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Manning the Unmanned Systems of SSN(X)

March 16, 2022 Guest Author Leave a comment

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 21^st 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:

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.
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.
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 5^th 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 5^th 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)

December 7, 2021 Guest Author 4 Comments

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
UUV Crew	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.

Appendix 1: Analysis Constraint Equations

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 7. Crew Availability Equation

Equation 8. Charge Availability Equation

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.

Capability Analysis

Time to Re-Task, Downsize, and Re-Engineer the SSN, Part II

June 26, 2019 Guest Author Leave a comment

Read Part One here.

By Duane J. Truitt

As discussed in Part I, it is clear that NAVSEA needs to undertake a project now to completely re-engineer the next generation of SSNs. The old bloated SSN(X) (now “New SSN”) concept should be rejected entirely because it is more of the same, but bigger and more expensive. Instead, the Navy should go for a new class of SSN that is far smaller and cheaper than the current Block 5 Virginias.

The key components of a reimagined, redesigned “compact” SSN include four major changes from existing SSN designs. Namely, it can refocus the SSN and its systems on its original roles of anti-shipping and ISR, eliminating the vertical launch tubes and enhancing the horizontal launch tube systems. It can re-engineer the nuclear power plants to result in power plants that are safer, simpler, more compact, and cheaper to build and operate. It can also re-engineer the rest of the SSN systems to increase automation, optimize crew work processes, and to reduce the total required ship’s complement. Finally, it can modernize and revise the SSN’s weapons system to provide a wider range of weapons capability and increase the number of warshots deployable in a compact hull form

The net result of the proposed changes should be a more effective, more capable, yet smaller and cheaper SSN that the U.S. Navy can afford to build and operate in numbers sufficient to meet existing and growing near-peer naval challenges of the mid-21^st century. Such a submarine would be expected to displace well under 5,000 tons.

In recognition that major ship class redesigns with “great leap forward” technology improvements carry additional development risk and incur longer development timeframes, it is good practice for the Navy to pursue these advances in a relatively small block build or in technology insertion increments (as used on the Virginia-class boats).

The proposed Next Gen “New SSN” class should consist of the following minimum of two blocks.

Block I

Set an overall objective for Block I to build a new SSN of not more than 4,500 tons, but less if feasible, and a crew size of not more than 70 officers and sailors, and less if achievable. The design should strive to reduce the volume of operations spaces, engineering spaces, crews’ quarters, storage, and support spaces accordingly. Total construction cost should aim for significantly less than $2 billion each in 2019 dollars.

The ship should include a new secondary propulsion plant system utilizing hybrid drive – i.e., eliminating the main propulsion turbines and reduction gears, and utilizing only two relatively large turbo-generators with electric drive, as used on the Colombia SSBN class design. This design provides a significant noise reduction and propulsion plant size reduction. It can also consider using a shrouded propulsor with built-in electric motor external to the pressure hull. The new design can include a new reactor plant with next-gen automation and design simplification, as a scaled-down version of the USS Gerald R. Ford A1B plant design.¹Consider, and develop as available, alternatives to conventional lead acid battery banks for emergency power generation, including use of next-gen hydrogen fuel cells and/or advanced battery technology to increase power availability in event of a prolonged reactor shutdown, and/or to provide enhanced quiet operations for limited periods of time.

The new design should retain the standard 21-inch torpedo tubes for use with heavyweight torpedoes (Mk 48 ADCAP) and submarine launched cruise missiles (i.e., Maritime Tomahawk ASCMs, Naval Strike Missiles, etc.) relevant to surface ship attack. It should also add new 13-inch torpedo tubes to deploy Mk 46/54 lightweight torpedoes relevant to ASW. This will result in an overall increase in the number of warshots that a submarine can carry per unit hull volume. The design should also include next generation torpedo defenses including both towed passive softkill systems and hardkill kinetic weapons with respective launch tubes, as already in use on surface combatants.

Eliminate the vertical launch tubes. For those who say the Navy still cannot afford to give up the deep strike land attack mission (because of now-obsolete fears of naval irrelevance in 21^st century warfare), we still have all of the existing Virginia-class boats that already have been delivered, and those that have already been ordered, including those Block 5s with VPM – which still provide a robust deep strike land attack capability in the SSN fleet today and for the next 40 years. If it is really thought necessary that the Navy provide the deep strike land attack capability from submarines, then build new SSGNs to provide that capability starting in the early 2030s as the existing SSGNs retire– that mission, however, does not require SSNs as platforms. If there is any resulting temporary “gap” in needed launchers it may be filled with surface warships and aircraft.

To be ready for unmanned systems and networked warfighting capabilities the new design should account for modularity and open architecture in submarine system interfaces (communications and combat data management systems) to enable effective networking with off-ship platforms including unmanned undersea vessels (UUV), unmanned surface vessels (USV), and aircraft, both manned and unmanned. Submarine systems must be interoperable within the evolving architecture of Naval Integrated Fire Control – Counter Air (NIFC-CA) and Cooperative Engagement Capability (CEC), and be flexible within the Navy’s Distributed Maritime Operations (DMO) doctrine.

Block 2 – Next-Gen Reactor Plant Technology Insertion

While developing and building the Block 1 new SSN, the Navy can launch a new reactor design program to adapt a generation four reactor plant to provide numerous advantages for naval submarine power over current technology pressurized water reactor (PWR) plants. Perhaps the most likely candidate is a molten salt reactor (MSR)², which is part of the current crop of commercial generation four reactor plants already under development in the U.S. and elsewhere including the People’s Republic of China. Liquid MSR technology, in experimental reactor use since the 1960s, has several advantages over PWR plants. The reactor does not have a solid “core” that requires replacement in order to refuel the reactor, and the reactor can be refueled at will during regular maintenance availabilities. It also does not require cutting open the pressure hull or making other intrusive openings to the plant to “gas up.” This design still delivers extremely long endurance between refueling operations, and results in a significant reduction in hull lifetime operating cost. It also provides extended hull operating lifetime without enlarging the hull to accommodate a larger reactor plant needed to yield a life-of-ship reactor.

MSR reactors are intrinsically safe unlike PWRs (there is no meltdown risk because the reactor itself, along with its fuel, is already molten), thus significantly reducing the safety requirements and operating limitations necessary with PWRs. MSR reactors also operate at one atmosphere of pressure, eliminating the need for very heavy steel reactor pressure vessels and primary coolant system components, thus significantly reducing the weight and size of the nuclear power plant. This greatly reduces the effects of thermal stress due to rapid cooldown associated with thickly walled steel pressure vessels.

MSR reactors operate at far higher temperatures than PWRs, thus allowing the use of more efficient high temperature steam secondary plants, reducing both the size and weight of the secondary plant. This also yields a much higher overall thermal efficiency for the entire power plant, meaning that a MSR plant of a given capacity in MW thermal power (MWt) produces the same motive power as a much larger PWR plant.

MSR reactors do not need high speed main coolant pumps as do PWRs, hence are intrinsically quieter than today’s submarine power plants. MSR reactors can use a wide variety of cheaper and more widely available reactor fissionable fuels, including, amazingly enough, spent fuel from conventional PWRs, lower enriched uranium fuel, depleted uranium, and thorium. When the MSR fuel is completely spent and discarded as waste, it is far less radioactive over far shorter decay timeframes than spent fuel from conventional PWRs.

Overall, MSR reactors are significantly safer, smaller, lighter, simpler, more efficient, and cheaper than PWRs – all of which will contribute significantly to reducing the size and cost (both construction, and operating) of next gen SSNs. The end result of a successful integration of MSR technology into SSNs will be a much more compact, simplified, and capable sub in addition to being much less costly to build and operate.

This investment in a new nuclear propulsion technology approach will undoubtedly generate lots of pushback. People, including professionals, find comfort with the familiar, and more people than not simply dislike change because it creates uncertainty. However, nuclear propulsion itself was perceived as a big threat to the status quo by many senior leaders in the fleet and at Pentagon in the late 1940s and 1950s when Admiral Rickover upset their apple carts. Rickover managed to keep his program operational and funded by going over the heads of the senior uniforms, and cultivated “protection” from the senior uniforms via senior members of Congress who controlled naval budgets and authorizations for ship construction.

Rickover actually considered several alternative technology approaches before finally settling on a single approach via PWRs. His team developed a liquid sodium cooled reactor plant, or “Liquid Metal Fast Reactor” (LMFR) first as a prototype (S1G) in West Milton, New York, and then installed the reactor (S2G) in a SSN, the USS Seawolf (SSN-575). These liquid metal reactor plants enjoyed several but not all of the same advantages listed above for MSR plants, but also suffered significant limitations particular to liquid sodium that are not issues with MSR plants, including a tendency to leak, and the fire hazard presented by such leaks of liquid sodium metal. This reactor design was abandoned in 1956, and the liquid sodium reactor in Seawolf was later replaced with a PWR reactor. But today’s fourth generation MSR technology is both very different from and more advanced than that used in the early liquid sodium plants.

It is clearly time for Naval Reactors to give MSRs a very hard look, including designing, building, and operating a prototype. If it works out well, then design one into the second or a subsequent block of the new SSN submarines, likely by the late 2020s to early 2030s. It would likely result in a smaller displacement hull with greater capability, quieter, and lower cost to build and operate than those based on traditional PWR propulsion technology. Even if MSRs are not able to deliver all that is expected, there are other fourth generation reactor technologies that may be feasible. Even a next generation LMFR may be worth reconsideration, given what we know now that Admiral Rickover and his team at Naval Reactors did not know in the mid-1950s.

Conclusion

This block development approach to a new SSN, a next generation of smaller, more capable, and far cheaper to build and operate SSNs, will lead the U.S. Navy to building a numerically larger yet more capable SSN force. Instead of the age old “capacity vs. capability” argument between opposing sects of naval planners and advocates, the result will be both much more capacity and more capability. The proposed smaller, cheaper, yet more capable sea-control focused attack SSNs will help the U.S. cost-effectively meet the immediate and growing threat of peer naval adversary submarine fleets today and for decades to come.

Mr. Truitt is a veteran Cold War era SSN sailor, qualified nuclear reactor operator, and civilian nuclear test engineer as well as a degreed civil engineer, environmental scientist, and civil/environmental project manager with extensive experience at both naval and civilian nuclear facilities as well as military and civilian facilities development. His interest today as an author is in forward looking military preparedness and improvements in both capacity and capability of U.S. naval forces.

Endnotes

1. A1B Reactor; https://www.globalsecurity.org/military/systems/ship/systems/a1b.htm

2. Albert J. Juhasz, NASA Glenn Research Center, Cleveland, Ohio 44135; Richard A. Rarick and Rajmohan Rangarajan Cleveland State University, Cleveland, Ohio 44115; “High Efficiency Nuclear Power Plants Using Liquid Fluoride Thorium Reactor Technology; https://ntrs.nasa.gov/search.jsp?R=20090029904 2019-04-02T18:59:43+00:00Z

Featured Image: Virginia-class submarine USS Missouri. (General Dynamics Electric Boat photo courtesy of Edward S. Gray, Secretary, Missouri (SSN-780) Commissioning Committee.)

Capability Analysis

Time to Re-Task, Downsize, and Re-Engineer the SSN, Part 1

June 19, 2019 Guest Author 14 Comments

By Duane J. Truitt

The U.S. Navy is faced with several big challenges in maintaining undersea warfare dominance – the domain of the fast attack nuclear submarine or “SSN.”

These challenges include the reemergence of a near peer naval threat that is a direct challenge to the entire U.S. Navy, including our SSN force. The current and growing undersea threat includes both advanced technology attack submarines (including nuclear, diesel-electric, and air independent propulsion variants) with advanced torpedoes and cruise missiles, and much increased numbers of adversary submarines, particularly in the Indo-Pacific theater. Another challenge comes from the rapidly escalating procurement and sustainment costs of ever-larger and more complex U.S. SSNs since the end of the Cold War.

These two challenges have resulted in a very large immediate deficit in U.S. SSN numbers,¹ if not capabilities, that is expected to continue for decades. The Navy’s current planned way out seems to be to simply hope for the best, that the funding will materialize to build many more of today’s very large and expensive SSNs. That plan is increasingly seen as unlikely if not impossible given existing serious constraints on U.S. defense spending.

This situation is not unique to the submarine force. The Navy’s overall force structure assessment (FSA) is undergoing a significant revision due for release later this year.² Navy leaders including outgoing CNO ADM John Richardson and VADM Bill Merz have stated on multiple occasions that the surface fleet is going to evolve with many more small surface combatants, with enhanced capabilities, and many fewer large surface combatants. Admiral Merz stated:

“You may see the evolution over time where frigates start replacing destroyers, the Large Surface Combatant starts replacing destroyers, and in the end, as the destroyers blend away, you’re going to get this healthier mix of small and large surface combatants.”

What is driving this mix to an overall surface fleet weighted toward smaller vessels? Cost. The cost to build, and then the cost to operate and maintain vessels is necessitating this shift from the current generation of surface warships dominated by large surface combatants. The same cost factors also inhibit submarine construction and operations, too. This is in fact a rebalancing in the age-old naval argument of capability versus capacity. The rebalancing is made possible by emerging technologies that allow the Navy to package enhanced capability into smaller hull forms, and to take advantage of new capabilities in cheap yet capable unmanned vessels. Yet today, the U.S. Navy still has no “small subsurface combatant” – just the very large Virginia-class SSNs that are evolving into even larger and more expensive hulls with the Block 5 and subsequent block versions.

The U.S. has relied on its total undersea dominance for nearly three decades since the collapse of the Soviet Union, but that dominance is already fading, and is projected to flip upside down within the next decade. While perversely, due to the projected retirement of the rest of the aging Los Angeles-class SSNs, U.S. submarine forces will continue to fall over the same period, from 51 boats today to a projected 42 within a decade. The principle reason for the inability to build and operate the much larger SSN fleet of 66 subs that the Navy now says it needs is lack of funding. Some suggest that the answer is extending the service lives (SLEPing) of the Los Angeles-class boats, but that is not a practical solution, even in the short term, let alone the long term, since the maintenance burden for very old submarines is much higher than for new vessels. SLEPing old SSNs would only exacerbate the existing near-crisis of maintaining our these SSNs in operable condition.

Some say our small SSN fleet size is also due to a lack of “industrial capacity,” but the ability of the United States of America to ramp up its industrial capacity in times of severe military need is clearly proven in actual U.S. history throughout both World War Two, and during the long Cold War. If the funds to build all the subs that we need are actually made available, American industry will almost certainly respond, and ramp up accordingly, as proven time and time again. Make the construction dollars available on a predictable, multi-year contracting basis, and existing yards will open new lines, and/or new yards will be built, workers trained, and supply chains expanded.

In the 1960s through the mid-1970s there were six U.S. shipyards building SSNs and SSBNs, and in just 13 years of production the yards produced 39 boats, an average of three per year while at the same time producing 31 boats in multiple classes of Polaris and Poseidon SSBNs over just a five-year period. That came to on average of more than nine nuke submarines delivered per year at its peak in the mid-1960s.

As to the dollars needed for an expanded SSN fleet, the current full construction cost of a Virginia-class Block 5 SSN with Virginia Payload Module (VPM) stands at $3.2 billion in 2018 dollars. For comparison, the Sturgeon class-SSNs were built in the late 1960s for approx. $130 million each – in 2019 dollars that would be approximately $726 million – about a fourth of the cost of a Block 5 Virginia boat.

These behemoth Block 5 Virginia SSNs, at approximately 10,000 tons submerged, are more than twice the displacement of Cold War SSNs in the Skipjack-class, Permit-class, and the numerically large Sturgeon-class boats (4,300 tons submerged displacement). And to make matters more challenging, current naval plans for the next generation SSN, now dubbed “New SSN”³ suggest an even larger attack submarine, perhaps 12,000 tons and likely to cost $4 billion to $6 billion or more in 2018 dollars (and not entering the fleet for a decade or more) to build, and similarly expensive to operate. The Seawolf-class of SSNs were of approximately the same displacement, and the very high cost associated with building and operating the Seawolf SSNs encouraged limiting the class of boats to three hulls after the end of the Cold War.

The attack submarine Seawolf (SSN-21) conducts her first at-sea trial operation, following her early morning departure 3 July 1996, from the Naval Submarine Base, Groton, Conn. (General Dynamics photo)

Note that not only does raw displacement drive up the construction cost of a SSN (the rule of thumb is you pay for ships by the ton), but it also drives up the lifetime operating costs of the SSN. Manning a Block 5 Virginia-class SSN with its 42 vertical launch cells requires a crew of approximately 140 officers and sailors, as compared to the 99 officers and sailors of a Sturgeon-class SSN.

So why are the current class American SSNs so large?

The answer includes land attack – the new mission assigned to SSNs by the Navy in the aftermath of the end of the Cold War, with the virtually overnight disappearance of its main naval adversary, the Soviet Navy. By the early to mid 1990s the U.S. Navy was busy retiring aged-out Cold War boats by the dozens and was still building as replacements the last Los Angeles-class SSNs. These boats were larger than their predecessors, primarily to make them faster and capable of keeping up as escorts with CVN carrier battle groups and later on, carrier strike groups. Such high cruising speeds were not a requirement for anti-shipping warfare (both ASW and anti-surface ship) and ISR – the two primary missions of Cold War era SSNs.

Later on, the more advanced Virginia SSNs – as a smaller, cheaper, and slightly reduced capability version of the small class of Seawolf SSNs – came along by the mid-2000s, adding length, tonnage, and vertical launch tubes capable of putting up as many as 12 Tomahawk missiles (a similar vertical launch tube arrangement by then had also been added to some of the last Los Angeles-class boats). However, those post-Cold War Tomahawks on SSNs were not, like their Cold War predecessors, equipped to engage moving naval targets as long range anti-ship missiles, but instead were Tomahawk Land Attack Missiles (TLAM), capable only of engaging fixed land targets. The Navy was also busy deploying large numbers of TLAMs on large surface combatants, both Ticonderoga-class cruisers and Arleigh Burke-class destroyers, for the same deep strike land attack mission the Navy had taken on in the 1990s and beyond.

The latest Block 5 Virginias add a new “Virginia Payload Module” that adds yet another 84-foot section to the hull aft of the sail containing four more vertical launchers carrying as many as 28 additional TLAMs for land attack. The stated purpose of the VPM was to attempt to make up for the planned retirement of four SSGNs (converted Ohio-class SSBNs that were “denuclearized” per the START strategic nuclear arms reduction treaty). But of course that conversion of SSBN to SSGN was a “make work” solution for the resulting excess Ohio SSBNs above treaty limits, which has now begat a “make work” mission for SSNs. All of which bloats the boat itself and makes it much more expensive to build and operate.

Adopting the deep strike land attack mission was an understandable response to the drastic and virtually overnight elimination of a significant near peer naval threat in the 1990s. Thus the Navy and its supporters in Congress converted the navy virtually overnight to a deep strike land attack force in order to become more relevant to evolving national security interests, but at the expense of full-spectrum competence. Otherwise, naval leaders and proponents feared an even more drastic fleet reduction than the 50 percent cut that was actually made after the end of the Cold War.

This “keep the Navy relevant in the Post Cold War era” mindset was also aided and abetted by the Intermediate Range Nuclear Forces (INF) Treaty of 1987 limits on “land based” intermediate range cruise missiles (IRCM) that strangely did not apply to “surface launched” (i.e., naval platforms). (Both the U.S. and Russia have now withdrawn from this treaty, effective later this year.) In any event, INF encouraged both the Russian and U.S. navies to deploy large numbers of land attack cruise missiles on surface warships.

Clearly a lot has changed since the Post Cold War-era began. The U.S. military today is no longer simply tasked with combating low-capability insurgent forces in various and sundry developing nations often situated well inland, nor does the INF treaty apply as of this year either.

With the well-documented fast growing maritime threat posed especially by China (whose fleet of attack submarines is currently estimated to number over 70 vessels, and is expected to continue to grow at a rapid rate thereafter), as well as a resurgent Russian Navy, the world of naval warfare has now transformed from a low threat environment into a serious challenge to U.S. naval dominance. The U.S. Navy now has a clear and overriding mission – to deter and if necessary fight and win a naval war against capable near peer forces. Projecting sea power ashore continues as a U.S. Navy mission, but that mission is best and most cost-effectively performed by naval aircraft (both carrier-based and land-based), not by submarines. Given all of the above factors, then, and the fact that naval shipbuilding budgets are constrained, including demands to simultaneously recapitalize aging CVNs and Ohio-class SSBNs, the Navy must go back to the drawing boards.

Chairman of the Joint Chiefs of Staff Adm. Mike Mullen visits the Chinese People’s Liberation Army-Navy submarine Yuan at the Zhoushan Naval Base in China on July 13, 2011. (DoD photo by Mass Communication Specialist 1st Class Chad J. McNeeley/Released)

The Navy should consider designing a new SSN that is smaller and cheaper, and focused entirely on the anti-shipping and ISR roles – the historic roles of the SSN throughout the Cold War – with particular attention paid to building and operating many more new boats at a far faster build rate.

Size as measured in tons displacement, however, is not the only requirement and means of controlling cost – there is also the matter of modernization and capability. Obviously the technologies available today are far more advanced compared to those available in the 1960s and 1970s when the bulk of our Cold War era SSN fleet was built. For example, the later generations of U.S. submarines incorporated new propulsors – pump jets, rather than the older and noisier seven-bladed open screws on the Cold War era boats. Better sensors are also going into today’s boats, both sonars and “above the water” sensors, with photonic masts rather than periscopes, which allows more efficient interior hull design and better distribution of sensor data to various locations within the crew area. Better electronic warfare capabilities are also part of today’s fleet, and cyber warfare is increasingly a key area of focus in the 21^st century.

Better weapons are also available today, although advancements in deployed submarine-launched weaponry have clearly lagged behind both our adversaries and even of USN surface forces and naval air wings in recent years. Existing SSNs are still using the old Mk 48 ADCAP 21-inch torpedo first deployed in the mid-1970s, though significantly upgraded over the decades. But as of today the only submarine-launched anti-ship cruise missile available is still the old Harpoon Block 1C that was developed in the 1970s, and as of today only one of our existing SSNs has even re-integrated the Harpoon, as of last year. A new “Maritime Strike Tomahawk” refit kit is slated to become available in 2021 which will provide a new very long range ASCM capability to both submarines and surface warships with VLS. Perhaps other existing ASCMs such as the new Naval Strike Missile, now slated for deployment on LCS and FFGX, can and may also be integrated onto U.S. submarines, along with LRASM in the coming years.

Additionally, it should also be recognized that for purposes of anti-submarine warfare which was the primary role of the Cold War SSN, and which is now becoming a priority again, the Mk48 ADCAP torpedo is likely “overkill” for use against submerged submarines. The power of a 650 pound warhead on the Mk 48 certainly is helpful for attacking large surface ships, with the ability to literally break a ship in half when detonated under the keel. Submerged submarines, however, do not require such explosive power because of the effect of submergence sea pressure.

The lightweight ASW torpedoes such as the Mk 46 and Mk 54 (12.75 inches diameter by 8 feet 6 inches long, and weighing just 508 pounds vs. 21 inches, 19 feet, and 3,695 pounds respectively for a Mk 48) have for decades been in use by the US Navy and our NATO allies deployed on surface warships and ASW aircraft. The lightweight torpedoes have warheads with weights of slightly less than 100 pounds – demonstrably sufficient to sink a submerged submarine. Indeed, one of the most effective ASW weapons in WWII, the “hedgehog,” had a much smaller warhead of just 35 pounds of TORPEX. It was demonstrated that typically only one or two hedgehog detonations were needed to sink a submerged submarine.

An exercise Mark 54 Mod 0 torpedo is launched from the U.S. Navy Arleigh Burke-class guided-missile destroyer USS Roosevelt (DDG-80). (U.S. Navy Photo by Mass Communication Specialist 2nd Class Justin Wolpert)

Therefore, the Navy needs to give strong consideration to adapting existing lightweight ASW torpedoes to our next generation of SSNs. Doing so would facilitate the ASW capability of our SSNs while significantly increasing the sub’s capacity to store and deploy much smaller torpedoes. Not as a total replacement for the Mk 48, but rather, as a supplement to the Mk 48 to enable much larger total magazine depth without increasing the displacement of the submarine, to accommodate the ability to attack both surface ships and submarines. Instead of just four 21-inch torpedo tubes on a Virginia-class boat, a combination of 21 inch and 13 inch horizontal tubes optimized for a typical mission profile could work very well.

Finally, whatever combination of horizontal tubes and torpedoes is determined optimal, the weapons themselves need to continue to be updated to the latest technological capabilities as to sensors, self-contained computing (and artificial intelligence) as necessary to track and target submarines and defeat enemy countermeasures, and improved warheads. Hard kill anti-torpedo torpedoes as well as other torpedo countermeasures are also a prime area of development that needs to continue, despite a recent setback with the CAT weapon systems deployed on CVNs.

Nuclear propulsion technology is also advanced today over the old Cold War power plants. The latest generation of naval nuclear reactors as used on the new Ford class CVNs known as the A1B reactor are much more automated and simplified than the previous plants, allowing the highly trained and certified nuclear plant operator crew size to be cut in half as compared to the 1960s era reactors of the Nimitz class CVNs.⁴ Even more revolutionary nuclear power plant designs are going to be available to submarine designers in the next decade.

Similar technological opportunities abound to more heavily automate every work process throughout the next generation submarines, including artificial intelligence capabilities, and thus can significantly reduce overall crew manning requirements in a submarine. This has already been achieved on the latest surface combatants including the Ford CVNs and the Zumwalt DDGs, which respectively achieved overall manning reductions of 33 percent and 50 percent over their predecessor classes. A similar reduction in SSN crew size also ought to be achievable using the same design approaches and modern automation technology. Reductions in crew size also lead to reductions in hull volume.

Additional technology “insertions” are also available in other areas of submarine design that should be able to create significant impacts in both cost reduction as well as improving the capabilities of our next gen SSNs.

Conclusion

In consequence of all of the considerations described above, it is clear that NAVSEA needs to undertake a project to re-engineer the next generation of SSNs. Navy leadership has publicly stated its intent to reconfigure the surface fleet to significantly reduce the ratio of large surface combatants (LSCs) to small surface combatants (SSCs). The Navy now needs to similarly reconfigure the SSN fleet in favor of smaller boats optimized for sea control over long-range land attack. They must reject the bloated SSN(X) concept which is more of the same, but bigger and more expensive, and go for a new class of SSN that is far smaller and cheaper and thus affordable in much larger numbers than currently planned submarines.

Mr. Truitt is a veteran Cold War-era SSN sailor, qualified nuclear reactor operator, and civilian nuclear test engineer. He is also a degreed civil engineer, environmental scientist, and civil/environmental project manager with extensive experience at both naval and civilian nuclear facilities as well as military and civilian facilities development. His interest today as an author is in forward-looking military preparedness and improvements in both capacity and capability of U.S. naval forces.

Notes

1. USNI News, Ben Werner, March 27, 2019: “Indo-PACOM Commander Says Only Half of Sub Requests are Met”

2. USNI News, Megan Eckstein, April 8, 2019: “Navy Sees No Easy Answer to Balance Future Surface Fleet”.

3. USNI News, Megan Eckstein, May 13, 2019: “Virginia Block VI Subs Will Focus on Special Operations, Unmanned”

4. A1B Reactor; https://www.globalsecurity.org/military/systems/ship/systems/a1b.htm

Featured Image: YOKOSUKA, Japan (Sept. 3, 2010) The Virginia-class attack submarine USS Hawaii (SSN 776) transits Tokyo Bay on the way to Fleet Activities Yokosuka, marking the first time in the history of the U.S. 7th Fleet that a Virginia-class submarine visited the region. This is Hawaii’s first scheduled deployment to the western Pacific Ocean. (U.S. Navy photo by Lt. Lara Bollinger/Released)

Center for International Maritime Security

Tag Archives: submarine

Manning the Unmanned Systems of SSN(X)

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

Time to Re-Task, Downsize, and Re-Engineer the SSN, Part II

Time to Re-Task, Downsize, and Re-Engineer the SSN, Part 1

Fostering the Discussion on Securing the Seas.