Most ordinance carried by heavy bombers such as the British Vicker Wellington and Avro Lancaster featured both nose and tail fuzing devices - an impact fuse at the nose and a free wheeling propeller time delay fuse on the tail.
All were secured with arming pins attached to fuzing wire running back up through the bomb bay to a series of grouped spools. The spools were controlled by the Fuzing Unit on the bomb aimer’s control panel which activated a solenoid switch which would lock or release the spool drums.
When set to ‘FUZED’, the unit locked the wire spools via the solenoid and as the bombs fell away from the aircraft, the arming pins were pulled free and armed the bombs. When set to ‘SAFE’ the wire would be pulled off the free running spools and both it and the arming pin would fall free with the bomb - rendering it safe. The ability to jettison a bomb load safely should an engine fail on takeoff or the aircraft experience difficulties over friendly territory was essential to ensure the safety of the aircraft and those below.