From my recollection the nose and tail fuses were installed by the armourers when loading the bombs.

Usually there would be an arming wire run from each fuse and this was attached to the aircraft. When the bombs were released the arming wires were pulled out and the fuses then started to arm themselves by the small propellors on each fuse. The bombs had to fall a specified distance before they were armed. This then allowed the aircraft to dump the bombs on takeoff, should they lose an engine, without destroying friendly folks and potentially themselves.

Unlike the B-17’s and 24’s there was no access to the bomb fuses in the bomb bays of the Lanc and the Halifax once the aircraft took off.