Boeing submitted the prototype for the B-29 long-range heavy bomber to the Army in 1939, before the United States entered World War II. The B-29 had many new features, including guns that could be fired by remote control. The crew areas were pressurized and connected by a long tube over the bomb bays. The tail gunner had a separate pressurized area that could only be left during unpressurized flight. The B-29 was also the heaviest production plane because of increases in range, bomb load and defensive requirements. B-29s were primarily used in the Pacific theater during World War II. As many as 1,000 Superfortresses at a time bombed Tokyo, destroying large parts of the city. Finally, on Aug. 6, 1945, the B-29 Enola Gay dropped the world's first atomic bomb on Hiroshima, Japan. Three days later a second B-29, Bockscar, dropped another atomic bomb on Nagasaki. Shortly thereafter, Japan surrendered. After the war, B-29s were adapted for several functions, including in-flight refueling, anti-submarine patrol, weather reconnaissance and rescue duty. The B-29 saw military service again in Korea between 1950 and 1953, battling new adversaries: jet fighters and electronic weapons. Production ended in 1946. The last B-29 in squadron use retired from service in September 1960.