Bikini Atoll mushroom cloud

Suspended 90 feet below the sea, anchored beneath an auxiliary craft in the midst of the target ghost fleet, the detonation of Test Baker marked the first-ever underwater nuclear explosion when the 23 kiloton device was detonated on July 25, 1946, at the Bikini Atoll lagoon, Marshall Islands, in the Pacific Ocean. 

The device, which displaced 2 million tons of water, was the fifth of over 2,000 nuclear explosions conducted to date by the U.S. military. Only a few of the tests were underwater explosions, carried out primarily to research the impact to ships and submarines. 


Test Baker, and Test Able on July 1, 1946, were part of "Operation Crossroads," a series of nuclear tests conducted during 1946. The massive project sought to answer questions about the effects of nuclear weapons on a fleet of ships and living animals. The operation involved 42,000 personnel, 242 ships, 156 airplanes, and the relocation of all 162 residents from the Bikini Atoll. 

The Marshall Islands became quite familiar with the nuclear studies of the U.S. military. The Bikini Atoll became the site of another nuclear first when a B-52 dropped the first airborne hydrogen bomb on May 21, 1956. 

The mushroom cloud and water column seen here resulted from the underwater Test Baker nuclear explosion of July 25, 1946, as seen from an observation tower on Bikini Island, 3.5 miles away from ground zero. PHOTOS