Editing Permissive action link (section)

=={{Anchor|Category}} Versions ==
[[File:Nuclear missile launch keys.jpg|thumb|right|upright|Simulated [[LGM-118 Peacekeeper|Peacekeeper]] missile launch (with a [[house key]] shown, rather than an actual missile system key)]]
Over the years the design and feature set of PALs has increased, as has the length of the access code. US-manufactured PALs are divided into five categories; however, the earliest PALs were never assigned a category letter.
{| class="wikitable sortable" style="text-align:center"
|-
! Category
! Code length
! class="unsortable" | Description
|-
| {{SortKey|1|'''–'''}} || {{SortKey|1|3–4}}
| style="text-align:left;" | Combination locks with a three-number sequence. Later versions used five numbers, so that the access code could be divided between two people, each of whom would only know half of the sequence with a commonly known number in between.
|-
| {{SortKey|2|'''A'''}} || {{SortKey|2|4}}
| style="text-align:left;" | Electromechanical switches designed for ballistic missiles. The four-digit code was entered into the weapon using a portable electronic device.
|-
| {{SortKey|3|'''B'''}} || {{SortKey|3|4}}
| style="text-align:left;" | Essentially identical in function to category A, but designed with newer technology. Additionally, they could be activated via a wired remote, and were thus used on weapons launched by aircraft.
|-
| {{SortKey|4|'''C'''}} || {{SortKey|4|6}}
| style="text-align:left;" | Featured a six-digit switch, and allowed for only limited code attempts before lockout. Such behavior was pioneered in some late model category B PALs.
|-
| {{SortKey|5|'''D'''}} || {{SortKey|5|6}}
| style="text-align:left;" | All the features of the previous generation, but also allowed for the input of multiple types of codes, including ones that could set the device to a training mode, or disable the weapon entirely.
|-
| {{SortKey|6|'''F'''}} || {{SortKey|6|12}}
| style="text-align:left;" | Expanded the code length to 12 digits, and disabled the weapon in addition to lockout after a series of failed code entry attempts. They also include the ability to control the magnitude of the nuclear reaction (the so-called [[variable yield|dial-a-yield]] feature) and an emergency stop.<ref>Thomas B. Cochran, William M. Arkin, Milton M. Hoenig: ''Nuclear Weapons Databook: Volume I - U.S. Nuclear Forces and Capabilities.'' Ballinger Publishing Company, Pensacola 1984, {{ISBN|978-0-88410-173-4}}.</ref>
|}
{{Clear}}