Editing Permissive action link (section)

=== Development and dissemination ===
The precursors of permissive action links were simple mechanical [[combination lock]]s that were set into the control systems of nuclear weapons, such as the [[LGM-30 Minuteman|Minuteman]] [[ICBM]]. There they could perform different functions: some blocked the cavity through which the nuclear materials were [[Gun-type fission weapon|shot]] to create a reaction; other locks blocked circuits; and some simply prevented access to the control panel. For testing, some of these mechanisms were installed during 1959 in weapons stationed in Europe.<ref>''Weapon Dispersal without Fear of Unauthorized Use.'' In: ''Sandia Lab News'', Family Day Special Edition, Bd.&nbsp;38 Nr.&nbsp;20, 1986, S.&nbsp;4.</ref>

The work on PAL prototypes remained at low levels until 1960. [[Sandia National Laboratories]] successfully created a number of new combination locks that were adaptable to different types of weapons. 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".  The military leadership, however, soon realized that this term had negative connotations for the use of weapons by the officer corps ("proscribed" meaning "prohibited"), and decided to start calling PAL "permissive action link" instead ("permissive" meaning "allowing" or "tolerating").{{citation needed|date=August 2017}}

[[File:NSAM 160.jpg|thumb|right| National Security Action Memorandum 160: introduction of PAL to all U.S. nuclear weapons under [[NATO]] command]]

In June 1962, President [[John F. Kennedy]] signed the [[National security directive|National Security Action Memorandum]] number 160. This presidential directive ordered the installation of PALs in all U.S. nuclear weapons in Europe. (U.S. nuclear weapons that were not in Europe were excluded from the order.) The conversion was completed in September 1962 and cost $23 million (${{Formatprice|{{Inflation|US|23000000|1962|r=-6}}}} in {{Inflation-year|US}} dollars{{Inflation-fn|US}}).

According to nuclear safety expert [[Bruce G. Blair]], the US Air Force's [[Strategic Air Command]] worried that in times of need the codes for the Minuteman ICBM force would not be available, so it decided to set the codes to 00000000 in all [[missile launch control center]]s. Blair said the missile launch checklists included an item confirming this combination until 1977.<ref>{{cite web|url=http://www.cdi.org/blair/permissive-action-links.cfm |title=Keeping Presidents in the Nuclear Dark (Episode #1: The Case of the Missing "Permissive Action Links") - Bruce G. Blair, Ph.D |publisher=Cdi.org |date=February 11, 2004 |access-date=April 29, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20120511191600/http://www.cdi.org/blair/permissive-action-links.cfm |archive-date=May 11, 2012 }}</ref> 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."<ref>{{cite magazine|last1=Lamothe|first1=Dan|title=Air Force Swears: Our Nuke Launch Code Was Never '00000000'|url=https://foreignpolicy.com/2014/01/21/air-force-swears-our-nuke-launch-code-was-never-00000000/|access-date=24 January 2017|magazine=Foreign Policy|date=2014-01-21|archive-date=March 29, 2017|archive-url=https://web.archive.org/web/20170329185801/http://foreignpolicy.com/2014/01/21/air-force-swears-our-nuke-launch-code-was-never-00000000/|url-status=live}}</ref> The Air Force's statement (that 00000000 was never ''used'' to enable an ICBM, i.e. the weapons were not actually launched) does not contradict Blair's statement (that 00000000 was the code for doing so).

The complete conversion to PAL systems was relatively slow. 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.<ref name="Insider">Thomas C. Reed: ''At the Abyss: An Insider’s History of the Cold War.'' Presidio Press, New York 2005, {{ISBN|978-0-89141-837-5}}.</ref> It took another two years until all the tactical nuclear weapons were fully equipped with PALs. In 1981, almost 20 years after the invention of PALs, just over half of U.S. nuclear weapons were still equipped only with mechanical locks.<ref name="Assuring Control"/> It took until 1987 until these were completely replaced.