Permissive action link
[1] 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.
More recent innovations have included encrypting the firing parameters it is programmed with, which must be decrypted to properly detonate the warhead, and anti-tamper systems which intentionally mis-detonate the weapon if its other security features are defeated, destroying it without giving rise to a nuclear explosion.
In 1953 the United States Atomic Energy Commission and the Department of Defense signed the Missiles and Rockets Agreement, which paved the way for the development and implementation of PALs.
Certain national laboratories, under the auspices of the AEC, would develop and produce nuclear weapons, while the responsibility for the use and deployment remained with the military.
Newer nuclear weapons were less complex in operation, relatively mass-produced (and therefore predictably similar), and less cumbersome to arm and use than previous designs.
[2] Without Permissive Action Links, each nuclear weapon was effectively under the independent control of one person, the general under whose command it happened to fall.
Back in the days before we had real positive control [i.e., PAL locks], SAC had the power to do a lot of things, and it was in his hands, and he knew it.
In addition, the U.S. realized that in the event of war, parts of West Germany would be overwhelmed early on, and nuclear weapons stationed there could fall into the hands of the Soviet Union.
[4] The precursors of permissive action links were simple mechanical combination locks that were set into the control systems of nuclear weapons, such as the Minuteman ICBM.
In the spring of 1961, there was a series of hearings in Congress, where Sandia presented the prototype of a special electro-mechanical lock, which was then known still as a "proscribed action link".
[citation needed] In June 1962, President John F. Kennedy signed the National Security Action Memorandum number 160.
[7] A 2014 article in Foreign Policy said that the US Air Force told the United States House Committee on Armed Services that "A code consisting of eight zeroes has never been used to enable a MM ICBM, as claimed by Dr. Bruce Blair.
In 1974, U.S. Defense Secretary James Schlesinger found that a variety of tactical nuclear weapons were still not fitted with permissive action links, even though the technology had been available for some time.
In 2002, PALs on older B61 nuclear bombs were replaced and upgraded with new systems to improve reliability and security, as a part of extending the weapons' service lives to at least 2025.
[12] "Bypassing a PAL should be, as one weapons designer graphically put it, about as complex as performing a tonsillectomy while entering the patient from the wrong end.
[14] Modern PALs use the two-man rule, which is designed to prevent accidental or malicious launch of nuclear weapons by a single individual.
The stronglinks include an increased ruggedness of some components and the inclusion of insensitive munitions so that they will not be circumvented by fire, vibration, or magnetic fields, leaving the PAL vulnerable to bypass after such damage.
The ESD determines the external parameters such as acceleration curve, temperature and pressure, and only arms the weapon when these environments are sensed in the correct order.
[citation needed] The US considered this a necessary step: if the technology were kept secret, it would only be half as effective as possible, since the other power in a conflict might not have such safety measures.
Instead, the UK's nuclear bombs to be dropped by aircraft were armed by inserting a key into a simple lock similar to those used to protect bicycles from theft.
However, many experts in the field of nuclear technology in the US government supported the publication of the PAL system because they considered Pakistan's arsenal as the world's most vulnerable to abuse by terrorist groups.
You want to make sure that the guys who have their hands on the weapons can't use them without proper authorization.In November 2007, The New York Times revealed that the US had invested $100 million since 2001 in a secret program to protect Pakistan's nuclear arsenal.
