The Mark 18 nuclear bomb, also known as the SOB or Super

Oralloy Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238U ...

Bomb, was an American nuclear bomb design which was the highest yield

fission bomb 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 ...

produced by the US. The Mark 18 had a design yield of 500

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 m ...

. Noted nuclear weapon designer Ted Taylor was the lead designer for the Mark 18. The Mark 18 was tested once, in the Ivy King nuclear test at the

Enewetak Enewetak Atoll (; also spelled Eniwetok Atoll or sometimes Eniewetok; mh, Ānewetak, , or , ; known to the Japanese as Brown Atoll or Brown Island; ja, ブラウン環礁) is a large coral atoll of 40 islands in the Pacific Ocean and with it ...

atoll in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...

. The test was a complete success at full yield.

Description

The Mark 18 bomb design used an advanced 92-point implosion system, derived from the

Mark 13 nuclear bomb The Mark 13 nuclear bomb and its variant, the W-13 nuclear warhead, were experimental nuclear weapons developed by the United States from 1951 to 1954. The Mark 13 design was based on the earlier Mark 6 nuclear bomb design, which was in turn based ...

and its ancestors the

Mark 6 nuclear bomb The Mark 6 nuclear bomb was an American nuclear bomb based on the earlier Mark 4 nuclear bomb and its predecessor, the Mark 3 Fat Man nuclear bomb design. The Mark 6 was in production from 1951 to 1955 and saw service until 1962. Seven variants ...

Mark 4 nuclear bomb The Mark 4 nuclear bomb was an American implosion-type nuclear bomb based on the earlier Mark 3 Fat Man design, used in the Trinity test and the bombing of Nagasaki. With the Mark 3 needing each individual component to be hand-assembled by only h ...

, and Fat Man Mark 3 nuclear bomb of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

. Its normal mixed

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...

fissile core ("pit") was replaced with over 60 kg of pure

highly enriched uranium Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238U ...

or HEU. With a natural uranium tamper layer, the bomb had over four

critical mass In nuclear engineering, a critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, its nuclear fi ...

es of fissile material in the core, and was unsafe: the accidental detonation of even one of the detonator triggers would likely cause a significant (many kilotons of energy yield) explosion. An

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

/ boron chain designed to absorb

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...

s was placed in the fissile pit to reduce the risk of accidental high yield detonation, and removed during the last steps of the arming sequence.Historical US nuclear weapons
at Globalsecurity.org, accessed April 17, 2007

Deployment

Beginning in March 1953, the United States deployed a number of Mark 18 bombs. A total of 90 were manufactured and placed in service. The weapon had a short lifetime, and was replaced by

thermonuclear weapons A thermonuclear weapon, fusion weapon or hydrogen bomb (H bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lowe ...

in the mid-1950s. The Mark 18 weapons were all modified into lower yield

variants in 1956.

References

{{United States nuclear devices Cold War aerial bombs of the United States Nuclear bombs of the United States Military equipment introduced in the 1950s

Description

Deployment

See also

References