It may be time to reconsider a high-low mix of attack submarine types in the U.S. Fleet. In the past the only alternative had been dieselelectric submarines and this was rejected. However the spectrum of choices is now broadened with some of the new “atmosphere independent propulsion” systems being developed in foreign submarine construction yards closed-cycle engines, fuel cells.
Clearly the next generation or “conventional” submarines will have greatly improved operating characteristics — particularly long submerged endurance.
By far the most attractive alternative is the diesel-electric nuclear hybrid submarine, the “SSn”, or the “budget conscious nuc.” Recent research and development in Canada indicates that it may be feasible to develop a small, low-cost nuclear reactor which can be installed in either new construction diesel units or backfitted into some classes of existing conventional submarines.
A Canadian company, Energy Conversion Systems Inc., in the late 1970s was contracted to develop a very simple, low powered (100KWe) nuclear reactor for a research submersible. The reactor system was designated, “Autonomous Marine Propulsion System8 (AMP5-C}.
Although the research submersible program is not yet completed, this work encouraged ECS to consider an enlarged version of their reactor design. Designated AMPS-N, it would have the size and power capacity to be suitable for installation in existing diesel electric submarine designs. This would be done through extending the hull of existing or new design submarines by about 26 feet and adding about 250 tons of weight.
ECS did a computer study of the estimated performance of an AMPs-N installation in a modern diesel electric patrol submarine. The design chosen was the German 1700 ton diesel submarine “T-1700.” The 500 KWe AMPs-N gave a sustained submerged speed of approximately 8 knots while keeping the submarine battery fully charged and carrying the sub’s full “hotel load” power requirements.
The computer model study also showed that the addition of the AMPS-N installation would only increase the cost of a T-1700 by 20% — less than 200 million per copy. Roughly five hybrid versions of the T-1700 could be acquired for the same price as the latest u.s. nuclear attack submarine.
ECS has also done some similar estimates on fitting a slightly uprated version of the AMPS-C into the well known Type 209 submarine (1,0001,400 ton) which was designed by IKL with many built.by HDW in Kiel, Germany.
While no AMPS system has yet been built, tests of many of its technological “building blocks” have been conducted. No real resolution of the claims made for this system can be achieved until a full size prototype is constructed and tested. But enough encouraging preliminary data, modeling results and full scale component testing exist to suggest that this would be an important and valid next developmental step.
Fitting a small nuclear reactor to a modern diesel electric submarine design can offer a formidable operational capability. Contemporary diesel electric submarine designs are very advanced in every respect -w but they need airindependent power plants. Standard reference publications on world submarines give the T-1700 a maximum submerged speed of 24+ knots. or special interest is that this 1700 ton submarine has a crew of only 30. This small crew size is due to advanced automation of many shipboard functions.
New submarine sensors and weapons, developed by several navies, give all modern submarines significant standoff capability when making attacks. In this way speed and range advantages of opponents can be neutralized by the less capable ssn.
The whole idea of technology development of airwindependent engines has been to prolong the time submerged without having to come up for snorkeling. However, each of the systems noted earlier require on-board fuels which limit mission length. On the other hand the small nuclear reactor, such as AMPs-N, does not have any practical operational restrictions with respect to fuel.
How would a high-low mix of SSN’s and SSn’s support the submarine mission requirements for a large modern navy? Clearly the SSN’s would be optimum for open ocean and distant ocean operations where speed, more sophisticated systems and endurance are required. The ssn could be used foroperations where these factors were less important.
Some examples of missions would be:
- Choke Point Patrols. This would mean operating in the vicinity of straits and other restricted transit areas where enemy submarines and surface ships might be expected to pass. If the SSA required to quickly close a target it could use its battery to achieve speeds sufficient for this purpose. In case of a combat situation, the submarine’s standoff weapons could make up for any significant speed differences between the ssn and the transiter.
- Under Ice Operations. This is also an area of submarine operations where endurance, stealth and good sensors are more valuable than high speeds.
- Antiship Operations. The hybrid submarine would be quite effective against enemy shipping in logistics interdiction, as well as against less capable warships.
- Special Warfare Operatic~ These missions would involve the covert use of underwater swimmers (i.e., the USN SEAL teams) who would be launched and recovered nearshore off enemy coastlines. In addition the SSn would make an excellent platform for intelligence gathering operations.
There are undoubtedly many more missions that could be undertaken by the SSn; these would become more evident as these submarines came into service.
There are difficult questions that must be answered in developing this type of reactor and as power levels are increased, their relative simplicity will be rapidly reduced. Technical, cost and safety tradeoffs must be studied more closely. Lifetime support costs for these reactors, including disposal of waste materials,
must be factored into overall cost projections. But enough data exists at this point to strongly support the development of a full scale land based prototype with subsequent installation in an existing submarine hull if the prototype meets its design specifications.
It’s important to note that the world’s best submarine may not be needed for every Navy mission. Also it may not be affordable in the numbers necessary to cover every mission requirement. Recalling the words of the great airpower advocate, Alexander de Seversky, “Quantity is itself a quality.” This may be the case for USN planhihg as it considers its submarine mission requirements for the 21st Century.
Clearly it is time for the U.S. Navy to reconsider whether or not it could benefit from having a high-low mix of attack submarine assets consisting of SSNs and ssns.
Dr. Don Walsh, Ph.D
Editorial Review Board Comment: The Naval Submarine League’s policy is not to prohibit the publication of articles that express various views or perceptions if the article is substantive in content. This publication in no way should imply NSL sanction or endorsement.