The T-10 was an American-made version of the Tallboy modified to use standard American components. Development was started in late 1944 and plans were made to drop them on the island strongholds of the Pacific to aid in softening their defences before amphibious assaults. No bombs were used operationally since the capitulation of Japan following the atomic bombings of Hiroshima and Nagasaki negated their need. In the late 1950s the T-10 was re-designated the M-121. During the Korean War a number of T-10s were converted to the radio-guided Tarzon bomb and were dropped by Boeing B-29 Superfortresses to destroy railroad bridges and reservoir dams.