Panzer III and Panzer IV's success in the French campaign led the U.S. Army to immediately order a new medium tank armed with a 75 mm gun in a turret as a response. This would be the M4 Sherman but until the Sherman reached production, an interim design with a 75 mm gun was urgently needed. The M3 was the solution. The design was unusual because the main weapon – a larger caliber, medium-velocity 75 mm gun – was in an offset sponson mounted in the hull with limited traverse. The sponson mount was necessary because, at the time, American tank plants did not have the design experience necessary to make a gun turret capable of holding a 75 mm weapon. A small turret with a lighter, high-velocity 37 mm gun sat on top of the tall hull. A small cupola on top of the turret held a machine gun. The use of two main guns was seen on the French Char B1 and the Mark I version of the British Churchill tank. In the French tank, it had been designed as a self-propelled gun to attack fortifications and an anti-tank capability had been added through a second gun in a small turret; the Churchill carried a gun in the front hull to fire chiefly smoke shells. The M3 differed slightly from this pattern, having a dual-purpose main gun that could fire an armor-piercing projectile at a velocity high enough for effectively piercing armor, as well as deliver a high-explosive shell that was large enough to be effective. Using a hull mounted gun, the M3 design could be produced faster than a tank with the same gun in a turret. It was understood that the M3 design was flawed, but Britain urgently needed tanks. A drawback of the sponson mount was that the M3 could not take a hull-down position and use its 75 mm gun at the same time. The M3 was tall and roomy: the power transmission ran through the crew compartment under the turret basket to the gearbox driving the front sprockets. Steering was by differential braking, with a turning circle of . The vertical volute-sprung suspension (VVSS) units possessed a return roller mounted directly atop the main housing of each of the six suspension units (three per side), designed as self-contained and readily replaced modular units bolted to the hull sides. The turret was power-traversed by