A Holman Projector prepared for early trials at Porthtowan. A crude anti-aircraft sight is fitted to the mortar barrel.
Type Grenade Projector
Place of origin United Kingdom
The Holman Projector was an anti-aircraft weapon used by the Royal Navy during World War II, primarily between early 1940 and late 1941. The weapon was proposed and designed by Holmans, a machine tool manufacturer based at Camborne, Cornwall. A number of models were produced during the war years, but all worked on the principle of a pneumatic mortar, using compressed air or high pressure steam to fire an explosive projectile at enemy aircraft.
Holmans specialised in producing gas compressors and pneumatic equipment and its owner, Treve Holman, conceived a way that his firm could aid in the war effort beyond the production of tools. Recalling the World War I-era Stokes Mortar and its successor, the Ordnance ML 3 inch Mortar, Holman believed that it would be possible to produce a version powered by compressed air. Preliminary tests showed that the idea was feasible, with an early prototype throwing an eighteen-pound steel weight nearly 100 yards (91 m).
Mk IThe 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.
Mk IIThe Mk II Projector was developed after a request from the Royal Navy for a version that could be fired using steam in place of compressed air, since the steam trawlers (both fishing and minesweeping) had the former in plentiful supply. The Stokes design of the Mk I needed to be abandoned for this, since the harsh weather experienced by the trawlers invariably rusted the valves of the pneumatics. When steam was used in such a system, the water would condense in the pipes and prevent firing of the weapon. To solve this, a firing trigger was added, in place of the Stokes design in which the round would be fired automatically.
This new version was fitted to a wide variety of ships, from destroyers to minesweepers and motor gun boats. To demonstrate the weapon's versatility, a trial was arranged in Aldershot, Hampshire in front of the Prime Minister, Winston Churchill. No Mills rounds were brought, as it was assumed that some form of ammunition would be provided by the British Army, who were overseeing the trials. As it turned out, this was overlooked and the trial was delayed until one officer thought to bring out the bottles of beer that had been brought to serve at lunch. The smooth bore of the Projector allowed even these irregular projectiles to be fired successfully, with all striking the target with an explosion of glass and foam. The Prime Minister commented on the weapon afterwards, describing it as "A very good idea, this weapon of yours. It will save our cordite".
Regardless of the successful trials, The Mk II was still highly inaccurate when fired at distant moving targets. Only a dozen or so aircraft were confirmed to have been downed by the weapon in its first year of service. It did, however, succeed in convincing many more aircraft that the target vessel was more heavily equipped than it actually was, and a large number of reports were made about Luftwaffe aircraft turning away from an attack after salvoes from the ship's Holman Projector were launched. Within the Admiralty, the perception was that the Projector was a useful stop-gap weapon in the early years of the war, when other more effective anti aircraft weaponry, such as the Oerlikon 20 mm cannon, were in short supply.
Mk IIIIn 1941, production of the Mk III Holman Projector began. This version was semi-automatic, and capable of firing multiple projectiles in a single salvo to a height of around 1,000 feet (300 m). The Admiralty placed an order for a further one thousand units, to be fitted to coastal gunboats and other light craft, where the light recoil of the weapon had proven useful. Plans were drawn up for a Mk IV version of the Projector to fill this niche more readily, with a shorter barrel and swivel base. However, by the time the plans were ready to be put into action the war had progressed, and more advanced weaponry was now available that made the Projector obsolete. A number of the earlier model Projectors still played a part in the conflict though, discouraging attacks in the Mediterranean by some smaller submarines, and a small number were adapted to fire grapnels for commando cliff assaults. In total around 4,500 Holman Projectors were put into active service during World War II, and several can still be found in museums in the United Kingdom.