Lahti L-39 Country Anti-tank rifle Type Large caliber rifle Introduction 1939 Specifications Weight 49.5 kg Length 88 inches Barrel length 51.2 inches (130,05 centimeters ) Cartridge 20 mm x 138 mm Solothurn Long Caliber 20 mm Action semi-automatic Rate of fire max. 30/min Muzzle velocity 800 m/s Feed system 10 Rounds

The Lahti L-39 20 mm Anti-Tank Cannon is a Finnish anti-tank rifle used during the Second World War. It had a semi-automatic action and a large magazine. As a result of its large and powerful ammunition the gun had considerable recoil (the perceived recoil, when firing the gun correctly, was actually very tolerable), and its size made portability difficult. As tanks developed armour too thick to be penetrated by even this large, powerful rifle, its uses switched to fields such as long range sniping, tank harassment and an improvised anti-aircraft weapon. Several of the rifles remained in service after World War II even serving as an anti-helicopter weapon.

Aimo Lahti had doubts about the original idea of a 13 mm anti-tank machine gun and started working on a 20 mm design. Officers who wanted smaller calibre anti-tank weapons believed that the muzzle velocity of 20 mm shells was insufficient to penetrate armour and higher rate of fire of a smaller calibre weapon would prove useful. As a result Lahti designed two competing anti-tank weapons: 13.2 mm machine gun and 20 mm rifle. After test firing both weapons in 1939, they found that the 20 mm rifle displayed better penetration.