The Lahti L-39 is a Finnish semi-automatic anti-tank rifle, designed in 1939 by firearms designer Aimo Lahti and used by Finnish forces in the Winter War (1939โ1940) and Continuation War (1941โ1944) against the USSR. It fires the Swiss 20ร138mmB cartridge, which was originally developed for the Solothurn S-18/1000 rifle.