As the StuG was designed to fill an infantry close support combat role, early models were fitted with a howitzer-pattern, low-velocity 7.5 cm StuK 37 L/24 gun, much as the earliest versions of the fully turreted Panzer IV were. Low-velocity shells are lightly built of thin steel and carry a large charge of explosive, to destroy soft-skin targets and blast fortifications. Such shells do not penetrate armour well. After the Germans encountered the Soviet KV-1 and T-34 tanks, the StuG was first equipped with a high-velocity 7.5 cm StuK 40 L/43 main gun (spring 1942) and in the autumn of 1942 with the slightly longer 7.5 cm StuK 40 L/48 gun. These high-velocity guns were the same as those mounted on the Panzer IV for anti-tank use but the heavy steel wall high-velocity shells carried much less explosive and had a lower blast effect for use against infantry or field fortifications. These versions were known as the "7.5 cm Sturmgeschütz 40 Ausf.F", "Ausf. F/8" and " Ausf. G (Sd.Kfz.142/1)".