In littoral warfare, the Navy’s present attack submarines may not always be able to accomplish the mission. A less sophisticated, more agile boat with an alternative propulsion system—the X-1 used hydrogen peroxide for submerged operation of her diesel—might be better suited.
With “Forward . . . From the Sea,” the U.S. Navy sets forth a vision of how it will conduct operations in the post-Cold War era. The emphasis is on littoral warfare, where naval forces will project high-intensity combat power ashore against regional threats.
The new vision provides a strategic orientation, but it does not provide a recipe to determine the doctrine or force structure needed to implement it. Does the current doctrine governing attack submarine employment need reformulation? What kind of attack submarine does the Navy need to conduct littoral warfare?
Missions
One of the most important missions attack boats should be able to accomplish is to sweep the littoral objective area clear of enemy submarines. This sanitization should begin before hostilities: our submarines should be tracking enemy submarines during the transition to war. This would facilitate the immediate destruction, when hostilities begin, of the “marked” enemy boats. To accomplish this, U.S. submarines must be able to go everywhere enemy submarines travel, even into shallow water.
This mission often can be accomplished by our present nuclear attack submarines (SSNs), but not always. For example, a savvy enemy captain—especially if he knew roughly when hostilities were going to begin—could shake the U.S. submarine trailing him by entering water that only his smaller boat could cross. Then, once hostilities started, the stage would be set for an underwater dogfight. In such a shallow-water situation, the larger—perhaps less quiet—SSN probably would be at a disadvantage.1 This is especially likely if the enemy is operating in more familiar seas.
U.S. submarines also could dispense mines, with the aim of killing enemy boats or blockading them in port, or could help defeat enemy mines. The problem here is that the Navy needs to be able to complete littoral mine clearance in the face of a capable enemy—for example, one who possesses Exocet antiship missiles, antiair systems such as SA-10s, and a competent air force—and U.S. mine countermeasures assets would be extremely vulnerable in such an environment. It is problematic whether they actually would attempt to locate or clear mines.
A submarine, however, probably could locate and might even remove mines using unmanned undersea vehicles and explosive ordnance disposal personnel. In fact, submarines may be the best platform to locate and destroy mines until threatening enemy systems are removed. This concept is not new: our submarines mapped Japanese mine fields during World War II.2 Again, submarines assigned this mission must be able to operate in shallow water, possibly in depths less than 50 feet. Mine countermeasures forces worked shallower depths during Desert Storm.3
Submarines also should be able to attack targets ashore and to threaten enemy platforms such as patrol boats. To do this effectively, a submarine must be prepared and able to operate close to the enemy coastline, freely attacking targets, both at night and during the day, even if doing so would give away its position.
Another mission is the support of special forces. This could consist of dropping off teams and providing them protection and on-call fire support. This requires boats that can operate in shallow water, close to the teams they support, to provide immediate assistance. Submarines also could survey the littoral area comprehensively and continuously using diverse sensors. Data gathered by a covert submarine can prove to be more useful than data obtained by overt platforms.
Employment Doctrine & Capabilities
These missions are premised on an aggressive employment doctrine, which envisions that U.S. submarines will get right in the face of the enemy and dare him to engage. The submarine’s stealth, while still an important asset, no longer would be the ultimate tactical consideration. In fact, this approach works best when the enemy has a rough idea of the submarine’s location, because he may then conclude incorrectly that he has the advantage. Thus, while U.S. submarines still may lurk passively, waiting for targets of opportunity, under the paradigms advocated here they normally will seek out the enemy to harass or attack him. When the enemy responds, he will find an adversary ready and eager to brawl. There is precedent for this aggressive posture:
In April [1944] the U.S. Pacific submarines were ordered to concentrate on Japanese destroyers. Hair-raising tactics were adopted to this end, such as the coldblooded “down the throat” shot—deliberately courting a ramming attack on the surface, and torpedoing the destroyer as it came in for the kill. No less demanding in skill was the “up the kilt” shot: surfacing in the wake of a hunting destroyer and torpedoing it up the stern. The campaign against the Japanese destroyers was a resounding success: 39 of them had been sunk by submarines by the end of the war.4
Such an aggressive posture is once again appropriate. The United States almost certainly will bring overwhelming force to the littoral objective area. This means that our attack boats, functioning as part of an integrated joint force, will have mission support. Consequently, enemy forces will have to contend not only with our potent submarines but also with U.S. air power. Tomahawk- firing surface ships, and missile- and gun-toting helicopters.
Another factor that makes this posture feasible is information technology. The United States will have the sensor and electronic architecture to detect changes in the operational and tactical situation quickly and to transmit these data to its forces instantly. On-scene commanders will be able to exploit opportunities and preempt enemy salients. This will permit the almost immediate destruction of platforms that threaten U.S. submarines.
The fighting posture advocated also can be adopted because a submarine can have capabilities that make it a vastly more useful and survivable weapon system that can contribute decisively to littoral warfare. For example, submarines could release and control unmanned undersea vehicles (UUVs) to locate mines. UUVs could use side-scanning sonars, laser line-scanners, or perhaps technologies resident in the AN/SLQ-48 mine neutralization system now found on countermeasures ships. Mines then could be destroyed quickly, maybe by a system such as the GEC-Marconi Archerfish—a self-propelled mine disposal weapon controlled via fiber optic cable.5 Submarines may be too slow for high-intensity mine clearance, but their ability to covertly locate and map mine fields before hostilities could be instrumental to success.
To attack enemy targets in the littorals and ashore, the stand-off land attack missile (SLAM) now in inventory—Tomahawks are too expensive for many targets—should be adapted for submarine use. A version of SLAM controllable via fiber optic cable would be useful, allowing the weapon to be targeted selectively in the presence of background shipping. As an alternative, guidance commands might be transmitted from a remotely piloted vehicle, with the submarine providing the weapon. A version of SLAM that uses the global positioning system also should be available for use against fixed targets. Another weapon candidate, which the Navy has begun testing for naval use, is the Army tactical missile system.6
Because a water exit point creates a “flaming datum,” missiles ideally would not be fired directly from the submarine but from a weapon module previously dropped out of its hull. The modules, filled with a variety of weapons and, when needed, deploying a floating sensor pod to aid weapon designation, could be operated from the submarine via a fiber optic tether. If necessary, the submarine could break the umbilical, knowing it could be reestablished.
U.S. submarines, because they are vulnerable to detection in shallow water, also must be able to deal with enemy aircraft. With the synergy of artificial intelligence and cheap microprocessors, weapons that are effective against maritime patrol aircraft and helicopters should be a certainty. On balance, aircraft probably would find that their antisubmarine weapons performed poorly in shallow water, while the submarine’s antiair weapons worked much better.
U.S. submarines also should have decoys to help protect them in shallow-water encounters with the enemy. Such a decoy might behave like a maneuvering submarine. Or it could make it harder to locate the submarine by confusing the environment around it, for example, by detonating explosives, dispensing irritating aerosols, or spewing fluids that degrade or incapacitate a ship’s propulsion plant or sonar.
The Littoral Warfare Submarine
What type of submarines does the Navy need for littoral warfare? Los Angeles (SSN-688)- and Seawolf (SSN-21)-class boats are needed to deal with the submarines Russia continues to field, but these classes are not well suited for littoral warfare. They are too expensive and too sophisticated to hazard in risky littoral missions unless vital national interests are at stake. A U.S. SSN sunk where an enemy was able to recover its technology intact would be an incalculable loss.
The second reason U.S. attack submarines are less than optimal in the littorals is their size. The Navy needs a class of boats smaller than the 6,900-ton Los Angeles or 9,000-ton Seawolf. Smaller boats could operate with more agility in shallow water.7 For example, a 360-foot long Los Angeles-class boat, traveling rapidly at a keel depth of 90 feet in 110 feet of water, encountering an underwater obstacle requiring an ascent of 30 feet might face the choice between burying its stern in the bottom, broaching, or both. A smaller boat could have been at a keel depth of 50 feet and avoided the entire excursion.
The draft of a surfaced Los Angeles-class boat is 32 feet, and that of a Seawolf is 35, with both having an overall height greater than 50 feet. These behemoth boats need more water just to submerge than a Nimitz-class carrier draws. Their drafts are so deep they cannot be flexibly employed in places such as the Persian Gulf, and vast areas in the Yellow, East, and South China seas. The same will be true for the proposed 6,000-plus ton new attack submarine (NSSN).
Another drawback of large boats is that they are more detectable visually; larger boats cause more disruption of their surroundings. For nuclear submarines, this is partly because they must suck in considerable water to cool their plants. When operating over silty bottoms, this could be fatal. Larger boats also displace more water, which adds to their propensity to disrupt their surroundings. In warm water, where bioluminescence often is present in the shallows, this is a serious concern.
Large boats, because of their larger propulsion plants, also have more pronounced heat signatures. This signature, difficult to detect if a boat is in the depths, becomes a concern in shallow water. Infrared equipment could detect the thermal scarring created by a plant’s discharge. This is particularly true if the submarine loiters: a status that may often be tactically expedient in the littorals. Another factor is magnetic signatures. Smaller boats disrupt less of the earth’s magnetic field, making them harder to detect with magnetic anomaly detectors. A large submarine may escape detection in the depths, but this is more difficult in shallow water, even with sophisticated degaussing.
When operating in the littorals, smaller submarines, including nonnuclear submarines, have tangible advantages. In fact, nuclear propulsion is no longer the undisputed best for deep-water operations, as it was in Cold War. Numerous technologies could provide propulsion options. Even diesel boat technology probably could deliver most of what the Navy needs, i.e., a relatively inexpensive platform for aggressive operations in the littorals.
The Germans during World War II blazed the way in experimental propulsion systems. “The most revolutionary prototype was the Type XVIII, with its Walter turbine powered by ‘Perhydrol’: peroxide based, burned with oil, independent of outside ventilation and capable of delivering bursts of speed up to 25 knots.”8 The United States also experimented in the 1950s with advanced conventional systems, including some that used hydrogen peroxide.9 Hydrogen peroxide systems proved dangerous, however. There are better options now.
For low-speed propulsion, some form of a Stirling system may work. The Swedish, German, and Australian navies are pursuing this alternative in which “heat is supplied externally and continuously to a working gas in a closed system.”10 These engines are very quiet because they do not require periodic detonations of fuel nor is there valve clatter. Swedish testing of this engine met or exceeded all requirements. “Previously the submarine’s capability to operate submerged without recharging batteries was counted in days while after the installation of the Stirling plant it was extended to weeks.”11 The technology has matured enough that the German Submarine Consortium advertises that its air-independent systems can extend conventional submerged endurance “at least by a factor of five.”12 Another promising air-independent system is seen in the Italian Maritalia designs. The 136-ton version of such a submarine had a submerged endurance of 14 days with submerged burst and transit speeds of 18 and 8 knots, respectively.13
Power-storage technology also is in flux. Considerable power might be provided by a counterrotating composite flywheel arrangement that potentially can store more energy than batteries in the same amount of space.14 Aluminum-oxygen fuel cells also are promising, with such a cell providing about “ten times the energy density of lead-acid batteries and three times that of silver-zinc cells.”15 Battery technology also is improving. Australia is producing 2,700-ton Collins-class boats suitable for worldwide deployment. Their batteries give them a submerged endurance of 120 hours at a continuous speed of four knots. They may fit Stirling engines in the boats to obtain more.16
But littoral missions do not require sustained, high-speed submerged operations. And speed must be used conservatively. A submarine moving at shallow depths can displace enough water to leave a surface wake and other disturbances that are detectable by sight, sonar, or radar. Modern weapons also obviate much of the need for speed. A submarine no longer needs to scramble to get in front of a target to attack it. If a submarine does need speed, say a burst to get away from an enemy’s weapon, batteries are capable of providing it.
A submarine that will operate in the littoral does not need a great deal of range. Boats can deploy to the littoral objective area on the surface. But range is not a problem. For example, Foxtrots can go 11,000 miles at eight knots.17 These are boats with old technology.
Most will argue that what is important is submerged endurance, but how much endurance is needed in littoral warfare? Five days of submerged endurance at four knots is enough for most missions. More endurance certainly is attainable simply by loitering, particularly if a submarine can rely on an air-independent engine for power to make air and water. But if more on-station time is required, another boat could replace the one on station. After all, we are not considering anything nearly as difficult as relieving an SSN covertly marking another. Indeed, relief is desirable as the intensity of high-threat, 24-hour-a-day, littoral warfare exhausts a crew. Also, as expeditionary warfare assumes that U.S. forces will control the sea and air, even a diesel boat should be able to recharge batteries. The indiscretion of snorkeling could be lessened if boats were fitted with a stealth snorkel, as some German diesel boats were in World War II.18
There could be many pluses to deploying conventional submarines. They would be invaluable for tactical development and training. They also are inexpensive to operate. For example, the British defense ministry revealed that it costs $16 million a year to operate a Trafalgar-class SSN and $3 million for an Upholder-class SSK.19 In addition, conventional boats do not pose the environmental issues and costs. Nuclear boats are forbidden to enter some foreign ports because of the specter of reactor accidents.
Even more important, because of less rigorous construction requirements, more revolutionary submarine designs are possible. Nuclear propulsion plant safety concerns and quietness no longer need determine the fundamental design of a submarine. Also, shallow-water boats do not need to be constructed to the same standards as deep-diving vessels. The hull, weapon-launching systems, and auxiliaries do not have to overcome as much pressure. These differences would allow less expensive construction. Hulls and other main structures might even be constructed of fiber reinforced polymer composites, which would be stealthy yet strong. Conceivably, composite hulls could be designed that could be polarized, even back lit, to blend in with the bottom or with the water. Combined with small powerful computers, ceramic air-independent engines, and the benefits of superconductivity, a relatively light submarine might be produced. This could translate into a boat with impressive submerged endurance and speed.
Flexibility in design also should permit modular construction, allowing for the addition or subtraction of modules as technologies or requirements change. Modules could be exchanged to allow the adaptive packaging of capabilities. Thus, a troop transport module might be exchanged for one containing weapons.
So what might the new attack submarine look like? The Navy should start with the mission the submarine will perform, instead of the boat’s propulsion system, to determine platform design. A boat in the 800-1,400 ton range, with a hull designed for shallow-water employment, is preferable. It should have an overall height less than 20 feet. This could be done by eliminating the conning tower and replacing it with a retractable photonics (visual, infrared, laser) periscope mast. The submarine should be automated to get crew size down to 40 or fewer, as is common with German boats. It should be quiet “enough”—enough for its missions but not the quietest boat that money can buy. It should be able to survive damage. A double hull would be good; the outer hull could protect add-on enhancements or hold fuel and oxidants. For battle damage reasons, it ideally would have more reserve buoyancy than the 13% common in U.S. attack submarines.20
Much of this is contentious, but the Cold War is over and new technologies are available. It is appropriate to reevaluate the character of attack submarines, their missions, and how to execute them. Submarines are essential to littoral warfare. It is time to build boats designed to execute the vision of “Forward . . . From the Sea” aggressively.
1 Brian Longworth, “Changes and Challenges in Underwater Warfare,” Naval Forces, 3(15): 10.
2 U.S. Navy Department, Submarine Operational History, World War II (Washington, DC: 1947), vol. 2, pp. 828-30.
3 Conduct of the Persian Gulf War: Final Report to Congress, Department of Defense, U.S. Government Printing Office, April 1992, p. 282.
4 Richard Humble, Undersea Warfare (London: Basinghall Books, 1981), pp. 91- 92.
5 John Boatman and Mark Hewish, “Naval mine countermeasures,” International Defense Review, 26(July 1993):559-62; and “Strategic plan puts UUVs at the centre of MCM development,” Maritime Defense, 19(5): 112-14. For a discussion of submarines doing mine warfare see Michael J. Baumgartner, “Stay Engaged Through Innovation,” The Submarine Review, July 1993, pp. 65-71.
6 Inside the Navy, 7(12 December 1994):1, 6-7.
7 David Miller, ‘The Silent Menace: diesel-electric submarines in 1993,” International Defense Review, 26(August 1993):613.
8 Richard Humble, Undersea Warfare, p. 87.
9 Bill Gunston, Submarines in Color (New York: Arco Publishing, 1976), pp. 144-45. Also see Anthony Preston, “A New Air Independent Submarine Propulsion System,” Naval Forces, 2(14):62-64.
10 Richard Compton-Hall, Submarine versus Submarine (New York: Orion Books, 1988), p. 26; Ulrich Gabler, Submarine Design (Koblenz: Bernard & Graefe Verlag, 1986), p. 78-81; Gunter Sattler, “Air-independent propulsion: the current state-of-the-art, Defense Systems International '94/95, pp. 128-31; Roy Corlett, “Submarines: the non-nuclear way forward,” in John Moore, ed., Jane’s Naval Review, 1987, pp. 76-83.
11 Hans Harboe-Hansen, “Swedish Submarine Technology,” Naval Forces, 3(15):44- 46.
12 Brian Longworth, Naval Forces, 3(15): 10.
13 Richard Compton-Hall, Submarine versus Submarine, pp. 98-99.
14 Ibid., p. 25.
15 John Boatman and Mark Hewish, “Naval mine countermeasures,” p. 562.
16 David Miller, “The Silent Menace,” p. 616.
17 Norman Polmar, Guide to the Soviet Navy (Annapolis, MD: Naval Institute Press, 1986), p. 152.
18 Montgomery C. Meigs, Slide Rules and Submarines (Washington, DC: National Defense University Press, 1990), pp. 183-85.
19 David Miller, “New Russian Submarine Hunts Export Market," International Defense Review, Vol. 27, p. 51.
20 David Miller, “The Silent Menace,” p. 613.
Commander Murdock, a researcher at the Center for Naval Warfare Studies, Strategic Research Department, U.S. Naval War College, has a master’s degree from the Naval War College. He served as executive officer of the Jarret (FFG-33) during the Gulf War.