Operation Crossroads (1946) in 1946 was an underwater shot. The first use of the Pacific Proving Grounds was during
Operation Crossroads, the first nuclear testing done after the
atomic bombing of Hiroshima and Nagasaki. Two fission bombs, both with a yield of 21 kilotons, were
tested at
Bikini Atoll. "Able" was detonated at an altitude of 520 ft (158 m) on July 1, 1946, and "Baker" was detonated at a depth of 90 ft (27 m) underwater on July 25. Both tests used a flotilla of obsolete vessels from
World War II with the intent of learning the effects of nuclear weapons on naval fleets. The "Baker" shot created a large condensation cloud and spread much more
radioactive water onto the ships than was expected; many of the surviving ships became too "hot" to be used or decontaminated and eventually had to be sunk.
Operation Sandstone (1948) Three weapons were detonated on the
Enewetak Atoll as part of
Operation Sandstone in 1948.
Operation Greenhouse (1951) Four weapons were detonated on the Enewetak Atoll as part of
Operation Greenhouse in 1951. Two are of particular note: Greenhouse "Item" was the first use of a
boosted fission weapon, and "George" was a
thermonuclear experiment designed to prove the feasibility of the
Teller-Ulam design for the possibility of developing
hydrogen bombs.
Operation Ivy (1952) shot, only a large crater (at left) remained of the island of
Elugelab. Two weapons were detonated at the Enewetak Atoll as part of
Operation Ivy in 1952. One of them,
Ivy King, was the largest pure-fission bomb ever detonated, with a yield of 500
kilotons, and the other,
Ivy Mike, was the first hydrogen bomb device (it was too large to be an actual weapon), with a yield of 10.4
Mt.
Operation Castle (1954) test of 1954 spread
nuclear fallout across the
Marshall Islands, parts of which were still inhabited. Six very large nuclear tests were conducted at the
Bikini Atoll and the Enewetak Atoll as part of
Operation Castle in 1954. The most notable was
Castle Bravo, which was the first deployable (dry fuel) hydrogen bomb developed by the United States. Its yield, at 15 Mt, was over twice as powerful as was predicted, and remains the largest weapon ever detonated by the United States. It spread
nuclear fallout over a wide area, including the Enewetak Atoll,
Rongerik Atoll,
Ailinginae Atoll, and
Rongelap Atoll. The U.S. Navy evacuated the islanders within the next few days, but many of the natives were exposed to radiation prior to evacuation. The fishermen aboard the Japanese fishing vessel
Daigo Fukuryu Maru were also exposed, and one man died soon after from complications of
radiation sickness, resulting in considerable international controversy.
Operation Redwing (1956) Seventeen nuclear weapons were detonated on the Bikini and Enewetak Atolls as part of
Operation Redwing in 1956. Many of them were designed to prove the feasibility of numerous
thermonuclear weapon designs, with yields ranging from around 2 to 5 Mt.
Operation Hardtack I (1958) Thirty-five weapons were detonated at the Bikini Atoll, Enewetak Atoll, and
Johnston Island as part of
Operation Hardtack I in 1958.
Operation Dominic (1962) Thirty-six weapons were detonated at sites in the Pacific Ocean in the vicinity of
Christmas Island and
Johnston Atoll as part of
Operation Dominic I. Though these tests were not conducted in the Marshall Islands, they are officially considered part of the Pacific Proving Grounds. The portion of the Dominic series of tests that were
high altitude nuclear explosions were known as
Operation Fishbowl, though not all were successful (one detonated on launchpad and resulted in a substantial
plutonium contamination). Two of the tests were of operational weapons systems—the
ASROC anti-submarine rocket and the
Polaris SLBM (the latter test, Frigate Bird, was the only operational submarine-launched ballistic missile test with a live warhead ever undertaken by the USA). ==Partial Test Ban Treaty ==