A medium tank is a classification of tanks, particularly prevalent during World War II which represented a compromise between the mobility oriented light tanks and the armour and armament oriented heavy tanks. A medium tank's classification is not actually based on weight, but off of tactical usage and intended purpose; for instance the German Panzerkampfwagen V Panther medium tank has a mass similar to contemporary Allied heavy tanks. The most widely produced, cost effective and successful tanks of World War II (the German Panzer IV, the Soviet T-34, and the American M4 Sherman) were all medium tank designs. Many of the medium tank lines became what are called main battle tanks in most countries.