CROSSROADS was a two-shot atmospheric nuclear test series conducted at Bikini Atoll during July and August 1946. The first test (Shot ABLE) was a device dropped on 1 July 1946 from an aircraft and exploded at an altitude of 520 feet over an array of target ships. The second test (Shot BAKER) was detonated on 25 July 1946, 90 feet below the water's surface amongst an array of target ships.
Two hundred forty-two ships participated in Operation CROSSROADS. Over 39,300 U.S. Navy personnel have been identified as having participated in the operation. The ships that participated can be divided into three categories: support ships, remanned target ships and unremanned target ships. Support ships were present at the test site at some time during the operational period, but were not in the target area at the time of the shots. Remanned target ships were ships that were present in the target area at the time of the shots. The crews for these ships were evacuated to support ships at the time of the detonations. The damage and contamination of these ships was such that it was determined they could be remanned by their crews after the detonations. The third category of ships, unremanned target ships, were also present in the target area at the time of the detonations. However, their crews, which had been evacuated to support ships, could not permanently return to their home ships because the ships had either sunk or were too severely damaged or contaminated to be remanned. Most of the crews of the unremanned target ships were shipped as passengers back to Kwajalein, Pearl Harbor and California west coast ports. About 10% of the crews for the unremanned target ships were assigned as replacement crewmembers of support ships. The three categories of ships included many types such as battleships, cruisers, destroyers, oilers, troop transports, aircraft carriers, submarines, patrol, supply, salvage, yard and utility ships.
The Operational Area for this data collection effort is defined as Bikini Atoll. The Operational Period is defined as 1 July 1946 through 31 August 1946. All service members who were present in the Operational Area for any time during the Operational Period qualify for participation. Some personnel at Kwajalein and Enewetak also qualify as participants because they were at those locations to support the operation. The Post Operational Period for CROSSROADS extends from 1 September 1946 through 28 February 1947.