This canister and hand grenade were ammunition for a Holman Projector, a stop-gap anti-aircraft weapon fitted to many merchant ships.

The tube-like Holman Projector fired hand grenades in containers like these into the air using steam from the ship's boilers. The two-part metal canister held a standard hand grenade (right) and kept the lever that armed it from moving until air resistance pulled the canister away after it was fired from the projector. Exploding a few seconds later, the grenade produced a cloud of fragments and a puff of smoke. While the Holman Projector posed little actual threat to aircraft, the grenades' visible explosions may have helped deter enemy pilots.

Canister, Mk II N
CWM 20070067-547
Grenade, 36M
CWM 19740189-005