for active service during the Suez Crisis in 1956, and remained in commission until 1967. It was scrapped in 1969. Soviet Union Four Type XXI boats were assigned to the USSR by the Potsdam Agreement; these were , , , and , which were commissioned into the Soviet Navy as , , B-29, and (later B-100) respectively. However, Western intelligence believed the Soviets had acquired several more Type XXI boats; a review by the U.S. Joint Intelligence Committee for the Joint Chiefs of Staff during January 1948 estimated the Soviet Navy then had 15 Type XXIs operational, could complete construction of 6 more within 2 months, and could build another 39 within a year and a half from prefabricated sections, since several factories producing Type XXI components and the assembly yard at Danzig had been captured by the Soviets at the end of World War II. U-3538 — U-3557 (respectively TS-5 – TS-19 and TS-32 – TS-38) remained incomplete at Danzig and were scrapped or sunk during 1947. The four boats assigned by Potsdam were used in trials and tests until 1955, then scuttled or used for weapon testing between 1958 and 1973. The Type XXI design formed the basis for several Soviet design projects, Projects 611, 613, 614, 633, and 644. These became the submarine classes known by their NATO codes as , and submarine classes. United Kingdom was commissioned into the Royal Navy as . It was used for tests until being scrapped during November 1949. United States The United States Navy acquired and , operating them both in the Atlantic Ocean. During November 1946 President Harry S. Truman visited U-2513; the submarine dived to with the President aboard. U-2513 was sunk as a target on 7 October 1951; U-3008 was sold for scrap on 15 September 1955. Survivor The only boat to survive intact is (ex-U-2540), at the German Maritime Museum in Bremerhaven. Records indicate that this sub was scuttled by its crew in 1945, salvaged in 1957 and refurbished for use by the West German Bundesmarine until retirement in 1982. It was then modified to appear in wartime configuration for exhibition purposes. Notable wrecks The wrecks of several Type XXI boats are known to exist. During 1985, it was discovered that the partially scrapped remains of , , and were still in the partially demolished "Elbe II" U-boat bunker in Hamburg. The bunker has since been