[Smaragdadler]

AIP - The Early History


Walter Type XVIIB up on the stocks. Pictured above is the German Walter Type XVIIB U-1406, partially dismantled shortly after the end of World War II. U-1406 was turned over to the U.S. Navy as a war prize and soon disposed of, but the Royal Navy later operated her sister ship, U-1407, as HMS Meteorite to gain experience in hydrogen-peroxide propulsion technologies.

Despite their initial successes, submarine pioneers were still eager to find some means to free their boats from the necessity of surfacing frequently for access to the atmospheric oxygen demanded by the gasoline or diesel engines that charged the batteries. A number of approaches were tried, but eventually, open-cycle diesel engines, lead-acid batteries, and electric motors for submerged propulsion became the standard submarine engineering plant that served well through two world wars.

In the early 1930s, however, a brilliant German engineer, Dr. Helmuth Walter (ca. 1900-1980) of Kiel's Germaniawerft, proposed a radical new submarine propulsion plant based on the use of high-purity hydrogen peroxide (H2O2) as an oxidant. In Walter's system, hydrogen peroxide from an onboard supply was decomposed using a permanganate catalyst to yield high temperature steam and free oxygen. Into the reaction chamber was injected diesel fuel, which combusted with the oxygen to yield a mixture of steam and hot gas that drove a high-speed turbine. The exhaust and condensed steam were then expelled overboard. Walter's primary design goal was high underwater speed, rather than long endurance, and indeed, his first submarine prototype, the experimental V80, reached 28.1 knots submerged in its 1940 trials - at a time when conventional submarines were limited to 10 knots or less. Thus, V80, only 76 tons and 22 meters long, also served as an early test bed for studying the dynamics and control of high-speed underwater vehicles.

Later in the war, the Kriegsmarine attempted to scale Walter's prototype up to a useful operational size, but although seven Type XVIIB H2O2 coastal boats were completed before Germany's final defeat, none saw combat. These Type XVIIs displaced 300 tons and were powered by two 2,500 horsepower turbines, in addition to a conventional diesel-electric plant. More ambitious plans to build larger Walter-designed ocean-going submarines, such as the 800-ton Type XXVI and the 1,600-ton Type XVIII were thwarted by the unsuccessful course of the war and the realization that the industrial capacity needed to supply sufficient quantities of hydrogen peroxide could never be achieved. However, the Type XVIII was modified into the highly successful Type XXI "electro-boat," in which larger batteries provided a submerged speed of 17 knots, which could be maintained for 90 minutes. That innovation, and the adoption of the snorkel, yielded a potent combination that strongly influenced the postwar design of conventionally-powered submarines on both sides of the Iron Curtain.

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An AIP Perspective
Although it is a remarkable tribute to Hellmuth Walter's engineering genius that he fielded a fully functional - if troublesome - 5,000-horsepower AIP system in 1945, the maximum power output of current AIP installations is typically on the order of 400 horsepower (300 kilowatts). In comparison, the conventional diesel-electric plant of the U 212 class described above is rated at over 3,000 horsepower, and a typical nuclear submarine propulsion plant produces over 20,000. Since the power required to propel a submerged body varies with the cube of its velocity, it should be apparent that at least for the near future, AIP will be valuable primarily as a low-speed, long-endurance adjunct to the under- water performance of conventional submarines. There is little short-term prospect for AIP to become a primary, full-performance alternative to either diesel or nuclear power. Even the phrase "closed cycle" is something of a misnomer, because except for fuel cells, all AIP alternatives require ejecting exhaust gases overboard, which limits both depth capability and stealth.

However, this is not to minimize the dangerous potential for AIP submarines to complicate seriously both coastal defense and assured access to littoral regions. If their distinctive characteristics are exploited by skillful operators, AIP submarines can be used to telling effect for both short- and medium-range missions. AIP dramatically expands the tactical "trade-space" for diesel-electric submarines. If conditions permit, they can transit rapidly on the surface with-out unduly expending the wherewithal for superior underwater performance. Submerged, they can opt for a long, slow, silent patrol that keeps their batteries fully charged and thus capable of powering speed bursts of significant duration. And by carefully husbanding their resources, they can revert again to slow-speed operation and repeat the cycle several times over weeks of submergence. Moreover, AIP technology is evolving rapidly, and some experts predict, for example, that the power output of a typical fuel cell module could well double or triple in the next several years, allowing an even more advantageous trade-off between underwater speed and endurance.

Their tactical flexibility, their small size, their inherent stealth - and the novel operational paradigms AIP submarines introduce to undersea warfare - will make these new boats a dangerous threat to submariners accustomed to nuclear- or conventionally diesel-powered adversaries. The Submarine Force needs to understand this threat - where it's been, where it's going, what it means, and how to counter it.

more:
http://www.chinfo.navy.mil/navpalib/...propulsion.htm