Two subjects dominated fashionable military thinking in the 1920s and 1930s; firstly, the supposed omnipotence of the heavy bomber, and secondly the growing role of armoured warfare. The generation of Great War generals who thought of tanks as pale substitutes for horses had retired, discredited, whilst thinkers such as Basil Liddell-Hart and Heinz Guderian pontificated on a vision of future war fought with fast-moving, well-organised machines. Unfortunately for the world, Liddell-Hart's ideas were more influential in Germany than Britain, but that is another story.

The late 1930s saw the sophistication, firepower and armour protection of tanks advance beyond the ability of infantry to combat them. The vision of massed tank warfare did not materialise, as none of the major participants could afford such an arsenal, at least not in the early stages of the war; Germany's blitzkrieg was a matter of concentrating its limited resources in key locations, against an unprepared, weak enemy which had spread itself thinly over the French/German border. British and French troops could not count on support from tanks.

On the metal web the most precarious position was held by the infantry. Not much thought had been given to infantry anti-tank weapons during the latter part of the 1930s. Soldiers could call on a variety of methods to deal with enemy tanks, none of which were particularly successful. They could bring down artillery barrages, if artillery was available, if there was a way of communicating with the artillery, if there was a way to bring it to bear in the right place, assuming that the shells actually hit anything. The soldiers could use their anti-tank rifles - heavy, cumbrous high-velocity rifles firing machine-gun bullets, ancestors of some modern sniper weapons, but of little use against tanks. They could, if they were so equipped, emplace their static two-pounder anti-tank guns and hope that they could get the first shot in. Or they could close with the panzers and throw grenades at their tracks.

Thus the PIAT, 'Projector, Infantry, Anti-Tank', Britain's equivalent of the American bazooka, although with a different and unusual mechanism. Whereas the bazooka fired rockets through a hollow tube, the PIAT was an odd cross between shoulder-fired mortar, spring-powered air rifle and grenade launcher. The PIAT was braced against the shoulder, there being no backblast. Unlike the bazooka and other rocket weapons (such as the German 'Panzerfaust'), it could therefore be used indoors, with one's back to the wall. Its short range and low-velocity projectile allowed it to serve double duty as a makeshift mortar, firing high explosive projectiles up in the air, whilst a smaller projectile charge ensured that there was a less smoke to give away the firer's position. Indeed the projectile was essentially a large bullet rather than a rocket, its charge detonating instantly, leaving no smoke trail through the air.

The PIAT's mechanism was unique, based around a large spring. On firing, the spring-loaded firing pin was driven into the base of the round, whereupon it detonated a propellant charge. In principle this is no different to most small arms, but the PIAT's spring acted as an assist for the main charge, providing twelve pounds of extra motive force. The round weighed three pounds and travelled at 250 feet per second for a maximum effective range of 300 feet, although at that distance the user had to be a crack shot, capable of judging elevation instinctively. The maximum point-blank zero range was less than 100 feet, although fortunately the PIAT's shaped-charge warhead was equally effective at any range, its destructive power resulting from the configuration of the explosive rather than its velocity.

In common with spring air rifles, the PIAT had an unusual multi-stage recoil, a combination of the round's explosive charge detonating against the firing pin, and the motion of the internal spring. An extremely heavy trigger pull impaired accuracy, whilst the necessity of cocking the spring did not endear the device to its users. The spring required 90kg of force to cock, the user bracing the base of the PIAT against his feet and stretching his upper body, as with some modern exercise equipment. The PIAT was theoretically re-cocked by the recoil of each round, although this was not always the case, especially if the user did not brace the weapon firmly enough. The PIAT could be fired from a prone position, another advantage over traditional rocket launchers.

The PIAT's mechanism and general design were derived from the Blacker Bombard, a larger weapon devised by a Lieutenant Colonel Blacker in 1940. Whilst the Bombard was only issued to Home Guard units, and then as an emergency measure, the PIAT was a great success. It was adopted by the Canadian military and continued in British service until 1951, albeit that this was mostly as a result of post-war austerity. Although the PIAT was cumbersome, of short range, weighing over thirty pounds, its warhead was slightly more powerful than early American and German designs, penetrating five inches of steel plate when hit square-on. Despite this, soldiers could not expect a frontal hit to penetrate the armour of the more advanced tanks, although the PIAT's facility for indoors use allowed more possibilities for creating ambushes in built-up fighting. The airborne forces dropped into Arnhem in the disastrous Operation Market-Garden (chronicled in the book and film 'A Bridge Too Far') relied heavily on their PIATs.

The use of PIATs produced three Victoria Crosses, all won in 1944. Privates Francis Arthur Jefferson, Ernest Smith, and Ganju Lama (British, Canadian, and Nepalese respectively) all won VCs for engaging and destroying German and Japanese tanks whilst under fire. As with other anti-tank weapons it was impossible to 'snap-shoot' with the PIAT, and furthermore the fiddly reloading procedure compelled the user to hit his target with the first shot. That soldiers were issued bravery awards for engaging tanks with a purpose-built anti-tank weapon suggests that, for all the PIAT's virtues, it was a brave soldier indeed who actually faced off against a tank armed with one.

By the end of the WW2 the PIAT had become an evolutionary dead-end, its spring-loaded mechanism being heavier and more complex than a simple rocket tube. From 1951 the PIAT was briefly replaced in British service by the American bazooka, and then by a combination of the Swedish 84mm Carl Gustav and the American 66mm LAW, a weapon based on the disposable, single-shot philosophy of the German Panzerfaust. The latter is still used widely today.