The W-50 or W50 thermonuclear warhead was a nuclear bomb used on the MGM-31 Pershing intermediate range nuclear missile. There were two major variants produced (Mod 1, Mod 2), in three yield options (the Y1 with 60 kiloton yield, Y2 with 200 kiloton yield, and Y3 with 400 kiloton yield). All variants were in diameter and long, weighing . The W50 used the Tsetse primary design for its first fission stage, along with several mid and late 1950s designs. The W50 is thought to have been the source of the W78 warhead's fusion second stage design.