It does what it name says – it takes over a system or a machine if the operator of that system becomes incapacitated or dies. Originally it was meant to save lives if one life is lost.
It was first used in locomotives to bring the engine to an emergency stop should the engineer be unable to fulfill his duties.
Most gas station pumps are switched off by a fail safe button in case of a fire. These are all life saving functions, but the US military saw another application for emergency situation switches.
The Special Weapons Emergency Separation Systems (SWESS) was invented to kill more people if one person dies! It was meant to be a deterrent of sorts. Since the 1950’s Strategic Air Command ensured that all aircraft bombers were fitted with nuclear bomb release systems.
If a bomber was shot down over enemy territory or the controls failed and the plane dropped below a certain altitude, the SWESS automatically released the nuclear weapons on board. These switches were designed for nuclear weapons and are not used to launch missiles because missiles are designed to hit a specific target.
