invasion, as many ferries market to tourists their berthing compartments complete with toilets and showers, and feature mess halls and recreational facilities. Spare vehicle deck space could also be employed to support embarked amphibious units. If done right, such early loading could relieve pressure on PLA loading operations, but also make detecting a force build up more difficult.     


The PLA has rapidly expanded its landing ship fleet over the last few years. It has not taken the form many may have expected, such as the construction of numerous naval landing ships, instead focusing efforts on civilian RO-RO ferries to fulfill the PLA’s requirements. This article set out to identify the PRC-flagged RO-RO ferries with ramps that can enable offshore amphibious launch. It has likely failed to enumerate all the various ramp configurations and identify all the vessels involved.

Both COSCO Shipping Ferry Group and Bohai Ferry Group have ferries capable of supporting this mission. Some ramp systems are temporary, suggesting preparations for some ferries to rapidly refit when needed, while others are permanent observable installations. The ferries themselves are dual-commercial and military use ships, however, their ramp modifications have a sole purpose, the offshore launch of amphibious combat forces in a landing operation against Taiwan. Furthermore, these capabilities are not simply theoretical, as some of these ships take part in landing exercises with PLA amphibious ground units.  

The PRC appears to have significantly expanded its amphibious lift capacity with little notice from the international community, much less criticism. While many PLA experts write openly on the important roles of the commercial RO-RO fleet in a cross-Strait invasion, specifically their roles in transporting large volumes of heavy follow-on forces, they have generally steered clear of discussing their role in offshore amphibious launch. If these RO-RO modifications and their application in military exercises are observable by a foreign audience, they should be readily known by PLA military transportation professionals. This supports the author’s original assertion in 2021 that this expansion in capacity could occur quickly and quietly.

There are still many more questions to be answered regarding the effectiveness of this approach. The PLA must tackle coordination between the joint forces, including organic landing ships and civilian assets. There are organizational, command and control, communications, security, and numerous other issues to solve before RO-RO ferries can effectively support a joint island landing campaign, especially if they are to join in delivering landing assault waves. Nonetheless, an initial understanding of the scale of this approach is important for gauging the significance of its contribution toward delivering the PLA’s joint landing forces.

Conor Kennedy is a research associate in the U.S. Naval War College’s China Maritime Studies Institute in Rhode Island.

The analyses and opinions expressed in this paper are those of the author and do not necessarily reflect those of the U.S. Navy or the U.S. Naval War College.


1. For an analysis of a PLA invasion against port locations, see: Ian Easton, Hostile Harbors: Taiwan’s Ports and PLA Invasion Plans,” Project 2049 Institute, July 22, 2021,; For an analysis of PLA logistics over the shore capabilities, see: Dahm, J. Michael, “China Maritime Report No. 16: Chinese Ferry Tales: The PLA’s Use of Civilian Shipping in Support of Over-the-Shore Logistics” (2021). CMSI China Maritime Reports. 16.; and “China Maritime Report No. 25: More Chinese Ferry Tales: China’s Use of Civilian Shipping in Military Activities, 2021-2022” (2023). CMSI China Maritime Reports. 25.

2. Henley, Lonnie D., “China Maritime Report No. 21: Civilian Shipping and Maritime Militia: The Logistics Backbone of a Taiwan Invasion” (2022). CMSI China Maritime Reports. 21.

3. Conor Kennedy, “Ramping the Strait: Quick and Dirty Solutions to Boost Amphibious Lift,” China Brief, Volume 21, Issue: 14,

4. 严家罗, 周紫春, 周启青 [Yan Jialuo, Zhou Zichun, Zhou Qiqing], 海军陆战队某旅海上浮渡装卸载训练 [“A Navy Marine Corps Brigade in Afloat Loading and Unloading Exercises”], 当代海军 [Navy Today], No. 7, 2015, p. 31.

5. 潘诚, 王正旭 [Pan Cheng, Wang Zhengxu], 沈阳联勤保障中心某航务军代处与企业共同制定军运细则 [“A Shenyang Joint Logistics Support Center Navigational Military Representative Office Jointly Formulates Military Transportation Rules with an Enterprise”], 中国国防报 [China Defence News], June 15, 2017, p. 3,

6. Conor M. Kennedy, “China Maritime Report No. 4: Civil Transport in PLA Power Projection” (2019). CMSI China Maritime Reports. 4.

7. 王正旭, 高勇, 贾文暄 [Wang Zhengxu, Gao Yong, Jia Wenxuan], 客轮首尾开门运兵运超重军事装备 可起降直升机 [“Passenger Ships Carry Troops and Overweight Military Equipment, and Can Land Helicopters”], 中国国防报 [China Defence News], September 29, 2016,

8. Dahm, J. Michael, “China Maritime Report No. 16: Chinese Ferry Tales: The PLA’s Use of Civilian Shipping in Support of Over-the-Shore Logistics” (2021). CMSI China Maritime Reports. 16. pp. 33-38,; Dahm, J. Michael, “China Maritime Report No. 25: More Chinese Ferry Tales: China’s Use of Civilian Shipping in Military Activities, 2021-2022” (2023). CMSI China Maritime Reports. 25. Pp. 34-36,

9. 李远星, 王丙 [Li Yuanxing, Wang Bing], 新时代战略投送支援力量建设运用研究 [“Research on Construction and Use of Strategic Projection Support Forces in the New Era”], 国防 [National Defense], No. 12 (2017), 20–23.

10. Since 2006, Bohai Ferry Group has constructed over 16 large RO-RO ferries ranging from 20,000 to 45,000 gross tons. See: 关于我们 [“About Us”], 渤海轮渡集团股份有限公司 [Bohai Ferry Group Co., Ltd.], Undated,

11. 李响 [Li Xiang], 军民融合领域的一次成功实践: “渤海翠珠” 滚装船提升我军海上战略投送能力纪实 [“Record of a Successful Practice in Civil-Military Fusion: the RO-RO Ship ‘Bohai Cuizhu’ Enhances Our Military’s Maritime Strategic Projection Capabilities”], 国防科技工业 [National Defense Science and Technology Industry], No. 1 (2012), 53.

12. 建设打仗后勤 [“Building Warfighting Logistics”], CCTV –《追光》[CCTV- Chasing the Light], Episode 11, October 9, 2022,

13. Dahm, “China Maritime Report No. 16,” pp. 33-39; Dahm, “China Maritime Report No. 25,” pp. 36-44; For an image depicting the Bo Hai Heng Tong launching vehicles, see: H I Sutton and Sam LaGrone, “Chinese Launch Assault Craft from Civilian Car Ferries in Mass Amphibious Invasion Drill, Satellite Photos Show,” USNI News, September 28, 2022,

14. 孙琪, 刘宝新 [Sun Qi, Liu Baoxin], 民用客滚船军事应用研究 [“Research on Military Application of Civil Ro-Ro Passenger Ships”], 军事交通学报 [Journal of Military Transportation], No. 2, 2022, p. 26.

15. Ibid.

16. “ZBD-05 or VN-18,” Army Recognition, July 9, 2021,;

17. 吴克南 [Wu Kenan], 我国滚装船运输军事重装备的适用性研究 [“The Applicability Research of China Ro-Ro Ship Used to Transport Military Heavy Equipment”], 大连海事大学-硕士学位论文 [Dalian Maritime University – Master’s Thesis], March 2016, p.

18. This is based on the estimated size of an army amphibious combined arms battalion consisting of 80 vehicles and 500-600 troops. See: Blasko, Dennis J., “China Maritime Report No. 20: The PLA Army Amphibious Force” (2022). CMSI China Maritime Reports. 20, pp. 3-4.

Featured Image: A CCTV report showed a cargo ship that was being used to carry troops, weapons and supplies in a recent PLA exercise. (Photo via CCTV)

Distributed Maritime Operations – A Salvo Equation Analysis

By Capt. Anthony Cowden, USN (ret.)

A recent article published by the Center for International Maritime Security (CIMSEC) – the first in a series – does an outstanding job of describing and explaining the Navy’s “core operating concept” of Distributed Maritime Operations (DMO). In short, DMO calls for “…the massing and convergence of fires from distributed forces, complicating adversary targeting and decision-making, and networking effects across platforms and domains.”1

The strike effectiveness of the DMO operating concept requires further investigation. In pursuing this, it is important to recall that a fleet does four things – it Scouts, it Screens, it Strikes, and it Bases.2 As currently envisioned, at least in open source definitions, DMO is not yet well-developed in the Scouting, Screening, and Basing functions of a fleet. Rather, DMO seems mostly focused on the offensive functions of a fleet, the Strike function.

The first step in this analysis will be to analyze a traditional concentrated force versus another concentrated force using the salvo equations. The second step will be to look at a distributed force that is able to mass fires against a concentrated force. The final step will be to look at a concentrated force that engages part of a distributed force. We will also look at what “firing effectively first” means in practice, and what happens if the enemy force distributes.

The Salvo Equations

The salvo equations were developed by the late Captain Wayne Hughes and are discussed in detail in Chapter 1 and Appendix A of Fighting the Fleet: Operational Art and Modern Fleet Combat. With the salvo equations, Captain Hughes showed:

“how modern naval combat follows a salvo model: opponents apply a pulse of combat power to each other in an instantaneous salvo exchange. A salvo exchange is an interaction of offensive combat power (e.g., mines, torpedoes, bombs, or missiles) and defensive combat power (e.g., surface-to-air missiles [SAMs], jamming, chaff, decoys). Combat power remaining from these interactions is applied against a target’s staying power (the number of hits of a particular weapon that a target can withstand and still be useful for combat purposes).”3

The salvo equations are presented here for reference:

Concentrated versus Concentrated

The first step in our analysis will be to look at two concentrated forces engaging one another. To simplify the analysis, it is assumed that each force is exactly equal, where each force consists entirely of the same number of missile-equipped surface ships, with the same offensive and defensive capabilities. These include:

  • Each force consists of six surface ships (A = B = 6).
  • Each surface ship has a displacement of 8,000 tons. Using the “cube root rule,” this means that it takes two “thousand-pound bomb equivalents” (TPBEs) to put a ship out of action. Given the destructive force of modern explosives, that equates to 2 x 660 lbs, or 1,320 lbs of modern warhead explosives. Assuming a warhead size of 500 lbs, it would take 2.64 warheads to put an 8,000 ton ship out of action. (a1 = b1 = 2.64).4
  • Each surface ship is equipped as follows:
    • Eight anti-ship cruise missiles (ASCMs) equipped with a 500 lb warhead. All ASCMs are considered to be “well-aimed” (i.e., unless otherwise destroyed, decoyed, or defeated, the ASCM would hit its intended target; this is not always true, as discussed in Chapter 1 of Fighting the Fleet.5 b = ).
    • A surface-to-air missile (SAM) system capable of destroying two incoming ASCMs in a general engagement involving multiple incoming missiles.
    • A close in weapons system (CIWS) capable of destroying two incoming ASCMs.
    • An electronic countermeasure system (ECM) capable of defeating one ASCM.
    • A decoy system capable of defeating one ASCM.
    • Therefore, given the combined capabilities of the SAM, CIWS, ECM, and decoy systems to destroy or defeat incoming ASCMs, a3 = b3 = 6.
  • Each force has equivalent organic and inorganic scouting capabilities, and is able to detect and localize the opposing force at the maximum range of their ASCMs.

Based on these assumptions, the salvo equations for an engagement between two concentrated forces are featured in Figure 1:

Figure 1.

Predicting damage to warships in combat is always difficult, but a change in the number of units in force A and B () of 4.55 indicates enough hits to put 4.55 ships out of action in each force.6 Of course, this is highly dependent on hit distribution, which, if evenly distributed across the force, would mean that each ship in each force received some damage, but was not put out of action. In addition, this scenario assumes that each force was able to launch an attack “simultaneously,” where simultaneity is defined as each force being able to launch its ASCMs against the other force before it is hit by the other force’s ASCMs.

The essence of Captain Wayne Hughes’s admonition to “fire effectively first” then is to launch an attack and have missiles hit the opposing force before that force can launch its missiles.17 Assume that if force B was able to “fire effectively first,” then proceeding from the salvo equations above, force A would be reduced by a total of 4.55 ships, so force A’s subsequent attack on force B would result in the following:

Figure 2.

A negative number for DB indicates that the B force is likely to be able to defeat all of force A’s incoming missiles; and the bigger the number, the more likely it will defeat the incoming strike. Such is the advantage of being able to “fire effectively first.”

This highlights two other aspects of offensive and defensive fires. First, close-range defensive fires such as point-defense missiles can often be replenished prior to another salvo attack. While they may be limited in their ability to defeat an incoming salvo, they can generally be reloaded and prepared to defend against a future salvo, without any reduction in capability. Second, this is not always true of ASCMs, many of which are housed in dedicated launchers and are limited in number and cannot be reloaded quickly or at sea. As the reader will see in this example, there is arguably little incentive to retain offensive fires for possible future engagements, as it often takes all the offensive firepower available to overcome the opponent’s defensive capability.

Distributed versus Concentrated

The second step in this analysis is to look at a distributed force that is able to mass its fires against a concentrated force. However, at this point the reader should be able to see that the results are likely to be similar as in the scenario presented above, assuming that the concentrated force is able to launch against all elements of the distributed force. An issue associated with the distributed force is the coordination required for a distributed force to mass its fires against a common target. Scouting information about target location, course, and speed would need to be communicated to all elements of the distributed force, and some sort of coordination and communication would need to occur for the distributed elements to mass their fires against the target. This is inherently more complex than attacking with a concentrated force, and more subject to communication and coordination failure.

The third step in this analysis is to look at a concentrated force that engages part of a distributed force. The danger in distributing one’s own force in the face of a competent – or lucky – opponent is that the opposing force will defeat one part of own force “in detail”; that is, the entire opposing force will engage just part of own force and be able to destroy it. Assuming that force A divides itself into two equal parts, A(1) and A(2), and assuming that force B engages A(1) before A(2) can become involved in the fight, such an engagement is characterized in the salvo equations as depicted in Figure 3:

Figure 3.

Here we see that force B has a preponderance of offensive firepower that overwhelms A(1)’s defensive capability, and force B’s defensive capability is able to defeat force A(1)’s inadequate offensive punch. Should A(2) get off a shot against force B, its results would look exactly like those of force A(1), as shown in Figure 4:

Figure 4.

The net result of the damage to force A in the distributed case would be the likely destruction of all three A(1) ships, with no damage to the opposing A(2) ships. Recall that in the concentrated case, the damage to force A ships (i.e., 4.55 put out of action) would be distributed over the six ships of the force. Here, however, enough offensive power from force B to put 11.36 ships out of action would only be distributed over the three ships of force A(1), virtually ensuring that all three ships would be put entirely out of action. Force B would not suffer any damage at all. Compare this to the concentrated case or the case where a distributed force A had been able to mass its fires (Figure 1), where force B would have suffered an equal amount of damage.

What happens if force B only detects one of the distributed parts of force A (force A(1)), but distributed force A is able to mass its fires against force B?

Figure 5.

The result is depicted in Figure 5. All three ships of force A(1) would likely be put out of action, no damage would be incurred by force A(2), and force B would incur the same damage as if force A were concentrated. It turns out this is the one case where a distributed force has a strike advantage over a concentrated force. However, it should be noted that this is not an advantage conferred by distribution, it is an advantage conferred by effective Screening and Scouting. One part of the distributed force drew the attention and the fire of the concentrated force, but was able to combine its fires with the undetected portion of the distributed force.8

Next, what would happen if force B knew that force A had distributed itself, it had detected force A(1), and it assumed that force A(2) was nearby? If it retained half of its ASCMs for a possible future engagement with force A(2), the engagement with A(1) might look like the results contained in Figure 6:

Figure 6.

Of course, a future engagement with force A(2) would look much the same, and note that force B does not suffer any damage. Given the uncertainty of combat, it makes much more sense for force B to launch all of its ASCMs against force A(1), likely destroying all of force A(1), and use screening to scuttle back into port before any other force can attack it – a classic case of Corbett’s “arrested offense.”

“Fire Effectively First!”

In Figure 2, the value of firing effectively first was illustrated for the base case of two concentrated forces engaging one another. This also applies to a concentrated force and a distributed force that engage each other simultaneously. The following looks at the value of “firing effectively first” for two of the other cases discussed previously:

  • A concentrated force that engages part of a distributed force (Figure 7). It should be self-evident that if the concentrated force, B, fires effectively first, the engaged part of the distributed force will be put out of action. But what happens if the part of the distributed force A(1) fires effectively first against the concentrated force B, and then B launches an attack on A(1)? As we can see in the following equations, B is able to defeat A(1)’s incoming salvo, and since it is undamaged, if it is able to launch an attack against A(1), it will overwhelm A(1)’s defenses.
Figure 7.
  • A concentrated force only detects one of the distributed parts of force A (Figure 8). In this case, force B fires effectively first against force A(1), which is put out of action, and force A(2) launches a retaliatory strike against force B. A(1) is destroyed, and force B is able to defeat A(2)’s inadequate attack.
Figure 8.

Whether a force distributes or not, what is essential to victory – and survival – is the ability to “fire effectively first,” and firing effectively first is a function of scouting, not distribution or concentration of platforms. That being said, even if the distributed force fires first, it will be unable to defeat or even damage the concentrated force unless it can effectively coordinate its attack.

What if the Enemy Distributes?

If distribution is a good idea, then we must expect the other side to distribute as well. The combinations of possible engagements begin to escalate quickly, depending on how each side distributes its forces. We can, however, look at some of the more interesting cases, based on the assumption that each side distributes evenly into two equally-sized groups of three ships:

  • Both forces are able to launch coordinated attacks on each other near-simultaneously. The results will be the same as those depicted in Figure 1. Both sides being distributed provides no advantage to either side in terms of strike.
  • One force is able to attack one part of the other force, but the entire other force is able to attack both parts of the first force. The results will be the same as those depicted in Figure 5. Both sides being distributed provides no advantage to either side in terms of strike.

These dynamics yield a set of recommendations, including:

  • No matter how forces are deployed – concentrated, distributed, or some other way – win the scouting contest and “fire effectively first.”
  • If forces are distributed but the communications capability is not able to coordinate their fires, then force posture must be rearranged to respect the limits of communication. If this cannot be done in time, then better to disengage to fight another day.
  • Improve screening. Decoys, for example, can be very useful in diluting the effect of the enemy’s salvo. The effect of each ship in force A being able to decoy just one more missile each is shown in Figure 9: it effectively halves the amount of damage force A could expect to receive.
Figure 9.


The salvo equations are analytical tools, not predictive ones. They do not result in “the answer” as to exactly how any single engagement will turn out. Combat entropy and instability, discussed at length in Fighting the Fleet, is a factor worth appreciating, such as how six bombs sunk four carriers at Midway, but five kamikazes did not sink one destroyer, USS Laffey, at Okinawa.9 That being said, the salvo equations can be used as an analytical tool to provide insight into probable outcomes. As they say, the race does not always go to the fastest, or the contest to the strongest, but that is the way to bet.

It should be noted that the single point of failure for a distributed force is the ability to coordinate a strike on another force. This coordination becomes even more complex with greater distribution of one’s own force, and even more so when the other force is distributed.10 If the distributed force cannot coordinate their fires then they lose in every scenario. This may be caused by jamming or some other interruption of communications, but it could also be from any failure to efficiently coordinate a strike, which could be as simple as poor distribution of weapons, training shortcomings, and other shortfalls.

The one case where a distributed force comes out ahead of a concentrated force is the case where only one part of the distributed force is detected by the enemy and absorbs the enemy’s attack, but is able to combine its strike with the other part of the distributed force before it dies. But that is not a “concept of operation,” it is more of a scouting tactic, and in prior generations this was better implemented with a LAMPS Mk III, Hawklink, and the naval tactical data system (NTDS).

DMO might be able to “complicate adversary targeting and decision-making” and it should be noted it would apply to one’s own force if the enemy distributes as well. But when it comes to the Strike function of a fleet, a distributed force had better be able to efficiently mass its offensive fires, or it runs the risk of being defeated in detail, resulting in, at best, a disappointing exchange in the number of destroyed and damaged ships.

Anthony Cowden is the Managing Director of Stari Consulting Services, co-author of Fighting the Fleet: Operational Art and Modern Fleet Combat, author of The Naval Institute Almanac of the U.S. Navy, has published numerous articles on a range of topics, and was a commissioned officer in the U.S. Navy for 37 years.


[1] Filipoff, Dmitry, Fighting DMO, Pt. 1: Defining Distributed Maritime Operations and the Future of Naval Warfare, Center for International Maritime Security, February 20, 2023,

[2] Cares, Jeffrey R. and Anthony Cowden, Fighting the Fleet: Operational Art and Modern Fleet Combat (Annapolis, MD: Naval Institute Press, 2022), pp. 71-73

[3] Cares and Cowden, p. 16

[4] Cares and Cowden, p. 23. Estimating the number of hits to put a ship out of action is probably the most controversial aspect of using the Salvo Equations. The reader is invited to substitute whatever value they desire and conduct the analysis themselves. One useful approach is to use a parametric range of values and discover the sensitivity of the force to the number of hits required.

[5] Cares and Cowden, pp. 19-22

[6] How to interpret the Salvo Equations, as well as the concept of “Combat Entropy”, is discussed extensively in Chapter 1 of Fighting the Fleet.

[7] Hughes, Captain Wayne P., USN (Ret.) and Rear Admiral Robert P. Girrier, USN (Ret.), Fleet Tactics and Naval Operations, Third Edition (Annapolis, MD: Naval Institute Press, 2018), Chapter 13.

[8] Quick show of hands: who wants to serve in force A(1)?

[9] Cares and Cowden, pp. 19-22

[10] Distributed networked operations can become amazingly complex. Those interested in the theory and application of distributed network operations are invited to read Cares, Jeff. Distributed Network Operations: The Foundations of Network Centric Warfare. Newport, RI: Alidade Press, 2005.

Featured Image: Amphibious assault ship USS Bonhomme Richard (LHD 6) fires a NATO Sea Sparrow surface-to-air missile to intercept a remote-controlled drone as part of Valiant Shield 2016 (VS16). (U.S. Navy photo)