From the start of the Trinity project in 1945 until the signing of the Limited Nuclear Test Ban Treaty in 1963, the United States conducted 19 operations (test series) involving tests of atmospheric nuclear weapons. In the course of these operations, more than 230 detonations (shots) were carried out, primarily at the Nevada Test Site and the Pacific Proving Ground. It is estimated that more than 200,000 Department of Defense (DoD) personnel, both military and civilian, participated in these tests.
The first test shot, dubbed Trinity by Robert Oppenheimer, was the most violent man–made explosion in history to that date. Detonated from a platform on top of a 100-foot high steel tower, the Trinity device used about 13½ pounds of plutonium. Los Alamos scientists discussed the possibility that the atmosphere might be ignited and the entire earth annihilated but dismissed this as extremely remote. On July 16, 1945, the Trinity device detonated over the New Mexico desert and released approximately 21 kilotons of explosive yield. The predawn blast, which temporarily blinded the nearest observers 10,000 yards away, created an orange and yellow fi reball about 2,000 feet in diameter from which emerged a narrow column that rose and fl attened into a mushroom shape.
If nuclear weapons were going to become a cornerstone of Cold War military strategy, military officials needed to know more about the effects produced by these weapons. Following the Trinity test and the bombings of Hiroshima and Nagasaki, officials still knew very little about weapon effects, especially on naval targets.
Operation Crossroads was conducted at Bikini Atoll in the Marshall Islands. Shot Able, a plutonium bomb dropped from a B–29 on July 1, performed as well as the two previous plutonium devices, at Trinity and Nagasaki. Able nonetheless failed to fulfill its pretest publicity buildup. Partly this was because expectations had been too extravagant and observers were so far from the test area that they could not see the target array. Partly it was because the drop had missed the anticipated ground zero by some distance.
Baker proved much more impressive. Detonated ninety feet underwater on the morning of July 25, Baker produced a spectacular display as it wreaked havoc on a seventy–four–vessel fl eet of empty ships and spewed thousands of tons of water into the air. As with Able, the test yielded explosions equivalent to 21,000 tons of TNT. Baker, helped restore respect for the power of the bomb. A planned third shot, to be detonated on the bottom of the lagoon, was canceled.
Responsibility for the planning and conduct of U.S. atmospheric nuclear weapons tests was shared by the DoD and the Atomic Energy Commission (AEC), the successor to the Manhattan Engineer District and the predecessor of the Nuclear Regulatory Commission. The AEC was responsible for the development of nuclear technology, whereas the DoD was responsible for incorporating this technology into the United States military defense program. DoD military personnel (Army, Navy, Air Force, and Marine Corps members), as well as civilian employees and contractors of the DoD and AEC, all participated in nuclear weapons tests. The types of personnel present and the nature of their involvement in these tests varied by shot and by series.
In general, the roles and functions of DoD personnel present at test detonations were to witness the nuclear weapon test event, to participate in military exercises and perform tactical functions or support services, and to set up various scientific experiments and collect post-shot data. Dose limits in place during the tests functioned as safety guidelines rather than as restrictive cut-points. These DoD-prescribed exposure limits varied, but generally allowed maximum exposures of 3 to 5 rem (30 to 50 millisievert [mSv]) “per test or series”.
The Defense Nuclear Agency estimates that the average dose received by a participant was about 6 mSv (DTRA, 1999)— approximately twice as large as the average annual natural background dose received by a person living in the United States and more than 16 times lower than the threshold for deterministic effects. It is estimated that less than 1 percent of all test participants received doses in excess of 50 mSv, the current annual dose limit for radiation workers.
Operation Sandstone would concentrate on bomb performance and the validation of three new weapon designs and not on weapon effects. The test series, conducted from April 15 to May 15, 1948, proved an overwhelming success. The three tests performed as expected and fallout remained largely localized. The second shot, Yoke, at forty–nine kilotons, provided the largest explosive yield yet achieved, over twice the size of the Trinity test. More importantly, the new bomb designs translated into more effi cient use of fissionable materials. From thirteen weapons in 1947, the nuclear stockpile increased to fifty in 1948.
The eastern coast of the United States offered suitable test sites where radioactivity would be harmlessly blown out to sea. Most ideal would be a site somewhere between Cape Hatteras and Cape Fear where “the population is not dense, meteorology is favorable during two–thirds of the year between 20% and 30% of the time, and the waters of the Gulf Stream will remove the waste products to the open Atlantic.
By January 1950, test planners envisioned a four–shot series, codenamed Greenhouse, to be conducted at Enewetak in spring 1951. Greenhouse would not involve the testing of a thermonuclear device. But two of the four planned tests would explore some of the principles of fusion. By November 1950, Los Alamos bomb designers realized that possible design fl aws existed in the implosion devices slated to be tested during the Greenhouse series. They concluded that several test detonations needed to be made, if at all possible, prior to Greenhouse, which became Ranger.
On 18 December 1950 President Truman approved the choice of the Frenchman Flat area in Nevada as the site for future nuclear testign in the Continenetal United States. On 11 January 1951, Truman officially approved the Ranger test series. Joseph Myler, a reporter for United Press, noted that the Nevada tests would be “special purpose” devices that were “more compact and more deliverable,” such as “atomic missile and atomic artillery warheads” or “an atomic mortar shell.” In the early dawn of January 27, 1951, Able, the first shot in the Ranger series, detonated on schedule and as planned. At one–kiloton yield, Able, the world’s tenth nuclear detonation, was much smaller than any prior shot. In a span of ten days, five tests were detonated at the Nevada Test Site, and then Ranger was over.
A few weeks after Ranger Ulam and Teller proposed a radically new and more promising approach for starting and sustaining a fusion reaction - staged radiation implosion. Greenhouse consisted of four tests. The first two — Dog and Easy — were weapon development tests. The third — George — used a large fission yield to ignite, for the first time, a small mass of thermonuclear fuel. With an overall yield of 225 kilotons, George was the most impressive and largest shot to date. The fourth shot — Item — provided the initial demonstration of a technique called “boosting” in which a fission device contained some thermonuclear fuel that enhanced the yield of the fission explosion.
The Atomic Energy Commission conducted Operation Buster-Jangle at the Nevada Test Site, which consisted of seven tests, in October-November 1951. The weapons-assembly work for Operations Buster-Jangle in 1951 utilized many of the basic techniques and systems employed during Operations Ranger and Greenhouse. After the exercise, the Congressional delegates issued a joint statement which stated that “Atomic bombs can be used on the battlefield to pave the way for ground advance without radiation hazard.”Tumbler-Snapper in April-June 1952 consisted of eight shots. The first three were air-dropped weapon effects tests designed to measure blast pressure, as well as ground shock and thermal radiation. The remaining five shots were Snapper weapon development tests.
Operation IVY was an atmospheric nuclear test series held in the Atomic Energy Commission’s (AEC) Pacific Proving Ground at Enewetak Atoll in the Marshall Islands from November 1 to December 31, 1952. The series consisted of the two detonations. The first thermonuclear device, code named Mike, detonated by the Commission at Enewetak, during Operation Ivy. The device exploded 01 November 1952 with a yield at 10.4 megatons.
Operations GREENHOUSE, UPSHOT-KNOTHOLE, CASTLE, REDWING, and PLUMBBOB represent a subset of the 19 total nuclear weapons test series. These five series included 62 shots and involved approximately 68,168 military participants. The subset of five series was selected by the Medical Follow-up Agency's Subcommittee on Exposure at Tests of Nuclear Weapons as the focus of the 1985 National Research Council report Mortality of Nuclear Weapons Test Participants. These particular series were chosen to include similar numbers of Nevada Test Site and Pacific Proving Ground participants. The availability and quality of both personnel and radiation dosimetry records were also considered in the selection of series for study. Three of the five series were noted in the 1985 National Research Council report as including shots in which unexpected potential for radiation exposure arose during the test event.
The CASTLE series was conducted to test large-yield thermonuclear devices. Operation CASTLE took place at the Pacific Proving Ground in March through May of 1954 and consisted of six test detonations, ranging in magnitude from 110 kt to 15 megatons (Mt). Shot BRAVO, the first detonation, significantly exceeded its expected yield and “was the largest device ever detonated by the U.S. Government as part of atmospheric nuclear weapons testing” (Gladeck and Johnson, 1996). Unexpectedly heavy fallout affected a small number of U.S. military personnel and the Japanese fishing boat Fortunate Dragon No.5. Shot BRAVO was without question the worst single incident of fallout exposures in all the U.S. atmospheric testing program”. No other test in the series resulted in significant unexpected exposures.
REDWING was a 17-detonation nuclear weapons test series conducted at the Pacific Proving Ground in the spring and summer of 1956. Like those in the CASTLE series, these detonations were conducted primarily as tests of thermonuclear devices. REDWING tests included six barge shots, three surface shots, six tower shots, and two air drops, ranging in magnitude from 13.7 kt to 5 Mt.
Because of the complications associated with Shot BRAVO in the CASTLE series, additional safety precautions were taken, and dosimeters were issued to all participants in Operation REDWING. This operation ran smoothly except for two incidents. One of the airdrops, Shot CHEROKEE, detonated considerably off target although no unexpected radiation exposures occurred as a result. Shot TEWA, fired at Bikini Atoll, resulted in fallout on the Enewetak base camp. Personnel remaining in the camp at the time of the test were unexpectedly exposed to ionizing radiation.
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