Between 1941 and 1942 the M3 self-propelled gun was the backbone of the US anti-tank division. Consisting of the M3 half-track with mounted 36 caliber 75 mm anti-tank gun, it proved ineffective in fighting German armour, calling for a more manoeuvrable tank destroyer with increased firepower. In November 1941 a prototype T35 tank destroyer was manufactured. Officially adopted in June 1942 under the designation M10, it was the US Army's first full-track tank destroyer. The M10 had the lower chassis from the M4A2 Sherman, but was fitted with a lower, redesigned upper section. Designed for maximum manoeuvrability, the M10's armour was relatively thin. To compensate for this weakness, an angled chassis was chosen to increase bullet deflection. A 50 caliber M7 3-inch (76.2 mm) cannon was mounted in the rotating, open-topped turret. Firing M62 capped armour-piercing shells (APC), the M7 3 gun could penetrate 88 mm armour at a range of 1000 m with an impact angle of up to 30 degrees. The M10 featured a GMC 6064 (or 6064D) 2-stroke water-cooled diesel engine that produced 375hp for a top speed of 48 km/h. The M10 was fitted with a counterweight at the rear of the turret, with early designs carrying box weights and later triangular weights. Serial production ran from September 1942 to December 1943 for a total of 6706 vehicles, including those with M10A1 petrol engines.