At the start of World War II, only some European nations had an anti-tank rifle based on a high-velocity, large-calibre round, such as the British Boys anti-tank Rifle. The first combat use of anti-tank rifles took place during the invasion of Poland of 1939. The Wz. 35 anti-tank rifle was extensively used by most Polish units. The Wz. 35 with 7.92 mm anti-tank rifle ammunition was a very effective weapon against all German tanks of the period (the Panzer I, II and III, as well as the Czechoslovak-made LT-35 and LT-38).[3] At up to 400 m (1,300 ft), it could destroy all lightly armoured vehicles. It could penetrate 15 mm (0.59 in) of armour, sloped at 30° at 300 m (980 ft) distance, or 33 mm (1.3 in) of armour at 100 m (330 ft).
Later, as armour became thicker on newer models, the effectiveness of a man-portable rifle lessened. This was particularly true in Malaya, where the light Japanese tanks specially configured for jungle conflict rode roughshod over British forces supplied with the Boys anti-tank rifle. At first small cannons up to 20mm 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 such as the bazooka, recoilless rifles such as the Panzerfaust, and rocket-propelled grenades — some anti-armour successes were achieved with heavy-calibre autocannon by the Luftwaffe, especially with the Bordkanone BK 3,7 autocannon, mounted in twin gun pods against Soviet armour on the Eastern Front. 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.
