HDW's fuel cell uses liquid oxygen (LOX) and hydrogen as reactants to produce electricity from the cell. Hydrogen is stored in a metal-hydride matrix, with it and the LOX carried outside the single-compartment pressure hull. The submarine is equally quiet operating on the battery or AIP. A fuel cell does not have a high rate of energy delivery, so high speed (greater than 8 knots) requires using the battery for sprinting. Then while drifting the fuel cell tops up the battery.
The Thyssen closed-cycle diesel system operates a conventional diesel engine using liquid oxygen, argon gas, and diesel fuel. Basically the closed-cycle system "manufactures" air from the oxygen and argon to burn the diesel fuel. Then the exhaust gas is scrubbed to separate the carbon monoxide and carbon dioxide (which are soluble in seawater) and it is exhausted overboard, using a valving system that is depth-insensitive. The inert argon provides the proper density for the manufactured air and is recovered almost entirely during the cycle. Tests on the ex-U-1 showed that this system was extremely quiet during submerged operations. The closed-cycle diesel is somewhat less costly than the fuel cell system.
The latest from the GSC is the remarkable Type-212 class. In development since 1994, the first will go into service with the German Navy in 2003, as their first hybrid submarine. The fuel cell AIP system will be standard, together with a more conventional diesel-electric propulsion system. The design goal is to permit submerged cruising for up to 3,000 miles at 4 knots. This means the Type-212 can remain submerged and quiet for more than a month.
Four Type-212s will be built for the German Navy, two each by HDW and Thyssen. Italy will build two (with an option for two more) at the Fincantieri Shipbuilding Company, using drawings provided by German Submarine Consortium. Other navies are interested in this submarine, though their identities are kept confidential at this time. The approximate unit price of a Type-212 is a budget-friendly $250 million.
In addition to the advanced propulsion system, the Type-212 will have several other important technical features. Its main propulsion motor will be a slow-turning, direct drive permanent magnetic alternating current motor developed by Siemens. It is about half the size of a similar rated direct-current motor. Austenitic steel will be used for the pressure hull making it virtually non-magnetic, a development that HDW and Thyssen have been working on for nearly 30 years. Also, every item put on board is made as non-magnetic as possible. A completely integrated ship control, navigation, and weapon system permits highly automated operations-so the 1,350 ton Type-212s can operate with a crew of only 24. Six forward torpedo tubes are operated by a virtually noiseless water-ram hydraulic expulsion system, which permits firing of torpedoes or encapsulated missiles—even when the submarine is bottomed.
Germany is not alone in offering AIP options. Other classes are: France's Agosta ; Holland's Walrus ; Russia's Kilo "Design 626" (and upcoming Amur ), and Sweden's Gotlands . Not all use the fuel cell or closed-cycle diesel for their AIP systems. Sweden's three Gotlands use a Stirling cycle engine as standard equipment, while the French offer the Mesma steam turbine system with LOX and ethanol as the reactants. Pakistan will join the ‘AIP fraternity' when the last of its three, Frenchbuilt Agosta -class submarines is delivered. It will have the French Mesma AIP.
Introduction of the Type-212 class in 2003 will most certainly force the world's naval planners to reconsider seriously the diesel submarine theat. Perhaps the U.S. Navy should procure an ‘aggressor squadron' of Type-212s, to learn how to counter a truly sneaky diesel boat.