The Allies called for the unconditional surrender of the Imperial Japanese armed forces in the Potsdam Declaration on 26 July 1945, the alternative being 'prompt and utter destruction'.
The 509th Composite Group of the United States Army Air Forces was trained and equipped with the specialized Silverplate version of the Boeing B-29 Superfortress, and deployed to Tinian in the Mariana Islands. By July 1945, the Allies' Manhattan Project had produced two types of atomic bombs: 'Fat Man', a plutonium implosion-type nuclear weapon and 'Little Boy', an enriched uranium gun-type fission weapon. The war in Europe concluded when Germany surrendered on, and the Allies turned their full attention to the Pacific War. This undertaking was preceded by a conventional and firebombing campaign that devastated 67 Japanese cities. In the final year of World War II, the Allies prepared for a costly invasion of the Japanese mainland. The two bombings killed between 129,000 and 226,000 people, most of whom were civilians, and remain the only use of nuclear weapons in armed conflict. The United States detonated two nuclear weapons over the Japanese cities of Hiroshima and Nagasaki on 6 and 9 August 1945, respectively.
