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The "Smoky" shot of Operation Plumbbob
The 43,000 foot high cloud as seen from the control point, 30 minutes after the Priscilla event

Operation Plumbbob was a series of nuclear tests conducted between May 28 and October 7, 1957, at the Nevada Test Sitemarker, following Operation Redwing, and preceding Operation Hardtack I. It was the biggest, longest, and most controversial test series in the continental United Statesmarker.


The operation was the sixth test series and consisted of 29 explosions, of which two did not produce any nuclear yield. 21 laboratories and government agencies were involved. While most Operation Plumbbob tests contributed to the development of warheads for intercontinental and intermediate range missiles, they also tested air defense and anti-submarine warheads with small yields. They included 43 military effects tests on civil and military structures, radiation and bio-medical studies, and aircraft structural tests. Operation Plumbbob had the tallest tower tests to date in the U.S. nuclear testing program, as well as high-altitude balloon tests. One nuclear test involved the largest troop maneuver ever associated with U.S. nuclear testing.

Almost 1,200 pigs were subjected to bio-medical experiments and blast-effects studies during Operation Plumbbob. On shot Priscilla (37 KT), 719 pigs were used in various different experiments on Frenchman Flat. Some pigs were placed in elevated cages and provided with suits made of different materials, to test which materials provided best protection from the thermal pulse. Other pigs were placed in pens at measuring distances from the epicenter behind large sheets of glass to test the effects of flying debris on living targets.

Approximately 18,000 members of the U.S. Air Force, Army, Navy and Marines participated in exercises Desert Rock VII and VIII during Operation Plumbbob. The military was interested in knowing how the average foot-soldier would stand up, physically and psychologically, to the rigors of the tactical nuclear battlefield.

Studies were conducted of radiation contamination and fallout from a simulated accidental detonation of a weapon; and projects concerning earth motion, blast loading and neutron output were carried out.

Nuclear weapons safety experiments were conducted to study the possibility of a nuclear weapon detonation during an accident. On July 26 1957, a safety experiment, "Pascal-A" was detonated in an unstemmed hole at NTS, becoming the first underground shaft nuclear test. The knowledge gained here would provide data to prevent nuclear yields in case of accidential detonations, for example a plane crash.

The Rainier shot, conducted September 19 1957, was the first fully contained underground nuclear test, meaning that no fission products were vented into the atmosphere. This test of 1.7 kilotons could be detected around the world by seismologists using ordinary seismic instruments. The Rainier test became the prototype for larger and more powerful underground tests.

Radiological effects

Plumbbob released 58,300 kilocuries (2.16 EBq) of radioiodine (I-131) into the atmosphere. This produced total civilian radiation exposures amounting to 120 million person-rads of thyroid tissue exposure (about 32% of all exposure due to continental nuclear tests). Statistically speaking, this level of exposure would be expected to eventually cause about 38,000 cases of thyroid cancer, leading to some 1,900 deaths. No hard data is available on the long-term civilian effects of these tests.

In addition to civilian exposure, troop exercises conducted near the ground near shot "Smoky" exposed over three thousand servicemen to relatively high levels of radiation. A survey of these servicemen in 1980 found significantly elevated rates of leukemia: ten cases, instead of the baseline expected four.

The first nuclear-propelled manmade object in space?

During the Pascal-B nuclear test, a heavy (900 kg) steel plate cap (a piece of armor plate) was blasted off the top of a test shaft at an unknown speed. The test's experimental designer Dr. Brownlee had performed a highly approximate calculation that suggested that the nuclear explosion, combined with the specific design of the shaft, would accelerate the plate to six times escape velocity. The plate was never found, but Dr. Brownlee believes that the plate never left the atmosphere (it may even have been vaporized by compression heating of the atmosphere due to its high speed). The calculated velocity was sufficiently interesting that the crew trained a high-speed camera on the plate, which unfortunately only appeared in one frame, but this nevertheless gave a very high lower bound for the speed. After the event, Dr. Robert R. Brownlee described the best estimate of the cover's speed from the photographic evidence as "going like a bat!!"

This incident was reputedly used as part of the technical justification for the Orion project for possible use of nuclear blasts for outer-space propulsion.

List of tests

The tests comprising Operation Plumbbob were as follows in TNT equivalent:
Operation Plumbbob Test Blasts
Test Name Date Yield Note
Boltzmann 1957-05-28 12 kt Tower shot
Franklin 1957-06-02 140 tons Fizzled
Lassen 5 June 1957 0.5 kt Balloon shot
Wilson 18 June 1957 10 kt Balloon shot
Priscilla 24 June 1957 37 kt Balloon shot
Coulomb-A 1 July 1957 zero yield Safety experiment
Hood 5 July 1957 74 kt Balloon shot, largest atmospheric test in the continental United Statesmarker
Diablo 15 July 1957 17 kt Tower shot
John 19 July 1957 2 kt Live fire of AIR-2 Genie air-to-air rocket
Kepler 24 July 1957 10 kt Tower shot
Owens 25 July 1957 9.7 kt Balloon shot
Pascal-A 26 July 1957 Slight Shaft safety experiment
Stokes 7 August 1957 19 kt Balloon
Saturn 10 August 1957 Zero yield Shaft safety experiment
Shasta 18 August 1957 17 kt Tower shot
Doppler 23 August 1957 11 kt Balloon shot
Pascal-B 27 August 1957 Slight Shaft safety experiment
Franklin Prime 30 August 1957 4.7 kt Balloon
Smoky 31 August 1957 44 kt Tower shot
Galileo 2 September 1957 11 kt Tower shot
Wheeler 6 September 1957 197 tons Balloon shot
Coulomb-B 6 September 1957 300 tons Surface safety experiment
Laplace 8 September 1957 1 kt Balloon shot
Fizeau 14 September 1957 11 kt Tower shot
Newton 16 September 1957 12 kt Balloon shot
Rainier 19 September 1957 1.7 kt Tunnel shot. First US underground nuclear test.
Whitney 23 September 1957 19 kt Tower shot
Charleston 28 September 1957 12 kt Balloon shot
Morgan 7 October 1957 8 kt Balloon Shot


  • Original source for test information.
  • Plumbbob page on the Nuclear Weapons Archive (also refers to manhole cover issue mentioned above).


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