The Royal Navy's T class (or Triton class) of diesel-electric submarines was designed in the 1930s to replace the O, P, and R classes. Fifty-three members of the class were built just before and during the Second World War, where they played a major role in the Royal Navy's submarine operations. Four boats in service with the Royal Netherlands Navy were known as the Zwaardvisch class. In the decade following the war, the oldest surviving boats were scrapped and the remainder converted to anti-submarine vessels to counter the growing Soviet submarine threat. The Royal Navy disposed of its last operational boat in 1969, although it retained one permanently moored as a static training submarine until 1974. The last surviving boat, serving in the Israel Sea Corps, was scrapped in 1977. Development The design of what was to become the T class began in 1934 in order to create a replacement for the first British postwar submarines, the O, P, and R classes. These similar classes of submarines had proved unsatisfactory, being mechanically unreliable, large, slow, and overcomplicated. Furthermore, the Washington Naval Treaty of 1922 required that these submarines be retired after 13 years of service. Thus, would have to be paid off in August 1940 (in the event, the outbreak of war in 1939 kept her in service). The 1930 London Naval Treaty restricted the British submarine fleet to a total tonnage of 52,700 tons, a maximum standard surfaced displacement of 2,000 tons for any boat, and maximum gun armament of . The Americans had proposed a limit of 1,200 tons for the 1935 London Disarmament Conference, but this was rejected by the Admiralty since it would exclude the mine-laying submarines. The Admiralty itself proposed retaining the limit of 2,000 tons, hoping that the rival naval powers would build fewer but larger submarines as a matter of national pride, which would be easier to hunt down than numerous smaller submarines. The Conservative government of Stanley Baldwin had also proposed banning the submarine altogether or imposing an individual displacement limit of 250 tons, but the Admiralty correctly predicted that the other nations would not accept such strict limitations and continued with the design of what was then known as the "Repeat P" or "Replace P" class of submarines. The O, P, and R classes had been designed with the Pacific in mind as a counter to the increasingly powerful Imperial Japanese