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Permissive action link

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A Permissive Action Link is a security device for nuclear weapons. The United States Department of Defense definition is:

A device included in or attached to a nuclear weapon system to preclude arming and/or launching until the insertion of a prescribed discrete code or combination. It may include equipment and cabling external to the weapon or weapon system to activate components within the weapon or weapon system.

The earliest PALs were little more than locks introduced into the control systems of a nuclear weapon, that would inhibit either the detonation, or the removal of safety features of the weapon. More recent innovations have included encrypted firing parameters, which must be decrypted to properly detonate the warhead, and anti-tamper systems that intentionally mis-detonate the weapon, destroying it without giving rise to a useful nuclear explosion.

These combination locks were installed on Minuteman ICBMs in the 1960s. However, the Strategic Air Command in Omaha worried that in case of need the codes would not be available, so they quietly decided to set them to 00000000; checking this combination was even present on the launch checklists. This was not changed until 1977.[1] In 2007 the British Government revealed that its Nuclear Weapons were not equipped with Permissive Action Links. [2].

PAL devices were also installed on Sergeant, Pershing, and WAC Corporal missiles as well as the Nike-Hercules, Honest John rockets, the Davy Crockett system, and 155mm Howitzer, 8 inch howitzer rounds.

The PAL or PAL-like devices have been portrayed in various settings by the entertainment industry, such as in the computer game Metal Gear Solid, the motion picture WarGames, and the television series 24 season 4.

References

  1. ^ Keeping Presidents in the Nuclear Dark (Episode #1: The Case of the Missing “Permissive Action Links”) - Bruce G. Blair, Ph.D
  2. ^ BBC NEWS | Programmes | Newsnight | British nukes were protected by bike locks

See also

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