“The PIAT is actually a load of rubbish, really,” said Sgt. M.C. Thornton in Stephen Ambrose’s book Pegasus Bridge, and that has generally been the verdict of history with respect to the Projector Infantry Anti Tank, always simply known as the PIAT.
At the beginning of World War II, the British infantry were armed with two principle anti-tank weapons: the Boys anti-tank rifle, and the No. 68 grenade. The Boys anti-tank rifle was, basically, a .55-caliber bolt-action rifle. It was 5 ft. 2 in. long, all told, and weighed more than 35 pounds. It was effective against some armored cars and Italian light tanks early in the war, but was quickly outmatched by more heavily armored vehicles. And no one wanted to carry it. The No. 68 grenade worked on the shaped-charge principle, and was fired from a cup discharger mounted on the end of a standard Enfield bolt-action rifle. It could penetrate up to two inches of armor but soon two inches wasn’t enough. What was needed was a bigger projectile, but a bigger projectile couldn’t be launched by a rifle.
The solution was found in a spigot mortar. While a typical mortar has a fixed firing pin at the bottom of the tube, onto which the mortar bombs are dropped tail first, a spigot mortar propels the firing pin into the base of the stationary bomb. In the case of the PIAT, this was performed by a very large spring. It was, in essence, a horizontal mortar.
The concept was simplicity itself, as was the construction. The PIAT was a simple tube, with a tray at the front in which the firer placed the bomb. At the other end of the tube was a padded buttplate, and underneath the tube, about midway down its length, a pistol grip and gigantic trigger guard housing the “trigger,” which was really more of a handle, having to be pulled with the entire hand. Just in front of that was a simple monopod on which to rest the nose-heavy weapon.
The problem came with operating it. First of all, you had to cock it. For this, the soldier had to rotate the buttplate to unlock it, then stand on it while pulling up on the trigger guard against a 200-pound spring. Although it could be done while lying prone, that was reportedly even more difficult. Once the PIAT was cocked, the firer lay down in a prone position, the buttplate held firmly to his shoulder. Once the trigger was pulled, the spring loaded spigot drove into the bottom of the bomb, and a small charge propelled it through the air to a maximum range of about 100 yards. Firing the PIAT was supposed to drive the spring back into a cocked position, but if the PIAT wasn’t held firmly against the shoulder it not only delivered a mighty wallop, but would fail to recock itself.
“The range is about 50 yards and no more,” said Thornton. “You’re a dead loss if you try to go farther. Even fifty yards is stretching it, very much so. Another thing is that you must never, never miss. If you do, you’ve had it, because by the time you reload the thing and cock it, which is a bloody chore on its own, everything’s gone, you’re done. It’s indoctrinated into your brain that you mustn’t miss.”
That said, at close range it was effective. Thornton himself destroyed a German Pzkw Mk. IV at Pegasus Bridge with a PIAT. It also had an advantage that rocket launchers do not: because there is no back blast it can be fired from indoors or in confined spaces, and with little muzzle flash is harder for the opposing tank to locate, and British airborne soldiers at Arnhem held out against German armor with their PIATs when they had nothing else. Whatever its limitations, it remained in service until the 1950s.