May 20th 1956; 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. The successful test indicated that hydrogen bombs were viable airborne weapons and that the arms race had taken another giant leap forward.  The massive open-air blast in 1956 caused concerns among scientists and environmentalists about the effects of such testing on human and animal life. During the coming years, a growing movement in the United States and elsewhere began to push for a ban on open-air atomic testing. The Limited Test Ban Treaty, signed in 1963 by the United States, the Soviet Union, and Great Britain, prohibited open-air and underwater nuclear testing.