Dr. Thompson is a professor at the University of Maryland, Baltimore and is a frequent contributor to THE SUBMARINE REVIEW.
As it has since the end of the Cold War, the Submarine Force faces a crisis. As nearly all readers of these pages know, the current one ship per year construction rate of Virginia-class SSN’s is insufficient to replace the Los Angeles vessels being retired. Unless action is taken, the inevitable result is the shrinkage of the Submarine Force to levels inadequate to meet national needs as stated in Joint Chiefs of Staff and Defense Science Board studies. While heroic efforts are ongoing to reduce the price of Virginias, it may be necessary to consider a different SSN to maintain adequate numbers of hulls.
In considering what type and how many submarines are needed, it is obviously necessary to consider the roles they play in the light of present and prospective future conflicts and missions. The roles submarines play are well known to Submarine Review readers: they include (roughly) antisubmarine warfare, anti surface warfare, ISR, special operations such as SEAL insertion, battle group escort, strategic deterrence, and inland strike. The argument has been made that submarines are very expensive as ISR (Intelligence, Surveil-lance, and Reconnaissance) platforms compared to aircraft, and that apart from a few Tomahawk strikes and some modest ISR they are poorly suited to the Global War on Terror in which we are currently engaged. Inasmuch as the war in Afghanistan and Iraq has evolved into a counterinsurgency struggle against small groups operating clandestinely using shoulder-fired weapons and improvised explosive devices, the publicly known contribution of SSN’s to the fight has now shrunk. While it is correct that an SSN is an expensive platform for the mission, the SSN offers important, indeed unique advantages in the ISR mission, some of which have been highlighted in the Submarine Review and elsewhere. First is its stealth, demonstrated during the Cold War in a higher threat environment than exists today in almost any theater of operation. Beyond self-protection, stealth avoids provoking or even alerting the quarry; many other JSR platforms such as most aircraft, satellites, and surface vessels are decidedly not stealthy.
Second is its endurance, where an SSN can stay on station for months with impunity, without support of any kind. Third is its payload and power budget, larger than any reconnaissance aircraft, particularly UA V’s. Aircraft have substantially less endurance, the best able to stay aloft for two days, with most able to spend less than twelve hours on station. While there are no publicly acknowledged operational stealthy reconnaissance aircraft (Global Star is not yet operational) several are in development. If detected, typical electronic reconnaissance aircraft such as RC-135 Rivet Joint or EP-3 are quite vulnerable to interception by SAMs or fighters. In circumstances where slaughter of innocents is a cornerstone of our current adversary’s strategy, we can expect little respect for conventions of war or territorial boundaries to protect ELINT manned aircraft (much less UAV’s). During the Cold War, several such aircraft were shot down (often with loss of the crew (A. Price, History of U.S. Electronic Warfare. Vol. I/, p. 166)), and the attack on the LIBERTY and capture of the PUEBLO are even better known. By comparison the SSN is clearly harder to detect, and hard to destroy even if detected with current systems; it certainly can defend itself against many threats if need be. It is important to add that while many second rate powers can afford (and possess) capable air defense systems, none have made the much greater investment in platforms and training to be credible at antisubmarine warfare. Since the end of the Cold War, airborne JSR has become a harder mission, while JSR from submarines has become easier. Even long-legged reconnaissance aircraft and UA V’s require some level of support, usually in theater; base traffic in third world countries may be under surveillance to cue potential targets. These desirable attributes have combined to make SSNs highly valued by commanders and national authorities alike as ISR platforms, as indicated by their increased tasking.
The improving acoustic performance of submarines of many nations provides a strong argument for producing more submarines As the radiated noise of current submarines of all nations continues to decline to levels where ambient noise becomes increasingly significant by comparison, we will enter a regime where passive detection becomes more difficult and maximum detection ranges shrink. Particularly in noisy or oceano graphically complex waters, enemy submarines may not be detectable at useful ranges even though our ships have an acoustic advantage in radiated noise. This has the effect of enlarging the ocean and making all antisubmarine platforms (including our SSN’s) less effective. We’re listening for our opponent at a cocktail party, instead of in a library. As a result, the effectiveness of our SSN’s in some ASW scenarios would be reduced, even against less capable opposing submarines, such as diesel-electrics. For instance, neutralizing a Chinese SS threat to a carrier battle group in the vicinity of Taiwan would be more difficult if maximum detection ranges were halved, even if we can be confident of detecting the opponent on battery first. Operations research techniques dating to World War II enable one to calculate the likelihood of detecting the target if the detection range is reduced (expressed mathematically as a coverage factor WLA (see U.S. Naval Institute, Naval Operations Analysis. 2nd Ed., 1977). Thus in such scenarios there is no substitute for more sensors and probably more platforms; for ASW, clearly the platform of choice is the SSN.
While the case can be made (to those who are listening) for an adequate SSN force, it remains a fact that state of the art submarines remain very expensive, with the current Virginia class coming in at $2.1 billion apiece (R. O’Rourke, Submarine Review July 2006, p.69). It is likely that the Virginias are the cheapest ships that can be built with their capabilities, but inasmuch as one costs a significant fraction of the annual shipbuilding budget, it is perhaps unsurprising that the Government has been so far unwilling to increase production to two per year despite the significant savings that would be realized per ship. Admiral Holland points out that we have not succeeded in making this case to the folks outside the submarine community, but letting the Submarine Force shrink is an easy way politically to afford the other things the DoD and Navy want, inasmuch as the shipbuilding budget is perceived as being a zero sum game and quite regardless of the strategic consequences.
VIRGINIA and her sisters are very flexible and capable ships, being able to carry out missions in strike warfare and special operations as well as ISR, anti surface and antisubmarine warfare. While smaller than the Seawolf class, they are comparably sized to the Los Angeles class. Estimates (Polmar, Ships and Aircraft of The U.S. Fleet, 18’~ Edition, (2005)) credit VIRGINIA with a speed in excess of 25 knots from her 25,000 horsepower S9G reactor plant, somewhat less than the S6G of Los Angeles and much less than SEAWOLF. LOS ANGELES was designed with high submerged speed in mind (Friedman, U.S. Submarines Since 1945, An Illustrated Design History (p. 163, 1994), in part to enable it to keep pace with carrier battle groups.
There are economic and acoustic advantages to building larger submarines: some of these have been discussed by Holland. It may be that some silencing features necessary to go fast and stay quiet are not only costly, but difficult to incorporate in a small hull: it may not be possible to go faster than 20 knots and still be quiet enough to hear in a hull smaller than Virginia’s. As in other ship construction, once one has spent the bulk of the money on developing and procuring the sonar, reactor plant, and combat system, there is little money to be saved by building a smaller ship around it that will be less capable. Certainly many different size/capability options were considered in the design of VIRGINIA (Friedman, p. 213). Also, there are the large, essentially fixed overhead costs of the yards themselves, that are also a major cost driver.
Yet for many of the missions the US Navy requires of submarines, a smaller, somewhat less capable but significantly less expensive ship might suffice. A non-nuclear submarine cannot adequately perform nearly all of the missions we require and will not be considered further; readers are referred to Captain Patton’s recent article (July 2006 Submarine Review) for a thorough discussion of the reasons why air independent propulsion (AIP) is not a viable substitute for nuclear propulsion. However, a small (perhaps TULLIBEE-sized) SSN might be worth considering, if we no longer expect it to do 25 -30 knots but 20 +instead. In particular, it may be possible to get VIRGINIA-level quieting in a < 5,000 ton hull, and still do most of what we deploy subs to do, if the reactor plant is significantly less powerful than VIRGINIA's S9G. TULLIBEE's S2C plant only produced a reputed 2500 shp with her turbo electric drive, giving her a reported top speed of 16 knots; clearly something larger would be necessary. It may be difficult to make a reactor in this size range that is quiet (perhaps incorporating natural circulation cooling) and still thermo dynamically efficient. An SSN with only 2o+ knot speed would be much less attractive for the CV battle group escort role, but we note that the vast majority of U.S. SSN's will have adequate speed for this mission into the foreseeable future. Recently(M. Henry, Brief lesson in Submarine Design,” Submarine Review, January 2006, p. 31) some of the tradeoffs necessary in submarine design were lucidly described, and we do not propose to design a new ship herein, but to consider whether a significantly cheaper albeit smaller ship is feasible.
Particularly for ISR and some special operations missions, smaller size would offer important advantages. For maneuvering in confined waters, or where tides and currents are significant, a smaller hull is desirable. Some areas of current (or future) interest, such as the west coast of Korea, have large (10 meter) tides and fast (8kt) currents, where an SSN (much less an SSGN) might find herself aground. Notwithstanding all the virtues of the Ohio-class SSGNs for special operations, maneuvering them close inshore will remain a challenge due to their large displacement and length overall. The use of thrusters at the bow can address this issue, but at some cost in stealth, and due to their modest power their effectiveness is limited as well. The ability to get close inshore to minimize transit time to and from the submarine to shore can also be important for special operations where hours of darkness, tides, or phase of the moon may be tactical factors for the success of the mission. Similarly, most current US SSN’s are relatively tall, in that the distance from the keel to the top of the sail is 50 feet or more versus about 40 feet for TULLIBEE. While maneuvering submerged in shallow water will always be exciting, a less tall SSN would have a greater margin for error than our current SSN’s. For Arctic missions passing through the Bering Strait and shallow Chukchi Sea a smaller height overall can make the difference in the presence of deep ice keels (see W. M. Leary, Waldo Lyon and the Development of the Arctic Submarine, Texas A and M University press, 1999). In a world where the acoustic signature of submarines continues to shrink, active sonar becomes increasingly attractive to many navies; with other things being equal, a smaller submarine is less detectable.
Magazine capacity was an important driver in the design of SEA WOLF, because she anticipated operating in a target-rich environment (Soviet SSBN “bastions”) where resupply would be difficult. The incorporation of the VLS tubes on the Improved LOS ANGELES (and VIRGINIA) classes has greatly improved their utility as strike platforms. Yet for most ISR, ASW, and special operations missions there seems only modest value to carrying many weapons: for JSR and special ops one does not anticipate shooting at all, except as a last resort. Most ASW scenarios today are unlikely to include many targets: SEA WOLF by herself carries enough torpedoes to wipe out the entire Submarine Forces of almost any prospective opponent, and even a LOS ANGELES is unlikely to encounter enough targets at which to shoot twenty torpedoes. For anti surface warfare one also does not anticipate the need for magazine capacity that would have been desirable back in World War II, largely because aircraft and their weapons have become so much more capable that in most scenarios enemy surface ships (transports or warships) are essentially en prix. These are some of the reasons the Virginias were reportedly built with reconfigurable torpedo rooms. Moreover, there seems little likelihood that the factors listed above in favor of high magazine capacity (apart from strike warfare) will reemerge. The point is that for many missions a magazine capacity more like TULLIBEE’s (reputedly twelve weapons) would suffice, and the submarine might be made correspondingly small.
Are there other advantages to a smaller ship? Are there other opportunities for cost savings? TULLIBEE had a complement less than half that of a LOS ANGELES. While the savings in salary might add up to a significant dollar figure over the life of the ship, the savings in weight, size, and habitability features in having to support a smaller crew might be nearly as significant. It is not at all clear that a modem ship could safely operate with as small a crew as TULLIBEE, or be as survivable, but reduced manning may be worth exploration. Modem sonar is strongly computation-dependent, and certainly the trend (up through ARCI) has been to incorporate as much processing power as possible into the combat system, and to integrate its functions as fully as possible. BSY-1 was large, both in terms of weight (32 tons) and volume (117 cabinets), as well as power ( 142 kW) and cooling consumption. Have modem processors gotten to the stage where they have as much computing power as needed? Put another way, have modern computers gotten to the point where the processors and displays at least can significantly shrink in terms of size, power, and cooling consumption? Could you now build a combat system with 90% of the capability of BSY-2 for 1 /3 the cost per ship without spending billions developing it?
We have tried to consider some of the issues involved in the development of a smaller, less expensive, but ultimately less capable submarine. This smacks of Admiral Zumwalt’s high-low approach to escort design which led to the Perry-class frigates, and which was not well thought of in many quarters. Yet the alternative would appear to be an inadequate number of submarines to carry out even current missions for the foreseeable future, much less fight a major conflict. In view of the long lead time needed for producing some submarine components and the reduced construction and overhaul capacity and labor force for nuclear submarines compared to the 1960’s, quickly ramping up production significantly in the face of a growing threat would appear problematic. At that point the question may not be can we afford two SSNs per year, but are we able to build four (or six) per year at all.