The United States conducts the first airborne test of an improved hydrogen bomb, dropping it from a plane over the tiny island of Namu in the Bikini Atoll in the Pacific Ocean on May 21, 1956. (Because of the time difference, it was still May 20 in the U.S.) The successful test indicated that hydrogen bombs were viable airborne weapons and that the arms race had taken another giant leap forward.

The United States began testing nuclear weapons at Bikini Atoll in 1946. However, early bombs were large and unwieldy affairs that were exploded from the ground. The practical application of dropping the weapon over an enemy had been a mere theoretical possibility until a successful test in May 1956. The hydrogen bomb dropped over Bikini Atoll…