Operation GREENHOUSE

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 at 800-462-3683.

Operation GREENHOUSE, the third series of nuclear weapons tests in the Marshall Islands in the Pacific 

Ocean, was conducted by the Atomic Energy Commission (AEC) from April 8 to June 20, 1951. The series 

consisted of four nuclear weapons tests, all tower shots and all nuclear fission devices except as noted below. 

All tests were conducted on Enewetak Atoll.

GREENHOUSE was the first test operation in the Pacific since the Soviet Union surprised the world with its 

first nuclear detonation in 1949, which was much sooner than American scientists had expected. This spurred 

the United States in an all-out effort to stay ahead of the Soviet Union by developing the much more powerful 

hydrogen bomb, a thermonuclear device that derived its explosive energy from the fusion of hydrogen atoms. 

Although no complete fusion devices were tested at GREENHOUSE, the operation helped proof-test the 

thermonuclear triggering process through achieving a detectable fusion component of nuclear yield, an 

important step toward the first successful thermonuclear detonation at Operation IVY the next year. 

Thermonuclear processes also contributed to a design successfully tested at GREENHOUSE to boost the 

efficiency of fission explosions.

In addition to the weapons development experiments, the Department of Defense (DOD) conducted tests of 

the physical and biological effects of nuclear weapons—tests that involved a large number of DOD

organizations and personnel and considerable onsite construction.

The joint military and civilian organization that conducted Operation GREENHOUSE was called Joint Task 

Force 3 (JTF 3). JTF 3 coordinated and controlled the efforts of all military units, civilian government 

employees, and civilian DOD and AEC contractors. About 10,500 DOD personnel participated.

Summary of Operation GREENHOUSE Nuclear Weapons Testsa

Shot Local Date (1951) Location Burst Type/Height Yieldb

DOG April 8 Runit Island Tower (300 feet) 81 kilotons

EASY April 21 Enjebi Island Tower (300 feet) 47 kilotons

GEORGE May 9 Eleleron Island Tower (200 feet) 225 kilotons

ITEM May 25 Enjebi Island Tower (200 feet) 45.5 kilotons

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.
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Operation GREENHOUSE Highlights

Operation GREENHOUSE proceeded as planned except for the fallout that occurred on the residence islands 

after each shot except GEORGE. The fallout from Shot DOG was heavier than previously had been 

encountered in a residence situation at a nuclear test site; this was the first time that fallout appreciably 

increased cumulative doses of support personnel relative to the dose limit. The fallout on residence islands 

from Shot ITEM was heavier yet.

Fallout from Shot DOG, caught in wind shifts in the hours after detonation, doubled back on the atoll and 

contaminated some of the islands and ships. Of the residence islands, Parry Island received the most with a 

peak reading (an average from several points around the island during the hours of highest radiation from 

accumulated fallout) of 0.083 roentgen per hour (R/h). High radiation levels on the forward islands postponed 

all but the most essential survey and recovery missions until the next day, when the radiation had decayed to 

acceptable levels.

Only very light fallout from Shot EASY, compared to the fallout from Shot DOG, fell on the residence islands. 

JTF planners situated Shot EASY on Enjebi, the largest of the forward islands, to accommodate extensive 

DOD projects. Because of these projects, more DOD personnel were involved in the forward activities at Shot 

EASY than for any of the other three shots. Most of the activity involved an extensive DOD structural response 

program in which a large number of full-sized and scaled-down dummy structures were built at varying 

distances from the shot point. The structures, sample buildings and aircraft parts, were heavily instrumented 

to record their response to the nuclear burst. Also, DOD conducted the largest biotic test program of the 

Oceanic tests; this program used a variety of plant specimens, as well as mice, pigs, dogs, and other animals.

Shot GEORGE, at 225 kilotons, nearly tripled the yield of any nuclear device detonated up to that time. 

Because of the large anticipated yield, the winds had to be consistently from the south before detonating to 

assure that fallout would blow away from occupied atolls. With the help of a nearby typhoon, the wind 

conditions were perfect, with strong southerly winds at all altitudes. No fallout was detected at the residence 

islands.

Shot ITEM, the last shot of GREENHOUSE, was moved up 3 hours to avoid unfavorable winds predicted for 

later in the morning. Even so, high-altitude winds blew fallout back onto the residence islands and ships at 

anchorage in the lagoon. The first wave of fallout began in the morning, 3 to 4 hours after the detonation, and 

the second wave peaked in the early evening. The peak reading in occupied areas was 0.118 R/h on 

Enewetak Island, which received the most fallout. The men living on the residence islands were exposed to 

fallout there until they departed from the atoll.

The amount of fallout received by the six JTF 3 ships varied with their locations at shot time and their 

decontamination procedures. Radiation intensities were lower for shipboard personnel than for island-based 

personnel because many of the ships' external surfaces could be decontaminated quickly by the water 

washdown systems.

An important experimental program at GREENHOUSE was the use of unmanned, radio-controlled drone 

aircraft for cloud sampling. Eight B-17 drones were flown close to the detonation to measure blast and thermal 

effects and then into the nuclear cloud to collect radioactive samples.

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.
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Standards governing permissible radiation dose were established as upper limits for each individual. The 

standards, which followed those set by the National Committee on Radiation Protection, were 0.1 rem∗ per 

day, not to exceed a total of 3.9 rem for 13 weeks. The Commander of JTF 3 could authorize a total dose of 

up to 3.0 rem on any one day for personnel who had to perform special missions, but only once per individual.

Of the approximately 10,500 military and DOD civilians in the test area during the operation, about 2,300 were 

badged one or more times. Film badges were issued to individuals who had the potential to be exposed to 

radiation while performing their duties, such as radiation monitors, boat pool crews, aircrews, runway crash 

crews, personnel responsible for decontaminating aircraft, and especially those visiting any of the forward 

islands shortly after the shots. Film badges for personnel entering radioactive areas normally were issued and 

turned in daily. Boat pool and ship badges generally were issued for one week. For each test, more than 

75 film badges were distributed to each of the six participating JTF 3 ships to be worn for 7 days after the test 

by representatives of cohort groups (participants physically grouped together and engaged in similar activities). 

The dose to these individuals would approximate that of the whole group. After being turned in, the badges 

were developed and the reading recorded on 5x8-inch dose cards maintained for each individual who was 

badged. Dose cards were not maintained for unbadged personnel.

Radiation Doses at Operation GREENHOUSE

A number of individuals had recorded film badge readings of between 5 and 9 rem. The higher doses among 

DOD participants were recorded for radiation monitors with the radiological safety unit, individuals supporting 

scientific projects, and Air Force personnel working in the sampling program and long-range radioactive cloudtracking programs, especially the Air Force Experimental Aircraft Unit. This unit controlled the B-17s used as 

drones and decontaminated personnel and aircraft on Enewetak Island.

Fallout from Shots DOG, EASY, and ITEM on the residence islands and on the ships contributed to the 

accumulated dose of everyone who lived there. For typical support personnel remaining on the islands 

throughout the operation, reconstructed doses from DOG fallout range from 0.6 to 1.3 rem; doses for 

personnel on ships tend to be lower because of the washdown systems and because sailors spent a large 

amount of time below deck. The fallout from ITEM was most intense. The corresponding reconstructed doses 

from ITEM through 4 days after the shot, when many participants departed, range from 1.1 to 2.1 rem. Most 

people had left Enewetak Atoll within a week after Shot ITEM, but some garrison forces remained for months 

thereafter and received greater doses.

Many of these personnel were not issued film badges. Others were issued film badges for a short time only –

to help out briefly on a mission, for example – but went unbadged for the balance of the time. At the 

conclusion of GREENHOUSE, doses for some of these men were estimated using erroneous assumptions and 

entered onto their individual dose cards. For example, readings on Parry Island were used regardless of the 

residence islands on which a person was based and without consideration of actual lengths of stay on the 

islands. Most of these estimates were either understated or overstated when compared to the actual radiation 

exposures. Some personnel who were almost certainly exposed to fallout had no dose entered in their 

personal files.

 ∗ 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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To correct these inadequacies, doses in the files for individuals who did not continuously wear a film badge 

have been replaced by dose reconstructions derived by the NTPR Program from the known radiation 

conditions of each island and ship.

Reconstructed doses for typical shipboard and land-based personnel are derived and published in “Analysis of 

Radiation Exposure for Naval Personnel at Operation GREENHOUSE” (DNA-TR-82-15). The dose totals for 

GREENHOUSE participants are depicted below.

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

Personnel at Operation GREENHOUSE” (DNA-TR-82-15). Also see the report “Operation GREENHOUSE 

1951” (DNA 6034F). These reports are available online at 

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

September 2021