Mark 7 nuclear bomb

Mark 7 "Thor" (or Mk-7'[1]) was the first tactical fission bomb adopted by US armed forces. It was also the first weapon to be delivered using the toss method with the help of the low-altitude bombing system (LABS). The weapon was tested in Operation Buster-Jangle. To facilitate external carry by fighter-bomber aircraft, Mark 7 was fitted with retractable stabilizer fins. The Mark 7 warhead (W7) also formed the basis of the 30.5 inches (775 mm) BOAR rocket, the Mark 90 Betty nuclear depth charge, MGR-1 Honest John rocket, and MGM-5 Corporal ballistic missile. It was also supplied for delivery by Royal Air Force Canberra aircraft assigned to NATO in Germany under the command of SACEUR. This was done under the auspices of Project E, an agreement between the United States and the UK on the RAF carriage of US nuclear weapons. In UK use it was designated 1,650 lb. H.E. M.C.[2] The Mark 7 was in service from 1952 to 1967(8) with 1700–1800 having been built.[3]

Mark 7
Mark 7 nuclear bomb at USAF Museum
TypeNuclear bomb
Service history
Used byUnited States
Production history
ProducedJuly 1952 to February 1963
No. built3,050 to 3,150 weapons produced in all variants.
Variants10
Specifications
Mass1,600 pounds (730 kg)
Length15 feet 2 inches (4.62 m)
Diameter30 inches (76 cm)
Blast yield8, 19, 22, 30, 31, and 61 kt by using different weapon pits.

Design
See also: Nuclear weapon design
Diagram of implosion system like that used in the Mk7

The Mark 7 was a variable yield fission weapon using a levitated pit and an implosion design using 92 high explosive lenses. The weapon had multiple yields of 8, 19, 22, 30, 31, and 61 kt by using different weapon pits.[4] The weapon had both an airburst and contact fuzing modes. The weapon used in flight insertion for safing and later versions of the weapon used a PAL A type arming and safing system. Approximately 1700 to 1800 Mark 7 bombs and 1350 W7 warheads were produced.[3][5]

The Mark 7 nuclear weapon weighed approximately 1,600 pounds (730 kg).[6] It was fitted with one vertical retractable stabilizer fin that allowed it to fit better in or under some planes.[1] This was unique, and made it one of the first nuclear weapons to be streamlined enough to be carried on smaller planes.[7] The bomb’s diameter is a total of 30 inches (760 mm).[6]

Delivery system

There were 10 different models of this warhead produced for several different delivery systems. Beside the Mark 7 bomb, this included the BOAR air-to-surface rocket, the MGR-1 Honest John and MGM-5 Corporal tactical surface-to-surface missiles, the Betty Mark 90 depth bomb, the MIM-14 Nike Hercules surface-to-air missile and an atomic demolition munition.[3]

Configured as a Mark 7 gravity bomb and as the BOAR, the weapon was carried by the F-84 Thunderjet, F-100 Super Sabre and F-101 Voodoo fighter-bombers, and the B-57 Canberra bomber.[1]

Tests

During Operation Teapot MET on 15 April 1955 a test was conducted using a Mk7 warhead using an experimental composite plutonium/uranium-233 pit, producing a 22kt yield, 33% lower than expected. As Shot MET was a military effects test the lower yield ruined many of the experiments being conducted by the DoD during the test. The DoD had not been informed of the substitution by Los Alamos.[6][8][9]

Survivors

A Mark 7 casing is on display in the Cold War hangar at the National Museum of the United States Air Force in Dayton, Ohio.

Specifications

Users
A Douglas A4D-2 carrying a Mk 7 bomb on the USS Saratoga in the early 1960s

See also

References
  1. USAF Museum: Mk 7 nuclear bomb Archived 2007-10-28 at the Wayback Machine
  2. Canberra B.6 & B.(I)6. Pilot's Notes, 1958
  3. Complete List of All U.S. Nuclear Weapons
  4. Hansen, Chuck (2007). Swords of Armageddon: U.S. Nuclear Weapons Development since 1945 Volume I. Chucklea Publications. p. 282. ISBN 978-0-9791915-0-3.
  5. FISSION WEAPONS from Department of Energy (DOE) OpenNet documents
  6. New Postwar Explosives
  7. Nuclear Weapons
  8. "Operation Teapot". Nuclear Weapon Archive. October 15, 1997. Retrieved 30 November 2018. "The predicted yield was 33 kt. The actual 22 kt was 33% below this, seriously compromising the data collected." cf. "Nuclear Test Film - Operation Teapot" (linked below) ~17:30 "While the expected yield was 28 kilotons, radiochemical analysis indicated a yield closer to 22 kilotons."
  9. "Operation Buster-Jangle". Nuclear Weapon Archive. October 15, 1997. Retrieved 30 November 2018.
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