Operation CASTLE

Note: For information related to claims, call the Department of Veterans Affairs (VA) at 800-827-1000 or the 

Department of Justice (DOJ) at 800-729-7327. For all other information, call the Nuclear Test Personnel 

Review (NTPR) Program Helpline at 800-462-3683.

Operation CASTLE was a six-detonation nuclear weapon test series (see table) held at the Atomic Energy 

Commission’s (AEC) Pacific Proving Ground (PPG) from March 1 to May 31, 1954. The PPG consisted 

principally of Enewetak and Bikini Atolls in the northwestern Marshall Islands in the Central Pacific Ocean.

Historical Background

The CASTLE series was held to test large-yield thermonuclear, or hydrogen, devices. Work on this class of 

devices had progressed through the GREENHOUSE-GEORGE demonstration shot in 1951 and the IVY-MIKE 

shot of 1952. MIKE was the first device that generated substantial explosive energy from the fusion, or joining, 

of hydrogen atoms. These explosive devices were developed by the AEC, the civilian agency authorized to 

perform this activity by the Atomic Energy Act of 1946.

The devices were tested at the PPG by a joint military and civilian organization designated as Joint Task 

Force 7 (JTF 7). This was a military organization in form, but was populated by military, civil service, and 

contractor personnel of the Department of Defense (DOD) and AEC. The commander of this force was the 

appointed representative of the AEC and reported also to the Joint Chiefs of Staff and the Commander-inChief, Pacific. The peak DOD numerical strength of CASTLE was approximately 17,300 personnel.

Numerous technical demonstrations were carried out in conjunction with each of the six detonations. These 

demonstrations measured the power and efficiency of the devices and attempted to gauge the military effects 

of the explosions. DOD personnel participated in this test operation as individuals whose duty stations were at 

the AEC design laboratories, as units performing separate demonstrations, and as units performing various 

support roles. The CASTLE operations placed almost all of the Navy support groups at Bikini, where its ships 

provided living space for personnel who were evacuated from the islands for the first test and then could not 

return to live there because of the potential radiation exposure.
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Summary of Operation CASTLE Nuclear Weapons Tests (1954)a

Local Date 

(1954) Shot Location Yieldb

Mar 1 BRAVO Bikini; sandspit off Nam Island 15 megatons

Mar 27 ROMEO Bikini; barge in BRAVO crater 11 megatons

Apr 7 KOON Bikini; surface of Eneman Island 110 kilotons

Apr 26 UNION Bikini; barge in lagoon off Iroij Island 6.9 megatons

May 5 YANKEE Bikini; barge in UNION crater 13.5 megatons

May 14 NECTAR Enewetak; barge in MIKEc crater 1.69 megatons

a Source: United States Nuclear Tests, July 1945 through September 1992, DOE/NV-209 (Rev. 15), Dec 2000. 

b One kiloton equals the approximate energy release of one thousand tons of TNT; one megaton equals the approximate 

energy release of one million tons of TNT.

c IVY series detonation in 1952.

Radiation Protection Standards

Safety standards were established to limit the exposure of participants to the effects of nuclear detonations 

while, at the same time, allowing them to receive the sometimes unavoidable small doses of radiation as they 

performed their missions in the radiation areas.

The standards, which followed those set by the National Committee on Radiation Protection, included a total 

dose not to exceed 3.9 rem∗ for 13 consecutive weeks. The Commander of JTF 7 could authorize a one-time 

dose up to 20 rem for certain air missions. 

Some key personnel approached or exceeded the CASTLE dose limit of 3.9 rem from being exposed to 

BRAVO fallout on Navy ships and from working in contaminated areas on Bikini. To allow for the completion of 

the remaining CASTLE shots, the JTF 7 commander issued a number of waivers authorizing doses of as much 

as 7.8 rem over 13 consecutive weeks. In a limited number of cases, even this level was exceeded.

Radiation Doses at Operation CASTLE

A limited number of JTF 7 personnel received radiation doses considerably in excess of the established limit. 

In particular, the 28 Army and Air Force personnel stationed on Rongerik Atoll had film badge readings of 32 to 

52 rem. Three members of the U.S. Navy Bikini Boat Pool had heavily exposed badges with readings from 85 

to 96 rem.

As a result of BRAVO, 21 individuals on USS PHILIP (DDE 498) and 16 on USS BAIROKO (CVE 115) 

sustained small skin lesions that resembled burns while at stations on the weather deck or near ventilation 

blowers. Initially these burns were deemed to be from beta radiation, but later they appeared to have been 

lime burns from chemical reactions with coral in the fallout.

 ∗ A rem is a radiation protection unit of measure that quantifies the risk of biological effects resulting from exposure to 

ionizing radiation. Ionizing radiation is any radiation (gamma, x-ray, beta, neutron, or alpha) capable of displacing 

electrons from atoms or molecules, thereby producing ions. According to the National Council on Radiation Protection 

and Measurements (NCRP, Report No. 160, Table 1.1), the general U.S. population receives about 0.62 rem per year 

from natural background radiation sources (radon, cosmic rays, and rocks) and man-made radiation sources (medical 

diagnostic x-rays and consumer products). As a basis of comparison, a standard diagnostic chest x-ray delivers a 

radiation dose of about 0.02 rem.
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The reconstructed dose to the crew of USS PATAPSCO (AOG 1) is 4.7 rem for the period from the time fallout 

commenced to their disembarking at Pearl Harbor. USS PATAPSCO, a Navy gasoline tanker, was 

approximately 190 nautical miles east of Bikini and steaming toward Hawaii when it was caught in the main 

path of the BRAVO fallout.

The totals of reconstructed and film badge doses for CASTLE participants are depicted below. 

Figure 1. Doses accrued by CASTLE personnel

For more information on reconstructed doses, see the reports “Analysis of Radiation Exposure for Naval 

Personnel at Operation CASTLE” (DNA-TR-84-6), “Analysis of Radiation Exposure for Additional Naval 

Personnel at Operation CASTLE – Supplemental Report” (DNA-TR-89-256), and “Analysis of Radiation 

Exposure – Service Personnel on Rongerik Atoll” (DNA-TR-86-120). Also see the report “CASTLE Series 

1954” (DNA 6035F). These reports are available online at 

https://www.dtra.mil/DTRA-Mission/Reference-Documents/NTPR-Info/.

September 2021