The M4A3 Sherman was armed with the standard M3 75mm gun plus a T34 Calliope - a 60-tube tank mounted rocket launcher which fired 4.6 inch rockets. The Calliope was generally mounted on top of an M4 Sherman tank and served within US armour units from 1944 onwards albeit in small numbers. The elevation of the rocket tubes was controlled by connecting them to the main 75mm gun.