Defense analysts periodically propose a mix of nuclear and conventionally powered submarines to increase U.S. undersea force structure. They argue that conventional submarines (SSKs) are so affordable the U.S. could acquire multiple boats for the price of a single nuclear-powered attack submarine (SSN). In an era of declining fleets and looming budget cuts, that sounds appealing. However, despite increasing capability, conventional submarines still lack the payload, endurance, mobility and affordability necessary to meet U.S. needs, even when forward-based and equipped with air-independent propulsion (AIP).
The modern SSK is a formidable weapon, improved significantly over its World War II predecessors. Mechanically, it still depends on simple and forgiving technologies such as diesel engines, electric motors and large storage batteries. Tactically, it carries advanced sensors, combat systems and payloads — it can deliver a powerful punch. The SSK is among the stealthiest of modern combatants, and designers continue to address signatures associated with snorkeling, when it is most detectable. In recent years, new equipment mounting techniques and better exhaust management have reduced acoustic and infrared snorkel signatures. Operating fully submerged on the battery, the SSK is very difficult to detect and challenges even the most capable anti-submarine warfare (ASW) force.
Despite its attributes, the SSK has considerable shortcomings, many of which relate to size. These small ships have limited stores, battery, fuel, payload and crew capacity, which in turn limit their endurance, agility, persistence and combat capability. The modern SSK ranges in size from the 1,500-ton Swedish Gotland class to the 3,350-ton Australian Collins class. Some countries are building even smaller submarines, including the French Andrasta-class coastal SSK (855 tons) and the North Korean Yono-class (130 tons) midget submarine — the same type believed to have torpedoed the South Korean corvette Cheonan in March 2010.
Automation has helped reduce SSK crew requirements. Unmanned engineering spaces are common, and propulsion systems are often operated remotely from the control room. However, small crew capacity often places watch teams in extended port and starboard (two-section) rotations — a practice that can quickly reduce a crew’s effectiveness on patrol. To offset these size-related constraints, several countries are considering larger boats. For example, French shipbuilder DCNS plans to offer a larger version of its 1,800-ton Scorpene SSK to India, which wants the added volume to increase endurance and payload capacity. Australia, whose Collins-class ships are already some of the world’s largest conventional submarines, is planning an even larger replacement. It is estimated this follow-on boat will displace in excess of 4,000 tons to meet the endurance, payload and crew requirements outlined in Australia’s 2009 Defence White Paper. To put this in perspective, the U.S. Sturgeon-class SSN — a mainstay of the Cold War — displaced approximately 4,700 tons submerged. As countries incorporate technologies to increase SSK quieting, endurance and other combat capabilities, they are moving toward designs with larger displacements.
Notwithstanding this trend, many SSK advocates highlight their small size as a significant advantage when operating in shallow, littoral areas — both in terms of the depth of water they can operate in and their maneuverability. However, this advantage is overstated and supposes a capability gap that does not exist. Specifically, SSK advocates imply there are areas where the U.S. cannot operate a SSN because its navigation draft is too large or it lacks maneuverability. That is not true. The Virginia-class SSN is about 15 feet taller (measured from the keel to top of sail) than a typical SSK. That difference is not significant in the waters U.S. submarines patrol to safeguard our national interests. While an SSN may incur slightly more risk than a SSK in some very shallow areas due to operating closer to the surface or bottom, the SSN can offset that risk by repositioning or evading at higher speeds for an indefinite period. Finally, it’s worth noting the Virginia-class SSN was designed to operate in shallow littoral areas and has a sophisticated depth-keeping and maneuvering system that can match or outperform the most capable SSK.
In terms of maneuverability, SSK advocates paint a false picture of undersea navigation. Submarines do not typically operate submerged in areas that require them to turn on a dime or maneuver through narrow undersea canyons. Tom Clancy’s thriller “The Hunt for Red October” contained a scene in which a Soviet ballistic-missile submarine maneuvered deftly between “Thor’s Twins.” That was entertaining, but it was not reality.
Stealth is the essence of submarine warfare, and conventional submarines are acoustically stealthy, especially when operating submerged on the battery. However, they need to snorkel periodically to recharge their batteries, making them more vulnerable to ship and airborne ASW forces that are increasingly adept at detecting a submarine’s masts and antennas. Scheduling this evolution to occur at night helps avoid visual detection, but does nothing to avoid radar, which is a more common means of finding snorkeling submarines. If equipped with AIP, an SSK can operate submerged for up to several weeks, but only at slow speeds. However, AIP systems require fuel and oxidizers they cannot recharge at sea. Once they are used, the SSK must return to port to regain its AIP capability. That will likely cause skippers to hold their AIP capability in reserve for dire tactical situations, or where mission accomplishment demands it. Under normal situations, the SSK has to deal with all the vulnerabilities and limitations associated with snorkeling: slow speed, acoustic transients, elevated noise levels, increased infrared signatures and long-term mast exposure.
SPEED AND ENDURANCE
SSK advocates acknowledge the SSN can operate submerged at high speed for extended periods, which is a significant advantage. They also acknowledge the value of speed in evading threats and repositioning quickly to collect intelligence or engage a target. However, they routinely discount that same speed advantage while transiting to and from mission areas. They assert that forward-basing a U.S. SSK fleet would eliminate the SSN speed advantage. That argument is problematic from several standpoints.
First, if forward-basing more submarines were simple, the U.S. would already have more than three SSNs stationed in Guam. However, forward-basing entails considerable costs, including pier infrastructure, maintenance facilities, housing and a range of personnel support requirements. Together, these additions result in a large footprint — something indigenous peoples appear less willing to tolerate and something adversaries can hold at risk with a growing arsenal of ballistic missiles.
Even if one ignores the costs and risks associated with expanding overseas facilities, the fact remains that long transits are still required. It is approximately 1,500 miles from Guam to Taiwan. An SSN can easily cover that distance in a few days — even less in a crisis. The SSK, by contrast, needs seven to 10 days, which is highly weather dependent. Unlike their World War II predecessors, today’s SSKs cannot transit any faster on the surface than they can while snorkeling. They can reach speeds up to 20 knots submerged; however, they can do that only for a few hours until the batteries are exhausted. Of course, while snorkeling at higher speed, the SSK is vulnerable to detection not only by the methods discussed earlier, but also because of the larger wake left by its snorkel mast and periscope. Moreover, a round-trip transit of 14 to 20 days represents one-third of the SSK’s overall endurance — it has much less on-station time than an SSN. That would require more ships to meet U.S. deployment needs.
SSK advocates also discount the need to reposition deployed submarines within or between theaters during a given patrol, often at great distances. Some claim that operations in shallow littoral waters prevent even the SSN from rapidly repositioning. Current submarine operating area bathymetry does not support that claim, nor is it representative of how combatant commanders are employing submarines. Even when operating in very shallow water, an SSN can increase its transit speed as water depth increases, whereas the SSK can never reposition at high, sustained speeds regardless of available water depth. If a mission requires a submarine to reposition to another theater, an SSK could spend more than half its patrol endurance in transit. Additionally, all ships eventually require periodic depot-level maintenance, which requires returning to Pearl Harbor, Hawaii, or the continental U.S. Over the life of a forward-based SSK, this additional lost transit time would further degrade its operational availability. Considering speed alone, one can reasonably argue it would take two or more SSKs to provide the same on-station time a single SSN can provide.
Adding SSKs to the U.S. submarine force would provide realistic and more-effective training targets for our ASW forces. SSK advocates are correct in noting this would be a convenient benefit. However, it is unnecessary. U.S. security partners, especially South American navies, provide conventional submarines in support of fleet readiness events. In 2001, U.S. Fleet Forces Command formalized a partnership called the Diesel-Electric Submarine Initiative (DESI) program. The Commander Submarine Force’s executes DESI and provides the U.S. Navy with an elevated level of ASW training against the growing SSK threat.
The most prevalent and, at first glance, most compelling argument for adding SSKs to the Navy is their low acquisition cost. SSK advocates recommend buying them from a foreign builder as the cheapest option, but also consider U.S.-built SSKs as more cost-effective than the nuclear submarines it currently builds. Unfortunately, in the context of the SSK-versus-SSN debate, price itself is obfuscation. SSK supporters often cite brochure prices that do not include sensor and combat-system packages. Additionally, they fail to recognize that these foreign-built submarines lack U.S. Submarine Safety Certification (SUBSAFE) requirements. The SUBSAFE program was born out of the Thresher disaster in 1963, when the nuclear-powered attack sub was lost with all hands due to design and maintenance deficiencies. The SUBSAFE program ensures proper design and materials are used in systems subjected to sea pressure or required for emergency recovery. In addition, it ensures only trained and certified personnel install or repair these systems, and that builders, maintainers and crews maintain auditable certifications for each critical component and system joint. These material, procedural and administrative requirements are vital to ensuring the safe operation of our submarines, and they have real costs associated with them. The lack of similar or as robust programs among SSK manufactures makes the price of their ships — at least superficially — more appealing.
Of all the modern SSK producers, the Australian submarine program is probably closest to the U.S. SUBSAFE program and standards. Additionally, in some respects its deployment transit lengths to critical theaters and submarine combat requirements are also most comparable. Interestingly, early projections for its follow-on SSK class calls for a force of 12 boats at a cost of $36 billion. That equates to approximately $3 billion per boat (including nonrecurring costs) and is very different from the $500 million per boat that SSK advocates often cite.
Studies assessing the viability and utility of adding SSKs to the Navy have examined a number of attributes. Two of the more significant metrics compared were life-cycle costs and equivalent effectiveness. While SSK advocates often focus on the life-cycle cost of a single SSK versus one SSN, a more useful comparison considers life-cycle costs for the number of platforms that provide equal on-station capability. This is the variable of significance to combatant commanders. Based largely on the factors discussed above, studies indicated it takes 2.2 to six SSKs to obtain the equivalent effectiveness of a single SSN. Even after accounting for the lower SSK cost, an SSK fleet with equal on-station capability as an SSN fleet would have life-cycle costs of 1.3 to 3.5 times that of an SSN fleet. The SSK is simply not an affordable alternative.
These platform equivalency comparisons highlight the inadequacy of comparing the acquisition cost of a single SSK to an SSN because there are other factors to consider as well. Adding a mix of SSKs to the U.S. submarine force will increase the associated logistics, maintenance and modernization, and training costs due to having to maintain a second line of parts, repair capabilities and trainers. Some commonality of systems may be possible. However, numerous systems and functions are unique to either submarine class. Additionally, since the U.S. would most likely produce SSKs indigenously, there would be significant added costs to outfit the shipyards to build the conventional submarines. Simultaneously, the costs to build the nuclear submarines would go up due to the reduction in economies of scale associated with building two Virginia-class attack submarines per year.
Despite these compelling equivalency comparisons, some SSK advocates continue to focus on the claim that for the same procurement dollars the U.S. could buy more submarines if they included conventional platforms. They emphasize that quantity has a quality and capability all its own. While former Defense Secretary Robert Gates and others have used this argument to discuss programs in general, they were not advocating that capabilities associated with quantity alone should trump all others. It is but one factor to consider. Unfortunately, for those advocating adding SSKs to the U.S. inventory, a comparison of almost every other capability consideration and metric shows that a force of only SSNs is the most cost-effective way to provide our nation the undersea capabilities and capacity it needs.
One thing SSK and SSN advocates can agree on is the need for submarines. That need is growing and stems from the proliferation of threats to nonstealthy surface ships and aircraft — the mainstays of Navy power projection. Those platforms, along with forward bases, are becoming increasingly vulnerable to precision-guided weapons ranging from man-portable missiles and guided mortars to the most sophisticated surface-to-air missiles and anti-ship ballistic-missile threats. The submarine’s immunity to these threats and the nonprovocative nature of its presence provides commanders with much-needed intelligence preparation of the battle space, as well as strike, anti-submarine warfare, anti-surface warfare, special operations support and other missions.
U.S. adherence to an all-SSN fleet stems largely from its defense philosophy, which is to project power overseas and keep conflict far from the continental U.S. Even if forward deployed to Guam, the SSK is a poor investment as a power-projection platform. It lacks the agility, endurance and payload capacity for that mission. As potential competitors build more nuclear-powered submarines, a shift toward a mixed fleet would increase the risk of the U.S. losing undersea dominance. Repeated defense reviews, including those by the United Kingdom, concluded that nuclear-powered submarines were in the best interest of their national defense needs. Emerging powers such as India and Brazil seem to agree with those conclusions, since they have both embarked on their own nuclear-powered submarine programs.
Technological advances such as AIP continue to improve SSK capabilities and our country’s security needs continue to change. Consequently, the Navy should periodically revisit this issue and determine if a mix of nuclear and conventionally powered submarines is appropriate. If some future AIP technology can provide the same power, endurance, reliability and safety as naval nuclear reactors provide today, that technology would be a game-changer and worthy of consideration. Short of that, the SSN will remain an indispensable element of the Navy’s fighting team. The SSK is a useful and capable platform for many countries seeking to defend their littorals. However, it is still not the right answer for the unique power projection needs of the United States. AFJ