Upshot–Knothole ''Grable'' was a

nuclear weapons test Nuclear weapons tests are experiments carried out to determine nuclear weapons' effectiveness, yield, and explosive capability. Testing nuclear weapons offers practical information about how the weapons function, how detonations are affected by ...

conducted by the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territo ...

as part of

Operation Upshot–Knothole Operation Upshot–Knothole was a series of eleven nuclear test shots conducted in 1953 at the Nevada Test Site. It followed '' Operation Ivy'' and preceded '' Operation Castle''. Over 21,000 soldiers took part in the ground exercise Desert ...

. Detonation of the associated

nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. Both bomb ...

occurred 19 seconds after its deployment at 8:30am PDT (1530 UTC) on May 25, 1953, in Area 5 of the

Nevada Test Site The Nevada National Security Site (N2S2 or NNSS), known as the Nevada Test Site (NTS) until 2010, is a United States Department of Energy (DOE) reservation located in southeastern Nye County, Nevada, about 65 miles (105 km) northwest of the ...

Nuclear weapons test

The codename ''Grable'' was chosen because the letter ''Grable'' is phonetic for G, as in "gun", since the warhead was a

gun-type fission weapon Gun-type fission weapons are fission-based nuclear weapons whose design assembles their fissile material into a supercritical mass by the use of the "gun" method: shooting one piece of sub-critical material into another. Although this is sometim ...

. As a shell, or artillery-fired atomic projectile (AFAP), the device was the first of its kind. The test remains the only nuclear artillery shell ever actually fired in the U.S. nuclear weapons test program. ''Grable'' was the second of only four gun-type warheads ever detonated (the first was

Little Boy "Little Boy" was the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II, making it the first nuclear weapon used in warfare. The bomb was dropped by the Boeing B-29 Superfortress ''Enola Gay'' ...

, the weapon used against

Hiroshima is the capital of Hiroshima Prefecture in Japan. , the city had an estimated population of 1,199,391. The gross domestic product (GDP) in Greater Hiroshima, Hiroshima Urban Employment Area, was US$61.3 billion as of 2010. Kazumi Matsui h ...

, the last two were test firings of the W33; all other atomic weapons were implosion-type weapons). The shell, designated a

Mark 9 Mark 9 is the ninth chapter of the Gospel of Mark in the New Testament of the Christian Bible. It begins with Jesus' prediction that "I tell you the truth, some who are standing here will not taste death before they see that the kingdom of God h ...

nuclear weapon, had a diameter of 280 mm (11.02 in), was 1380 mm (54.4 in) long and weighed 364 kg (803 lb). The M65 Atomic Cannon from which it was fired had a muzzle velocity of 625 m/s (2,060 ft/s), for a nominal range of , and weighed 77

metric tons The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton (United States c ...

(85 t). The detonation of ''Grable'' occurred 19 seconds after its firing."Operation Upshot–Knothole."
Department of Energy, 1953. It detonated over 11,000 yards (over 10 km, 6.25 mi) away from the gun it was fired from, over a part of the Nevada Test Site known as

Frenchman Flat Frenchman Flat is a hydrographic basin in the Nevada National Security Site south of Yucca Flat and north of Mercury, Nevada. The flat was used as an American nuclear test site and has a dry lake bed (Frenchman Lake) that was used as a 1950s ...

. The explosion was an

air burst An air burst or airburst is the detonation of an explosive device such as an anti-personnel artillery shell or a nuclear weapon in the air instead of on contact with the ground or target. The principal military advantage of an air burst over a ...

of 160 m (524 ft) above the ground (7 m (24 ft) above its designated burst altitude), 26 m (87 ft) west and 41 m (136 ft) south of its target (slightly uprange). Its yield was estimated at 15

kilotons TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. The is a unit of energy defined by that convention to be , which is the approximate energy released in the detonation of a ...

, around the same level as

. An anomalous feature of the blast was the formation of a

precursor Precursor or Precursors may refer to: * Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of u ...

, a second shock front ahead of the incident wave. This precursor was formed when the

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a med ...

reflected off the ground and surpassed the incident wave and Mach stem due to a heated ground air layer and the low burst height. It resulted in a lower overpressure, but higher overall dynamic pressure, which inflicted much more damage on drag sensitive targets such as jeeps and personnel carriers. This led strategists to rethink the importance of low air bursts in tactical

nuclear warfare Nuclear warfare, also known as atomic warfare, is a theoretical military conflict or prepared political strategy that deploys nuclear weaponry. Nuclear weapons are weapons of mass destruction; in contrast to conventional warfare, nuclear wa ...

. Some images from Upshot–Knothole ''Grable'' were accidentally relabeled as belonging to the ''Priscilla'' shot from

Operation Plumbbob Operation Plumbbob was a series of nuclear tests that were conducted between May 28 and October 7, 1957, at the Nevada Test Site, following '' Project 57'', and preceding '' Project 58/58A''. Background The operation consisted of 29 explosion ...

in 1957. As a consequence many publications including official government documents have the photo mislabeled.Carey Sublette, "Operation Plumbbob," Nuclear Weapon Archive
http://nuclearweaponarchive.org/Usa/Tests/Plumbob.html
(accessed December 27, 2006). Admiral

Arthur W. Radford Arthur William Radford (27 February 1896 – 17 August 1973) was an admiral and naval aviator of the United States Navy. In over 40 years of military service, Radford held a variety of positions including the vice chief of Naval Operations, ...

, at the time the Chairman of the Joint Chiefs of Staff, and Secretary of Defense Charles E. Wilson were present for the test.

Footnotes

External links

The Atomic Cannon
archived from AtomCentral {{Nuclear weapons tests of the United States Explosions in 1953 Nevada Test Site nuclear explosive tests 1953 in Nevada 1953 in military history Articles containing video clips May 1953 events in the United States