4
Description of Operation CROSSROADS

The Defense Nuclear Agency (DNA) has produced detailed documents about each nuclear test series. DNA Report 6032F (1984) describes activities during Operation CROSSROADS, including primary documents such as ship logs. DNA's public affairs office issued a two-page fact sheet on CROSSROADS, dated 5 April 1984, from which the following description draws heavily.

In July 1946, the U.S. military conducted Operation CROSSROADS to determine, in a controlled way, ''the effects of nuclear weapons on ships, equipment, and material." This first nuclear weapon test series at the Pacific Proving Grounds consisted of two detonations, ABLE (detonated at an altitude of 520 feet) and BAKER (detonated 90 feet under water), each with a yield of approximately 23 kilotons. 8

More than 90 vessels were positioned as the target fleet, while approximately 150 other ships were used to transport and house personnel and accommodate technical stations, such as laboratories and workshops. Approximately 42,000 men9 participated on site at some time during the CROSSROADS official operational period (1 July through 31 August 1946).

8  

 The Hiroshima bomb was 15 kilotons.

9  

 Consonant with military practice in the 1940s, there were not many women involved in naval ship-based operations. DNA data indicate a few women (perhaps 25) on board. We include them in analyses but have chosen to use male comparison mortality rates.



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--> 4 Description of Operation CROSSROADS The Defense Nuclear Agency (DNA) has produced detailed documents about each nuclear test series. DNA Report 6032F (1984) describes activities during Operation CROSSROADS, including primary documents such as ship logs. DNA's public affairs office issued a two-page fact sheet on CROSSROADS, dated 5 April 1984, from which the following description draws heavily. In July 1946, the U.S. military conducted Operation CROSSROADS to determine, in a controlled way, ''the effects of nuclear weapons on ships, equipment, and material." This first nuclear weapon test series at the Pacific Proving Grounds consisted of two detonations, ABLE (detonated at an altitude of 520 feet) and BAKER (detonated 90 feet under water), each with a yield of approximately 23 kilotons. 8 More than 90 vessels were positioned as the target fleet, while approximately 150 other ships were used to transport and house personnel and accommodate technical stations, such as laboratories and workshops. Approximately 42,000 men9 participated on site at some time during the CROSSROADS official operational period (1 July through 31 August 1946). 8    The Hiroshima bomb was 15 kilotons. 9    Consonant with military practice in the 1940s, there were not many women involved in naval ship-based operations. DNA data indicate a few women (perhaps 25) on board. We include them in analyses but have chosen to use male comparison mortality rates.

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--> Before each detonation, all participants were evacuated from target vessels and the Bikini Atoll to locations at least 10 nautical miles away. Shot ABLE was released from the air on 1 July 1946, detonating about 1750 feet off target and sinking five ships. Most surviving target ships were reboarded within 24 hours. Activities in preparation for BAKER, including vessel inspection, instrument recovery, and remooring, continued on schedule. On 25 July 1946, the detonation of BAKER created such pressure under water that huge splashes from the bottom of the lagoon sprayed radioactive water and debris over most of the target fleet. This limited the possible activities on target ships, such as physical inspections or pickup of the recorder and measurement devices. In early August, efforts began to decontaminate the fleet by intensive washing of ship surfaces; all boarding parties were accompanied by radiological monitors, who were responsible for identifying and limiting exposure to radiation. DNA describes radiological supervision in its fact sheet (1984): All CROSSROADS operations were undertaken under radiological supervision intended to keep personnel from being exposed to more than 0.1 roentgen per day. At the time, this was considered to be an amount of radiation that could be tolerated for long periods without any harmful effects on health. Radiological supervision included predicting areas of possible danger, providing trained personnel equipped with radiation survey instruments to act as guides during operations involving potential exposure, and elaboration of rules and regulations governing conduct in these operations. Personnel were removed for one or more days from areas and activities of possible exposure if their badges showed more than 0.1 R/day exposure About 15 percent of the JTF 1 personnel was issued at least one of the 18,875 film-badge dosimeters during CROSSROADS. Approximately 6,596 personnel were on islands or ships that had no potential for radiation exposure. Personnel anticipated to be at greatest radiological risk were badged, and a percentage of each group working in less contaminated areas was badged. The maximum accumulated exposure recorded (was 3.72 R received by) a radiation safety monitor[ing person]. This report discusses radiation measurement and dosimetry at length in Chapter 8. Support ships were soon registering contamination, arising from radioactive marine growth on hulls and radioactive water being piped through ships' systems. Between 10 August and the end of September 1946, target ships were towed to Kwajalein Atoll, where the water was uncontaminated, for ammunition off-loading and further work. Most target vessels were eventually sunk in the area, but 12 ships were reboarded by their crews and sailed to the U.S., and others were towed to the U.S. and Hawaii for radiological inspection. Before returning to the fleet,

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--> support ships had to receive radiological clearance; if necessary, they underwent decontamination. DNA designates the period 1 July through 31 August 1946 as Operation CROSSROADS, adding the 6-month period 1 September 1946 through 28 February 1947 as the ''post-CROSSROADS" period. The period after that, however, despite ongoing work in Navy yards and in the atoll on contaminated ships, is officially considered neither the CROSSROADS nor post-CROSSROADS period.