The 7.5 cm KwK 42 L/70 (from 7.5 cm Kampfwagenkanone 42 L/70) was a 7.5 cm calibre German tank gun developed and built by Rheinmetall-Borsig AG in Unterlüß during the Second World War. The gun was used to equip the SdKfz.171 Panther medium tank and the SdKfz.162/1 Jagdpanzer IV/70(A)/(V) tank destroyer. When mounted on a tank destroyer it was designated as the 7.5 cm PaK 42 (7.5 cm Panzerabwehrkanone 42).

The key feature of the weapon was its high muzzle velocity which enabled high accuracy and good penetration capabilities.When the 7.5 cm KwK 42 entered service with the Panther in 1943 it could penetrate more armor than any Soviet, American or British tank gun then in service. In this respect it was even more powerful than the Tiger's famous 8.8 cm KwK 36 L/56. The KwK 42 however fired a weaker HE shell.

The increased muzzle velocity and operating pressure of the new gun required a new armour piercing projectile to be designed. The PzGr. 39/42 was the result, and apart from the addition of wider driving bands it was otherwise identical to the older 7.5 cm Pzgr.39. The wider driving bands added a little extra weight, from 6.8 kg for the old PzGr.39, to 7.2 kg for the new PzGr.39/42.