The M4 used an angular shaped welded hull, and the Continental R975-C1 radial aircraft engine. Although powerful and proven, its high center propeller shaft gave the hull a tall profile. Suspension was a rugged and simple design, known as VVSS (Vertical Volute Spring Suspension), with three units (or bogies) on each side, and each with two road wheels. The transmission was 5-speed forward, plus reverse. Early production M4's had a 3-piece front transmission cover, and a cast one-piece steel turret mounting a 75mm main gun. For added protection, applique armor plates were added to the turret, hull sides and just in front of the forward hull hatches. Production of the M4 began in July 1942, five months later than the cast hulled M4A1. It was first deployed during the Italian campaign in May 1943. Although outgunned by the German Panzers, the M4's superb reliability, mobility and superior numbers, compensated for the smaller weapon. M4 Sherman tanks saw action on every front, from its introduction in Italy, to the end of the conflict.