T-34 was a Soviet medium tank that had a profound and lasting effect on the field of tank design. Although its armour and armament were surpassed later in the war, it has been often credited as the most effective, efficient, and influential tank design of World War II. At its introduction, the T-34 possessed an unprecedented combination of firepower, mobility, protection, and ruggedness. Its 76.2 mm (3 in) high-velocity tank gun provided a substantial increase in firepower over any of the T-34's contemporaries; its heavy sloped armour was difficult to penetrate by most contemporary anti-tank weapons. First encountered in 1941, German tank general von Kleist called it "the finest tank in the world" and Heinz Guderian confirmed the T-34's "vast superiority" over German armour and found it "very worrying".