The B83 thermonuclear weapon is a variable-yield gravity bomb developed by the United States in the late 1970s, entering service in 1983. With a maximum yield of 1.2 megatonnes of TNT (5.0 PJ) (75 times the yield of the atomic bomb "Little Boy" dropped on Hiroshima on 6 August 1945, which had a yield of 16 kilotonnes of TNT (67 TJ)), it is the most powerful nuclear free-fall weapon in the United States arsenal.[1] It was designed at Lawrence Livermore National Laboratory, and the first underground test detonation of the production B83 took place on 15 December 1984.[2]