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Editor’s Note: lieutenant Hanna’s paper Won the Naval Submarine League Essay Contest for Submarine Officers’ Advanced Dass 99030. lieutenant Hanna is currently the Executive Officer on NR-1.

You may be thinking that an SSN already has an air independent propulsion (AIP) system powered by its nuclear reactor; however, you would only be partially correct. While the reactor is the primary power source, a diesel engine with attached generator is the alternate means for long-term emergency power. This diesel engine is not an ideal alternative power source to the react. or and there is the better technology being developed.

The Problem

As a power source, the diesel has some major tactical deficiencies. As an air dependent system, the diesel is not available on demand at any operating depth of the submarine. Instead, the submarine must have access to external air through either the snorkel mast or an open hatch for the diesel to run. In arctic areas, the requirement for external air could create serious consequences if ice-free water is not immediately available. In addition, the demand for snorkel air would create a very long and dangerous trip home, if the diesel becomes the sole means of recharging the batteries and providing propulsion. Because of the air dependency, the submarine must risk non-acoustic counter-detection by exposing a large radar cross-section in order to gain the air for the diesel. On some peacetime missions, a counter-detection could have serious political ramifications and during wartime, it may mean death for the submarine and her crew. Along with the non-acoustic counter-detection risk, the diesel is a serious acoustic counter detection risk. The diesel operations are not as quiet as operating on the reactor and provide a significant acoustic source. In summary, the diesel provides the SSN three major problems during an emergency, 1) air dependent, 2) non-acoustic counter-detection risk, and 3) an acoustic counter-detection risk.

The Solution

There is a new technology that is on the near horizon {less than 5 years away) which can solve all the problems of the diesel and provide some additional benefits. The technology is air independent propulsion power provided by hydrogen-oxygen cells. This technology is under development by the Germans for incorporation into the Type 212 SSK in the year 2005. The cells work on a (Process similar to running an oxygen generator in reverse. Hydrogen and oxygen are mixed in a cell with a catalyst and recombine into water while directly producing electricity. There is no combustion and no motor or generator required. The cells are expected to be extremely safe (it is anticipated that Mercedes Benz will even use these cells in consumer vehicles, i.e., cars and trucks). The AIP system will give the U-Boats an ability to operate for over IO days submerged and could possibly provide an SSN with the same sort of ability as a substitute for the diesel generator.

Hydrogen-oxygen cells have many advantages. To begin with, they address all the concerns of the diesel generator. They would be an on-demand alternate power source able to provide long-term emergency power without the need for external air. They remove both the non-acoustic and acoustic detection opportunities associated with the current diesel.

AIP technology has the ability to provide more advantages than just fixing the diesel. A possible tactical advantage of AIP would be as a means to gain a few dB of acoustic advantage by shutting down the reactor and associated systems. Of course, the CO would have to weigh the acoustic advantage gained with his corresponding loss in maximum propulsion capability; however, with careful considerations a quick-start ability to shift back to nuclear propulsion and evade could be safely devised.

In addition to tactical advantages, hydrogen-oxygen cells have the prospect for some significant side benefits. installation of AIP would necessitate the removal of the diesel and the associated equipment. If the AIP cells were an integral part of an SSN’s design, then several hull penetrations and their associated sub safe systems currently required for the diesel could be removed. The removal of these hull penetrations could help allay some of the costs of installing AIP and, at the very least, increase hull integrity. Along with the removal of systems, the hydrogen-oxygen cells should contain significantly less moving parts when compared to the diesel. The reduction in moving parts likely would allow a reduction in the required PMS and associated long-term costs of operating the system. In addition to reducing systems and maintenance, the AIP system should reduce operators. At a minimum reduction, there will be no need for a sump watch and at a maximum reduction, the system might even be designed such that the Electrical Operator could push a button and have power. Of course, this would also entail removing the current test of manliness-priming the diesel. The last side benefit of hydrogenoxygen cell technology is the possibility that it may help the Navy meet even tougher environmental regulations. For example, diesel lube oil and diesel fuel would be removed. In addition, water is the waste product of the AIP cell and could be used on board or pumped safely overboard. The last benefit of the cells may not be realistic; however, it should be examined. The SSN’s oxygen generator could function as a means of recharging the hydrogenoxygen cells; thereby creating almost a virtual hydrogen-oxygen battery able to be used during drills or actual events and recharged at will.


While there are bound to be some drawbacks with any new systems (such as a safe means to store the hydrogen and the oxygen), the hydrogen-oxygen cell provides a significantly better alternative power source for an SSN when compared with the diesel. Working with Germany, the United States should develop AIP technology for inclusion in latter Virginia class SSNs and the post-Virginia class SSN.

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