 Complete the following phrase:  With the launching of Operation Barbarossa on 22 June 1941, the uticipated appearance of the KV-1 and T-34 tanks prompted an upgrade of the Panzer IVs gun to a longer, high-velocity 75 mm gun suitable for anti-tank use. This meant that it could now penetrate the T-34 at ranges of up to at any angle. The 75 mm KwK 40 L43 gun on the Panzer IV could penetrate a T-34 at a variety of impact angles beyond range and up to . Shipment of the first model to mount the new gun, the Ausf. F2, began in spring 1942, and by the 