In late October 1945, members of the United States Navy's emerging Atomic Bomb Group (William Parsons, Frederick Ashworth, and Horatio Rivero) discussed the possibility of conducting nuclear tests to determine the effects of atomic detonations on naval ships. Four types of tests were put forward in what became known as Operation Crossroads: detonation of a device suspended by a blimp, a deep-water detonation, a shallow-water burst, and a high-altitude delivery by a B-29 bomber. The blimp test was quickly eliminated, while planning proceeded on the remaining three proposals. President Truman authorized the Crossroads Tests on January 10, 1946.
The Navy selected the remote atoll of Bikini in the Marshall Islands as the test site. Bikini had enough land area to support the operation as well as a large lagoon. The lagoon was of critical importance, since the Navy planned to assemble a vast array of captured German, Japanese, and obsolete American warships as targets for the weapons tests. The Bikini Islanders agreed to vacate the atoll for an unspecified period of time (they have yet to return) and allow the United States Government unrestricted use of the islands and lagoon.
Los Alamos scientists played the key role in Crossroads: "Arrangements for setting up the bomb, including assembly and transportation of components must be made through the organization which furnishes the bomb, namely the Manhattan Project and the Los Alamos Scientific Laboratory. Since the phenomena accompanying the release of energy of an atomic bomb are known to and have been successfully observed by the parties of the Los Alamos Laboratory, it would be unsafe, unworkable and infinitely confusing to have any other organization attempt to dominate the observations."
The first test, codenamed Able, was a high altitude drop of a Fat Man device on June 30, 1946. The bomb missed the aiming point by about a half mile and, as a result, sunk only five ships. Shot Baker, the second test, was a dramatic shallow-water burst sinking eight ships. More significantly, the sea water irradiated by Baker washed over the target fleet, rendering all ships uninhabitable. Because of the extensive damage and contamination caused by shot Baker and the very small stockpile of nuclear weapons, the planned deep-water test was cancelled.
As effects tests, Able and Baker demonstrated that atomic bombs could be used as tactical weapons and used against small targets.