An original WWII British No.6 Mk I release switch designed for booby-trap, sabotage, and clandestine demolition work, widely issued to Special Operations Executive (SOE), Office of Strategic Services (OSS), British Commando, and sabotage teams.This device operates as both a pressure and release switch. When armed, tension on the trip wire keeps the striker compressed; removal of tension or release of pressure triggers the striker, which then ignites the connected detonator or explosive charge. The No.6 Mk I was highly versatile, used in sabotage kits, vehicle traps, door traps, and infrastructure demolitions.The example shown is correctly marked: NO 6 B 77 AA, denoting lot and manufacturing batch. The trip wire remains present, which significantly enhances its collector value.