The Emergency Disablement System described below was adopted as a classified nuclear weapon intrusion counter-measure in the mid 1980s. It allows nuclear task force commanders to remotely disable individual weapons or groups of warheads in the event of a terrorist attack or intrusion.

It could also be used as a prototype for all sorts of arms control measures. In the 1970s, the Pentagon briefly considered a program to add the EDS to all deployed systems, but there was little political will to make the change. Commanders didn’t want another complicated electronic system around the warheads that would potentially mess up the nuclear control order … they wanted to be able to launch as soon as possible. But a growing attention to the possibility that the Soviets could use electronic warfare to fry U.S. nuclear electronics and spoof commands to and from launch control centers made the adoption of EDS an imperative.

Here’s the only unclassified document I’ve been able to find about the EDS.