The U.S. refused to supply the Soviet Union with B-29 heavy bombers under Lend Lease, despite repeated Soviet requests. However, on three occasions during 1944, individual B-29s made emergency landings in Soviet territory after bombing raids on Japanese Manchuria and Japan. In accordance with the Soviet–Japanese Neutrality Pact, the Soviets were neutral in the Pacific War and the bombers were therefore interned and kept by the Soviets, despite American demands for their return. Stalin tasked Tupolev with cloning the Superfortress and Soviet industry was to produce 20 copies of the aircraft in just two years.