Holman Projector - Mk I

Mk I

The design eventually settled on for the Mk I featured a 4½ foot unrifled steel barrel. Rounds were dropped down the barrel and the pneumatic system triggered instantly upon the round striking the base. The rounds themselves were made from an open-topped metal container, holding a Mills bomb fitted with a 3.5 second fuse. High-pressure air bottles were able to supply enough power to fire fifty rounds each, with a maximum height during trials of around 600 feet (180 m). The rate of fire could reach thirty rounds per minute in the hands of an experienced crew. More appealing yet to the armed forces was the fact that the weapon could be produced using only cast iron and mild steel, both of which were in fairly ready supply at this stage of the war.

An official trial of the Mk I Projector took place in February, 1940 with resounding success. An order was placed by the Royal Navy for 1000 of the Mk I models, and the weapons proved just as successful in action; the first confirmed kill reported only three weeks after the initial batch were sent out. While direct hits were rare, the bombs fired by the projector displayed an unexpected property — the explosion would leave a large puff of black smoke, absent from ground-based explosions from similar grenades. Firing a large number in quick succession gave the impression to incoming Luftwaffe pilots that the target vessel was armed with something far more deadly than the Holman Projector.