W49

The MK43, W44, W50, MK57, and W59 share a common "Tsetse" primary. Both the "Tsetse" and "Python" primaries were plagued by a tritium cross-section miscalculation uncovered during the early 1960s, after the nuclear testing moratorium ended.

The Starfish Prime test took place on July 9, 1962. A Thor rocket was launched from Johnston Island carrying a 1.45 megaton W49 thermonuclear warhead. When the warhead detonated at a height of 248 miles, it unexpectedly lit up the night skies all over Hawaii hundreds of miles away for six minutes.