World War II Allies invasion of the Japanese mainland conventional bombing and firebombing campaign war in the European theatre surrendered Pacific War Manhattan Project Little Boy enriched uranium gun-type fission weapon Fat Man plutonium implosion-type nuclear weapon 509th Composite Group United States Army Air Forces Silverplate Boeing B-29 Superfortress Tinian Mariana Islands unconditional surrender Imperial Japanese armed forces Potsdam Declaration ignored atomic bombs
In the final year of World War II, the Allies prepared for a costly invasion of the Japanese mainland. This undertaking was preceded by a conventional bombing and firebombing campaign that devastated 64 Japanese cities. The war in the European theatre concluded when Germany surrendered on 8 May 1945, and the Allies turned their full attention to the Pacific War. By July 1945, the Allies' Manhattan Project had produced two types of atomic bombs: "Little Boy", an enriched uranium gun-type fission weapon, and "Fat Man", a plutonium implosion-type nuclear weapon. 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. 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 Japanese government ignored the ultimatum.
