Rheinmetall began the studies of a new antitank 75 mm gun in the Summer of 1939. It was in many counts the bigger brother of the 50mm Pak 38, to which it is visually very similar (only the size makes possible to tell them apart). Started leisurely, the development became an emergency when the Russian tanks T-34 and KV-1 rendered the existing German antitank weapons irrelevant in the Summer of 1941. The first examples reached the frontline in November of 1941 and proved a formidable tank killer. It could pierce 120 mm armor at a distance of one kilometer ! The chamber was wider than the barrel, so that the combustion of the propellant continued during the travel of the shell in the barrel. The main drawback of the new weapon was its weight: a large vehicle was necessary to move it, which was detrimental to the discretion of antitank positions. A smaller variant, the 75mm Pak 50, was tried unsuccessfully to remedy that problem. It had other adaptations to fit it on tanks and even on aircraft
