Operation Plumbbob

Operation Plumbbob
Operation Plumbbob - Priscilla 2.jpg
Plumbbob Priscilla
Country United States
Test site Nevada Test Site
Period April - October 1957
Number of tests 30
Test type Atmospheric
Device type Fission/Thermonuclear
Max. yield 74 kt
Previous test Project 57
Next test Project 58

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



The operation was the sixth test series and consisted of 29 explosions, of which only two did not produce any nuclear yield. Twenty-one 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 smaller yields. They included forty-three 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 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. As shown and reported in the PBS documentary Dark Circle, the pigs survived, but with third-degree burns to 80% of their bodies.[1] Other pigs were placed in pens behind large sheets of glass at measured distances from the hypocenter 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 accidental 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 KT 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 between 11,000 and 212,000 excess cases of thyroid cancer, leading to between 1,000 and 20,000 deaths.[2]

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.[citation needed]

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. Before the test, 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.[3] 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!"[4][5] The use of a subterranean shaft and nuclear device to propel an object to escape velocity has since been termed a "thunder well".

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.

Objects can only be propelled to very high velocities by a nuclear explosion if they are located close to the burst point. Once a nuclear fireball has grown to a radius that is similar in size to the radius of a quantity of high explosive of similar yield, its energy density is about the same and very high velocities would not be produced. This radius for a 300 ton explosion is 3.5 meters.

The steel plate at the top of the shaft was over 150 m from the nuclear device, much too far for it to be propelled to extreme velocity directly by the explosion. The feature of Pascal-B that made this possible was the placement of the collimator close to the device. The mass of the collimator cylinder was at least 2 tonnes (if solid) and would have been vaporized by the explosion, turning it into a mass of superheated gas that expanded and accelerated up the shaft, turning it into a giant gun. It was the hypersonic expanding column of vaporized concrete striking the cover plate that propelled it off the shaft at high velocity.

To illustrate the physics, and estimate how fast it might have been going, consider that if the collimator absorbed a substantial part of the explosion energy (say a third of it, or 100 tons) it would have been heated to temperatures far higher than any conventional explosive (by a factor of 50 with the previous assumption).

The maximum velocity achieved by an expanding gas is determined by the equation:

    u = 2c/(gamma - 1)

where u is the final velocity, c is the speed of sound in the gas, and gamma is the specific heat ratio of the gas. If we further assume that the thermodynamic properties of vaporized concrete are similar to the hot combustion gases of high explosives, then the speed of sound in the vaporized collimator would be about 7 km/sec (the square root of 50 times the value of c for an explosive combustion gases, which is 1 km/sec). For molecular gases gamma is usually in the range of 1.1 to 1.5, for explosives it is 1.25. Thus we get:

    u = 2*7 km/sec / (1.25 - 1) = 56 km/sec

This is about five times Earth's 11.2 km/sec escape velocity, quite close to the figure of six times arrived at by Dr. Brownlee in his detailed computations. But the assumption that it might have escaped from Earth is implausible (Dr. Brownlee's discretion in making a priority claim is well advised). Leaving aside whether such an extremely hypersonic unaerodynamic object could even survive passage through the lower atmosphere, it appears impossible for it to retain much of its initial velocity while passing through the atmosphere. A ground launched hypersonic projectile has the same problem with maintaining its velocity that an incoming meteor has. According to the American Meteor Society Fireball and Meteor FAQ meteors weighing less than 8 tonnes retain none of their cosmic velocity when passing through the atmosphere, they simply end up as a falling rock. Only objects weighing many times this mass retain a significant fraction of their velocity.

The fact that the projectile was not found of course is no proof of a successful space launch. The cylinder and cover plate of Pascal-A was also not found, even though no hypersonic projectile was involved. Even speeds typical of ordinary artillery shells can send an object many kilometers, beyond the area of any reasonable search effort.

List of test blasts

Test Name Date Yield Note Image
Boltzmann 01957-05-2828 May 1957 12 kt Tower shot Operation Plumbbob - Boltzmann.jpg
Franklin 01957-06-022 June 1957 140 tons Fizzled Plumbbob Franklin 001.jpg
Lassen 01957-06-055 June 1957 0.5 kt Balloon shot Operation Plumbbob - Lassen.jpg
Wilson 01957-06-1818 June 1957 10 kt Balloon shot Operation Plumbbob - Wilson.jpg
Priscilla 01957-06-2424 June 1957 37 kt Balloon shot Operation Plumbbob - Priscilla.jpg
Coulomb-A 01957-07-011 July 1957 zero yield Safety experiment
Hood 01957-07-055 July 1957 74 kt Balloon shot, largest atmospheric test in the continental United States The fireball from the 74 kiloton "Hood" thermonuclear event as seen from the control point 14 miles from ground zero. Hood was the largest atmospheric nuclear event to occur on the continent. The blast was powerful enough to rattle windows over 300 miles away in California, and the flash was seen by an airline pilot flying over Hawaii, about 2700 miles from the NTS.
Diablo 01957-07-1515 July 1957 17 kt Tower shot Operation Plumbbob - Diablo.jpg
John 01957-07-1919 July 1957 2 kt Live fire of AIR-2 Genie air-to-air rocket Operation Plumbbob - John 2.jpg
Kepler 01957-07-2424 July 1957 10 kt Tower shot Operation Plumbbob - Kepler.jpg
Owens 01957-07-2525 July 1957 9.7 kt Balloon shot Operation Plumbbob - Owens.jpg
Pascal-A 01957-07-2626 July 1957 55 tons Shaft safety experiment. Yield described as slight. Expected yield was 1–2 pounds.[6]
Stokes 01957-08-077 August 1957 19 kt Balloon The tail, or “aft”, section of a U.S. Navy Goodyear ZSG-3 Blimp is shown with the Stokes cloud in background. The blimp was over five miles from ground zero when it was collapsed by the shock wave. The airship was unmanned and was used in military effects experiments on blast and heat. Navy personnel on the ground in the vicinity of the experimental area were unhurt. On the ground to the left are the remains of the blimp's forward section.
Saturn 01957-08-1010 August 1957 Zero yield Shaft safety experiment
Shasta 01957-08-1818 August 1957 17 kt Tower shot Operation Plumbbob - Shasta.jpg
Doppler 01957-08-2323 August 1957 11 kt Balloon shot Operation Plumbbob - Doppler 2.jpg
Pascal-B 01957-08-2727 August 1957 300 tons Shaft safety experiment. Yield often described as slight. Expected yield was 1–2 pounds.[5]
Franklin Prime 01957-08-3030 August 1957 4.7 kt Balloon Franklin Prime test, Operation Plumbbob, Yucca Flat, Nevada - 19570830.jpg
Smoky 01957-08-3131 August 1957 44 kt Tower shot Plumbbob Smoky.jpg
Galileo 01957-09-022 September 1957 11 kt Tower shot Plumbbob Galileo 003.jpg
Wheeler 01957-09-066 September 1957 197 tons Balloon shot Plumbbob Wheeler 001.jpg
Coulomb-B 01957-09-066 September 1957 300 tons Surface safety experiment
Laplace 01957-09-088 September 1957 1 kt Balloon shot Plumbbob Laplace 001.jpg
Fizeau 01957-09-1414 September 1957 11 kt Tower shot Plumbbob Fizeau.jpg
Newton 01957-09-1616 September 1957 12 kt Balloon shot Plumbbob Newton 002.jpg
Rainier 01957-09-1919 September 1957 1.7 kt Tunnel shot. First US underground nuclear test. Plumbbob Rainier 001.jpg
Whitney 01957-09-2323 September 1957 19 kt Tower shot Operation Plumbbob - Whitney.jpg
Charleston 01957-09-2828 September 1957 12 kt Balloon shot Plumbbob Charleston 001.jpg
Morgan 01957-10-077 October 1957 8 kt Balloon Shot Plumbbob Morgan 001.jpg


External links


  1. ^ Dark Circle, DVD release date March 27, 2007, Directors: Judy Irving, Chris Beaver, Ruth Landy. ISBN 0-7670-9304-6. http://www.pbs.org/pov/darkcircle/
  2. ^ Institute of Medicine (U.S.). Committee on Thyroid Screening Related to I-131 Exposure, National Research Council (U.S.). Committee on Exposure of the American People to I-131 from the Nevada Atomic Bomb Tests, ed (1999). Exposure of the American people to Iodine-131 from Nevada nuclear-bomb tests: review of the National Cancer Institute report and public health implications. National Academies Press. pp. 113–114. ISBN 9780309061759. http://books.google.com/books?id=vGtce6RjjM0C&pg=PA114&dq=%22operation+plumbbob%22+OR+nevada+atmospheric+%22thyroid+cancer%22&cd=2#v=onepage&q=%22operation%20plumbbob%22%20OR%20nevada%20atmospheric%20%22thyroid%20cancer%22&f=false. 
  3. ^ Brownlee, Robert R. (June 2002). "Learning to Contain Underground Nuclear Explosions". http://nuclearweaponarchive.org/Usa/Tests/Brownlee.html. Retrieved 2006-07-31. 
  4. ^ Learning to Contain Underground Nuclear Explosions By Dr. Robert R. Brownlee - June 2002
  5. ^ a b Pascal B test at the Nuclear Weapon Archive
  6. ^ Pascal A test at the Nuclear Weapon Archive

Coordinates: 37°08′10″N 116°04′07″W / 37.13611°N 116.06861°W / 37.13611; -116.06861

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