Federal Government and User:Anynobody. Linked source: Wikipedia image http://en.wikipedia.org/wiki/File:Nukecloud.png . Permission: Public domain at least in USA . The Little Boy nuclear bomb used at Hiroshima was 15 kt. Castle Bravo test at Bikini Atoll in 1954 was the biggest test US nuclear bomb at 15 Mt---earlier tests at Bikini inadvertantly