The United States Navfs attack submarine force is comprised of multi-purpose nuclear powered attack submarines. FISCal constraints probably wiU reduce the number of submarines which can be built and supported. Proof of this is that Congress funded only one SSN-21 SEA WOLF Class submarine in the FY91 Budget and the Navy requested two. The SSN-21 is the most awesome offensive submarine the world has ever seen, but with the number which probably will be built, the SSN-21 and the follow-on submarines will need to be three times more survivable than the SSN-688 Class submarines. [Ed Note: In repeated Congressional testimony the incumbent OP-02s have stated that SSN-21 will be 3 times as effective as the Improved 688s. Additionally, they have stated that SEA.WOLF will be over 10 times quieter than I-688, have twice the tactical speed, be more survivable and have a significant margin for growth.]
Obviously, as the number of submarines decreases, each one becomes a larger proportion of the United States Navy’s offensive and defensive capabilities. The fleet submarine has become a national asset. This is in great contrast to the fleet submarines of the post-World War II era and earlier. The costs of construction have risen drastically. The most capable submarine cost $6.7 million to build in 1946. The SSN-21 is projected to cost in the billions to build today. The current nuclear powered multi-purpose submarines are much too valuable to allow the loss of even one that could possibly have been saved. The Submarine Force is presently relying heavily on tactics for bringing a submarine out of an engagement successfully. While investing in the men and their ability to fight the ship is essential, there are many other possibilities within reach of current technology for improving the survivability of our submarines.
The U.S. Submarine Force began World War Two with 111 submarines, many of which were obsolete, lost 52 submarines during the four years of war, and commissioned 203 submarines from 7 December 1941 to 1 October 1945. It is obvious that in any future war, the United States could not build as many nuclear submarines in the same amount of time, and losing 52 submarines would decimate the current submarine force. Therefore the U.S. Navy must do everything which is technically feasible to protect its submarines and increase their survival rate in wartime. There are many alternatives for protecting our submarines. Some of these alternatives can be developed and installed on current submarines with minor modifications to the submarine, some alternatives require major structural changes to current submarines, and other alternatives would require whole new submarine designs.
Defenses requiring minor modifications:
(1) a hard kill anti-torpedo device
(2) an anti-aircraft capability
Defenses requiring major structural changes:
(1) stronger hulls
(2) increased number of watertight compartments
Defenses requiring new submarine designs:
(1) double hulls
(2) build smaller submarines .
This list is not all inclusive, but represents alternatives which have been tried or are in use in other navies. Deeper discussion on each of these alternatives is required.
A Hard Kill Anti-Torpedo Device
The research and development for a definitive hard kill antitorpedo weapon would be costly and may not be an efficient use of resources, and some people would say that the capability is not even needed by a modern submarine force. Many others may say, however, that this is a capability which has been overlooked for too long and must be developed by the Navy at any cost. The Navy could spend a billion dollars on this countermeasure and if the result was one submarine surviving a torpedo attack, the cost would be well worth the lives of the crew and the cost of building a replacement submarine. Currently, the U.S. Submarine Force has developed outstanding torpedo evasion maneuvers and has put all the defensive capabilities of our modem submarines in its speed and acoustic countermeasures. As submarine torpedoes become faster and more effective, these defensive capabilities will be less useful. Not to mention the simple truth that the best tactics, speed, and countermeasures in the world will not defend the submarine against a well placed shot from an anti-submarine cruise missile delivered torpedo.
A weapon which will at least give the submarine a good possibility of damaging a helicopter or patrol aircraft is another useful device. There is no weapon currently deployed by any navy which can shoot down a helicopter from a submarine, yet the helicopter remains the primary ASW tool of the surface fleet. Private companies in France and West Germany are currently developing a submarine-launched optically-guided antiaircraft missile, which uses fiber-optics and could be operational in as little as five years. An optically guided anti-aircraft weapon is only one alternative. A simpler and less costly option might be an encapsulated version of the Stinger missile. A Stinger missile variant could be designed to travel some distance underwater prior to surfacing and engaging the aircraft. A submarine detected or close to detection by a helicopter has the option to evade by running away at high speed. This may lead to a solid track for the helicopter and any surface ships or enemy submarines in the area. The enemy would then be able to deploy weapons in the path of the evading U.S. submarine. Imagine the drastic change in tactics by patrol aircraft and helicopters if the submarine they are trying to find has the capability to shoot back. Of course, the same rule for costs of development outweighing the cost of replacing a submarine and her crew apply here just as with the torpedo hard kill device.
This is one area which the U.S. Navy has developed in conflicting directions. The 688 Class had a thinner hull, and therefore a shallower diving depth, but the SSN-21 will be made of higher strength steel to allow for a regain in the operational depth limitations. The SSN-688 hull was designed to be as light as possible to maximize the speed capability of the submarine. While speed is one weapon which any submariner would take to his advantage, another equally advantageous capability would be the greater use of tactical oceanography by allowing a larger envelope of operations, i.e. a thicker skin would allow a deeper depth and give the Commanding Officer the opportunity to exploit the sound conditions to the maximum benefil The depth versus speed trade-off would greatly expand the volume of water in which our submarines can operate, thereby greatly decreasing the delectability and significantly increasing the resources required to find the submarine. The average depth of the oceans is four thousand meters, and the depth limit of our attack submarines allows them the use of only a small fraction of the oceans. While a larger volume of ocean to maneuver in is a great advantage, further studies would be needed to determine if the decrease in speed would put the submarine at a significant disadvantage. Going back to the discussion on the anti-torpedo device shows that developing a hard kill torpedo device could reduce the need for higher speeds. This would allow a stronger, albeit slower submarine hull. Given an anti-torpedo device in conjunction with stronger bulls, the loss of speed should increase the ability of a submarine to tight and survive. Another advantage rarely discussed would be the greater ability to withstand the smaller antisubmarine weapons in use today (i.e. hedgehogs, RBU’s depth charges, etc.).
Increased Number of Watertight Compartments
The U.S. Navy has made one change since the World War Two GATO Qass which has decreased the survivability of our submarines. The SSN-688 Class has only two watertight compartments compared to eight in the GATO aass and five in the STURGEON Class. Realistically this means that uncontrollable flooding will cause certain loss of the crew and the submarine. In the SSN-688 the chance of flooding has been drastically reduced by careful design of the seawater piping, valves, and systems. Ideally the submarine should be able to survive a compartment being flooded and still make it home for repairs, but at the very least a submarine must be able to stay afloat so that the crew has a chance of survival or possibly even repairing the submarine. This capability is almost an afterthought for surface ships designs, watertight integrity allows for major sections to be flooded and the ship can at the least stay afloat and be towed home and may even be able to limp home as the USS SAMUEL B. ROBERTS showed us. A LOS ANGELES Class submarine could not perform this feal The older STURGEON Class is much better designed in this respect, allowing complete flooding of any one of three compartments or a large portion of either of the two major compartments with a good possibility of survival of the crew and the submarine. The best design would be the equivalent of the GATO Class which would allow complete flooding of any one compartment without the loss of the entire ship. These watertight compartments do not have to withstand the pressures at the maximum depth limits. Every submarine officer is trained to bring the ship to a shallower depth in the event of flooding. This means that the bulkheads would only have to be capable of withstanding the pressures of a few hundred feet of water and this would greatly increase the survivability of future submarines.
There are also major advantages to be gained by double hull construction. First and foremost would have to be the added protection of another sheet of non-load bearing steel at a distance from the real hull. This gives significant advantage in regard to RBU’s and hedgehogs, but of course the advantage decreases as the size of their warheads increase. The second advantage to the double hull design would be the greater area for installing exterior weapons and equipment such as countermeasures, vertical launch tubes, and sonar equipment. The ability to change the exterior arrangement without major pressure hull cuts would greatly reduce the costs of research, development, and testing of new weapons and sensors. The third advantage of a double hull would be the larger reserve buoyancies normally associated with double hull submarines. While this is inherently in the design and size of the submarine, double bull submarines lend themselves to higher reserve buoyancies without much effort. A larger reserve buoyancy allows the submarine crew more time on the surface to try to save the ship or at least to get out of the sinking submarine. Lastly, the double hull submarine would allow for a much simpler designed smooth exterior and allow the development of submarines closer to the best length-to-beam ratios and teardrop shapes. This in turn would make up for some of the speed loss due to the extra weight of the steel in the second hull and possibly the weight of a thicker hull and more watertight bulkheads.
Build Smaller Submarines
Reducing the size of the submarine will give rise to three major advantages. The most significant advantage would be the reduction in the target strength of the submarine. The current submarines, being bigger than some smaller new class, naturally present active sonars with large targets and thus an increased probability of detection from these sonar systems. The larger target and easier detection also applies to the active sonar installed in every anti-submarine torpedo. The anechoic coating being installed on our submarines reduces the target strength of the submarine, but attaching the coating to a much smaller submarine could make that submarine virtually undetectable to active sonar systems. This would enable the bold submariner to sneak into an active sonar area which other submarines would have to avoid.
The SSN-21 is the most capable offensive submarine that the United States Navy has ever built and it is undeniably needed as the mainstay of the United States Submarine Force of the future. But more thought needs to be given to the defensive capabilities of our follow-on submarines. There are numerous highly capable submarines and anti-submarine weapons in the possession of the many nations around the world. Our submarine commanders should be able to effectively defend their ship, take the submarine in harm’s way, and then return to the United States. Enhancing the defensive capabilities of the submarine will help to ensure that this is the outcome of future submarine combat patrols.