Post War German Submarine Legacy

In the fall of 1945, the victorious Allies faced a series of issues. The first was the newly developed atomic bomb and what it portended for future wars, and specifically if in time atomic power could not only be harnessed to propel submarines, but to deliver atomic weapons from them. The second was the growing tension between the United States, Britain, and the Soviet Union, which would soon become an undeclared “cold war,” and the role that submarines would play in this. Another issue was the next steps in the development of the submarine.

The United States, Britain, and the Soviet Union possessed fleets of submarines that had just helped them win the world war. Other powers also possessed submarines, though not to the same extent. Yet all of these submarines were, while suited for the undersea war just fought, not ideal for any future conflict. Wartime experience had shown that the next generation of submarines had to be faster, quieter, spend less time exposed and vulnerable on the surface, and be capable of diving deeper than subs had hitherto gone. Consideration also needed to be given to the new types of weapons, particularly rockets and missiles, and how they could be adapted to submarines. In addition, a new oceanic strategic frontier, the Arctic, had opened during the war, and future conflicts might well require submarines that could extensively navigate and fight beneath the ice.

For some of the winning powers, particularly the United States, there was also a necessary reduction in force to be weighed, as hundreds of boats were no longer needed and wartime reservists, volunteers, and draftees were returning to civilian life. There was also the matter of the large numbers of captured German U-boats and Japanese submarines, including hundreds of incomplete Midgets and Kaiten, and how to assess their technologies effectively while also quickly demilitarizing the former Axis powers. One technology that the United States wished to assess was the snorkel as adapted by the U-Bootwaffe, as well as superior German hydrophones, specialized anti-sonar rubber coatings for U-boat hulls, and an alternate method of powering a submarine, the Walter engine.

The Walter, named for its inventor, Hellmuth Walter (1900–80), was an air independent system for propulsion (AIP). While earlier inventors such as Payerne, Monturiol, and others had worked with a variety of AIP systems, Walter’s early work with marine engines suggested that an oxygen-rich fuel would negate the need for an external air supply or air from tanks. The source Walter settled on was hydrogen peroxide, which with the right catalyst (permanganate of lime) spontaneously combusted to release oxygen and high-temperature, high-pressure steam. Walter patented his research in 1925, and later, in 1940, used it to develop an experimental submarine. That craft, the V-80, was a 76-ton, four-man submarine capable of reaching 28 knots submerged.

From these beginnings, Walter’s propulsion system was integrated into larger U-boats, Type XVII craft. Three of these boats, U-1405, U-1406, and U-1407, were completed by the war’s end, with two others still under construction. The Type XVIIs also featured a more hydrodynamic hull form to reduce drag and increase speed, and in trials they reached 22–23 knots while submerged. Another advanced U-boat class, the Type XXI, also a streamlined, hydrodynamic craft, had three times the battery capacity of a Type VII, and was capable of running completely submerged for two to three days before recharging, which was done submerged by extending the snorkel and running the diesels for about five hours. These “elektroboote” represented yet another innovative German design that the war’s end had prevented the Nazis from deploying in large numbers – only two went on combat patrol. The advanced U-boats, however, played a role in determining the submarine designs of the future for the victors of the war.

The captured boats

While their crews scuttled a number of U-boats at the end of the war, a large number of boats, some of them not yet completed and still in the yards, were surrendered to the Allies. In all, some 154 U-boats made their way into Allied hands. Several were studied carefully, while others were assembled and sunk during Operation Deadlight between late 1945 and early 1946. In all, the British scuttled 121 U-boats off Lisahally, Northern Ireland, the last being U-3514, sunk by gunfire and an experimental antisubmarine weapon in Loch Ryan on February 12, 1946. Others were sunk later, such as U-1105, a modified Type VIIC boat covered with a rubber skin to foil Allied sonar. After transfer to the United States and testing in Chesapeake Bay, the US Navy used a depth charge to sink U-1105 off Piney Point, Maryland, in September 1949. The United States also examined a variety of captured Japanese craft, including four I-boats, among them the giant seaplane-carrying submarines I-400 and I-401, all scuttled off the coast of Hawaii in the spring and summer of 1946. A handful of Midgets and Kaiten were also examined, and a few were saved as war trophies, while hundreds of other smaller Japanese subs including Kairyu and Kaiten were destroyed with demolition charges and scrapped.

Among the U-boats examined by the Allies were eight boats surrendered to the Royal Navy and subjected to tests by the British, notably the Type XXVII boat U-1407, which the Navy commissioned as HMS Meteorite to test its Walter propulsion system, and retained in the fleet until 1949. Based on these trials, the British built two experimental boats, HMS Explorer and HMS Excalibur in 1954 and 1955. The United States took two surrendered U-boats, the Type XXI boats U-2513 and U-3008, commissioned them with American crews, and tested them in 1946–48 to learn more about the secrets behind their fast speeds. The effort was high profile; in December 1947, President Harry Truman visited U-2513 at Key West, Florida, becoming the second American President (Theodore Roosevelt was the first) to ride on a submarine.

When the tests were completed, the boats were scuttled, U-2513 by rockets off Key West, Florida, in September 1951 and U-3008 off Roosevelt Roads, Puerto Rico, in 1954. It was subsequently raised and sold for scrap in 1956. The result of the American tests of the German U-boats was the Greater Underwater Propulsion Project, or GUPPY. While the GUPPY project and its British counterpart were still on the drawing board, however, the US focused its attention on the question of the atomic bomb and the submarine.

The Royal Navy, in addition to building its own two versions of the Type XXVII U-boat, also launched a streamlining program of its large wartime S- and T-class submarines in the 1940s and 1950s. Two new classes of diesel-electric boats were designed that would gradually replace the warhorse S- and T-boats. The first was the Porpoise class of 1955, and the second was the Oberon class of 1959. Britain launched eight Porpoises between 1956 and 1959, when the Oberons replaced them, and launched 27 of the latter for service in the navies of the UK, Australia, Canada, Brazil, and Chile. Modeled after the Type XXI, the Porpoise boats were 290ft long, displaced 2,080 tons, and were powered by two Admiralty standard range 16-cylinder diesel generator sets (with snorkel) and 5,000hp electric motors capable of reaching 12 knots on the surface and 17 knots submerged. With all-welded construction and improved steel for the hull, the Porpoises could dive deeper, had a patrol endurance of 9,000 nautical miles, and were also fitted with an oxygen replenishment system with carbon dioxide and hydrogen scrubbers to enable them to stay submerged for days – and up to six weeks with their snorkel deployed. The first Oberons, launched between 1959 and 1964, were basically improved versions of the Porpoise, with tougher steel hulls for deeper diving, better detection equipment, and the use of fiberglass – a first in British subs – in their streamlined superstructures. Additional boats built after 1964 included those for foreign states, and a number remained in service through 1988.

The American experience followed that of the British, focusing on greater speed for submarines both on the surface and submerged – and the necessary changes to both hull form and propulsion systems to increase speed. The wartime Balao and late-war Tench classes had served well, but were too slow and had insufficient range when submerged for the postwar mission of the US Navy, which was increasingly seen as a likely confrontation with the Soviet Union, either through the Cold War or a scenario where the “cold” war turned into a hot one. The Soviets had captured a number of advanced U-boats, were assessing the Type XXI boats and Walter engines, and their prewar build-up of a submarine force suggested a postwar program to build advanced submarines in large numbers was inevitable. This posed a threat that the United States was ill-prepared to deal with, especially if large numbers of Soviet submarines found a way to make a transpolar approach under the Arctic ice, or they poured faster, less exposed boats in large numbers into the North Atlantic and North Pacific from submarine bases.

Greater Underwater Propulsion Project (GUPPY)

The Greater Underwater Propulsion Project (GUPPY) to modify the submarine fleet was inaugurated to start to meet the challenge, while naval designers also determined the form of the next generation of American submarines. Two Balao class boats, USS Odax and USS Pomodon, were the first “Guppy” boats, and their conversion, completed by 1947, involved removing anything that created flow resistance on the hull, including the deck gun and the wooden deck, enclosing the conning-tower and bridge in a streamlined “sail” (known as a “fin” to the British), smoothing the lines of the bow, folding in the bow planes, and also increasing battery capacity for greater underwater endurance. The removal of the boats’ auxiliary diesel engine and generator, and the ammunition magazine for the deck gun, and the reorganization of some compartments provided the necessary room.

While there were “bugs” to work out, the first Guppies’ flow resistance had been cut by 50 percent. Later Guppy II modifications added a retractable snorkel, new higher-capacity batteries, additional air-conditioning to handle increased heat in the boats, and new sonars; in the 1960s, the Guppy III program cut older boats in half and added a 15ft section housing then modern electronic and fire-control systems that increased their length to 327ft and surface displacement to 1,731 tons. Guppy III modifications also added a larger fiberglass sail and three domes for PUFFS (BQG-4) passive ranging sonar. In all, 55 submarines underwent Guppy conversion, four of them for transfer to Italy and the Netherlands. In addition, 19 other boats underwent a lesser modification as “fleet snorkel conversions,” while other boats were modified and converted to a range of different categories – cargo (SSA), guided-missile (SGA), hunter-killer (SSK), transports (SSP), radar pickets (SSR), targets (SST), and miscellaneous auxiliaries (AGSS). In this fashion, the US Navy retained a number of its wartime boats well into the 1960s and early 1970s. It decommissioned its last wartime-built submarine, the Guppy II-converted USS Tiru, on July 1, 1975.

While US Guppies were transferred to some powers, others, including France, pursued their own fast designs. The French Navy received three U-boats at the end of World War II, including a Type XXI and a Type XXIII. The Type XXI, U-2518, was recommissioned as Roland Morillot in 1951 and served until 1967. Working with what they had learned from operating Morillot, the French then designed the Narval class, and launched six of these fast diesel-electric boats between 1957 and 1960. The Narvals continued to serve into the 1980s, and made a series of noteworthy missions to demonstrate submerged endurance and under-ice Arctic incursions to 72 degrees north.

The Soviet Union also pursued faster submarines, drawing on the design of captured U-boats. Six Type XXI boats transferred to the Soviets after the war were recommissioned, along with four Type VII U-boats, to serve in the Soviet Navy. Soviet designs followed the diesel-electric model with Project 611 (NATO codename Zulu) boats. Based again on the lessons learnt from the Type XXI, the Zulus were 295ft-long, 1,875-ton, streamlined, fast boats with increased battery-power that gave them speeds of 16 knots submerged and 18 knots on the surface. Between 1952 and 1957, the Soviets placed 26 Zulus in service, and in 1956, modified six of them to fire a single R-11 (NATO codename SCUD) missile, making these the world’s first ballistic missile submarines. The next diesel-electric Soviet submarine class, the 1958 Project 629 (NATO codename Golf), introduced larger, 2,794-ton boats with inbuilt missile silos, but at that time the Soviet Union was pursuing another trend – the nuclear-powered submarine.

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