An anti-tank rifle is a rifle designed to penetrate the armour of vehicles, particularly tanks. The usefulness of rifles for this purpose ran from the introduction of tanks into the Second World War, when they were rendered almost entirely obsolete. Vehicle armour became too thick to be penetrated by rigid projectiles from rifles that could be carried by a single soldier, and anti-tank rifles were replaced with shaped charge weapons of which the best-known is the bazooka.
The first tanks, beginning with the British Mark I, launched against the German trenches in World War I were nearly impregnable to ordinary rifle fire. Most armored cars were similarly invulnerable, but troops rarely faced armored cars, as they could not navigate the landscape of trench warfare very well. Though tanks and armoured cars were vulnerable to artillery, mortars, and grenades, infantry was at a significant disadvantage when facing armored fighting vehicles, since they had no effective direct fire weapon.
The first attempt at boosting penetrating power was the so-called 'reversed bullet'. This used the same cartridge and bullet as the regular round, but the bullet was reversed and an increased propelling charge was used.
The next development was a special armour-piercing bullet, the K bullet (in German Patrone SmK Kurz 7.92 mm), which also could be fired from the regular infantry rifle. It had an increased propelling charge and a steel cored bullet. This had about a 30% chance of penetrating the 8 mm armour of current tanks if it struck the armour at a perpendicular angle.
The K bullet round was more expensive to produce, and therefore it was generally only issued to snipers and other advanced marksmen, who could use it more effectively. The ordinary infantryman had to make do with the reversed bullets which were far less effective and had to be used closer to the target. Other anti-tank weapons such as grenades, mortars, or cannon were preferred. Both types of round damaged the rifles. In the first place there was shortened life through high barrel wear. Secondly, the higher pressure created in the chamber would jam the bolt and only hammering at the stuck bolt would open it. This could lead to the extractor claw failing to extract the cartridge, only breaking off the cartridge rim and leaving it stuck in the gun. The strain of firing the increased charge could also burst the chamber of weaker and older rifles, at best destroying the rifle, at worst injuring or killing the rifleman. For these reasons, the K-bullet and reversed bullet were not popular with the troops. Nevertheless, it gave the infantry a chance to stop a tank in an emergency, or at least injure or kill some of the crew if a bullet penetrated.
Even as the rounds were introduced, tanks were being designed and built with thicker armour rendering these rounds largely ineffective, though they remained in use against the older designs and armoured cars. The first purpose designed infantry anti-tank rifle was designed by Germany. This large-calibre rifle was capable of penetrating the armour of these new generations of tanks and allowed a chance at stopping them. Other techniques were still preferred. The high recoil of the rifle was very hard on the firer, sometimes breaking the collar bone or dislocating the shoulder. Although the rifle was unique to its role, it was a development of the Mauser rifles and high-powered British sporting rifles that had preceded it. The calibre of roughly 12-13 mm was not unusual either; some 0.5 inch firearms having been fielded in land warfare with the relatively new and more powerful (as compared to black powder) smokeless powders of the era.
During WWI, a half-inch high velocity round was being developed in the US at the same time for use against aircraft. It would be used with the Browning-designed .50 calibre machine gun. This round was based on current US .30-06 calibre infantry ammunition. When word of the German anti-tank shell spread, there was some debate as to if it should be copied and used as a base for the new machine gun cartridge. However, after some analysis the German ammunition was ruled out, as its performance was inferior to the modified Springfield .30-06 round and was semi-rimmed, making it difficult to feed into an automatic weapon. The Browning M2 .50 cal machine gun would, however, go on to function as an anti-armour machine gun.
At the start of World War II, most nations had an anti-tank rifle based on a high velocity large calibre round (eg. the British Boys Anti-tank Rifle). These were effective at the start of the war against the early tank designs (light tanks like the German Panzer I and Panzer II). As armor became thicker on the newer models, the effectiveness of a man-portable rifle lessened. A notable exception was against the light tanks employed by the Japanese in Malaya, where the Boys rifle was used with some success. At first small cannons up to 20 mm calibre were used, but the anti-tank role soon required more powerful weapons which were based on the application of chemical energy in the form of the shaped charge anti-tank rifle grenade. To these were added rocket launchers, recoilless rifles such as the Panzerfaust and rocket-propelled grenades such as the bazooka. Some anti-tank rifles, like the Finnish L-39, were still used by snipers to harass the enemy, like firing phosphorus bullets at tanks' open hatches, or to smoke an enemy sniper out of his position.
The Soviet PTRS-41 and PTRD of World War II vintage were used by North Korean and Chinese forces during the Korean War as they lacked more modern infantry anti-tank weapons.
The weapon is the conceptual ancestor of anti-tank weapons wielded by modern infantry, and both large-calibre sniper rifles and anti-materiel rifles owe some part of their design heritage to it.