Operation Crossroads were the fourth and fifth nuclear explosions in history, after the Trinity test and the atomic bombing of Hiroshima and Nagasaki. The two detonations were called Able and Baker. The detonations were similar in yield to the Trinity test (20 kilotons of TNT equivalent), Hiroshima (13 kt) and Nagasaki (21 kt), with a yield of 21 kt for Able and 23 kt for Baker. Operation Crossroads took place in the Marshall Islands, with small fleets of derelict ships being the targets.
Operation Crossroads was the first detonation of nuclear weapons at sea, as well as the first nuclear weapons tests to be announced ahead of time. The tests occurred at on 1 July 1946 for Able, 25 July 1946 for Baker. A third test, Charlie, was planned, but subsequently canceled for undisclosed reasons.
Operation Crossroads was the first opportunity for scientists and military men to see the effects of a nuclear explosion at sea, and for many not present at the Trinity test, their first time observing a nuclear explosion in person. With the rivalry between the United States and the USSR increasing, many at the time believed nuclear weapons could be used in war again. The United States wanted a solid advantage, and to stay ahead in nuclear weapons technology.
Operation Crossroads included one aerial test (Able), where the bomb was detonated at an altitude of 520 feet (158 m), and a submarine test (Baker), occurring 90 feet (27 m) underwater. Baker was deployed by a landing ship that had been used during the invasion of Iwo Jima, LSM-60, which became the first ship to use a nuclear weapon. LSM-60 stayed in place during the explosion, and was completely vaporized.
The Able test sunk five ships: Sakawa, an Imperial Japanese Navy cruiser, USS Anderson, USS Lamson, USS Carlisle, USS Gilliam. Baker sunk seven ships: Nagato, an Imperial Japanese Navy battleship, USS Arkansas, USS Saratoga, USS Apogon, USS Pilotfish, USS LSM-60, and District Craft YO-160. Prinz Eugen survived both tests, but was so radioactive after the ordeal that repairing its leaks would have been impractical, and the ship was capsized at the nearby Kwajalein Atoll.