World’s First Underwater Nuclear Explosion
Operation Crossroads was a series of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. It was the first test of a nuclear weapon after the Trinity nuclear test in July 1945, and the first detonation of any nuclear device following the Fat Man detonation on August 9, 1945. Its purpose was to investigate the effect of nuclear weapons on naval ships.
The blast lifted two million tons of water and sand into the air, creating a column 6,000 feet tall, 2,000 feet wide, and with walls 300 feet thick.