Based on the M4A2 and M4A3 Sherman tank chassis, and fitted with a 3-inch M7 gun, the M10 was numerically the most important US tank destroyer of WWII. The M10 was built in response to the stunning successes of the German armoured Blitzkrieg at the outset of the war in Europe. Fitted with a turret - unlike most self-propelled artillery of the era - the vehicle was more heavily gunned but more lightly armoured than a tank. M10 crews were expected to make the most of their vehicles speed and agility. The M10 received its baptism of fire in Tunisia in 1943, where it demonstrated its ability to destroy most German Panzers then in service. The British upgraded the design by rearming some of the 1,700 M10s that they received with the superb Ordnance Quick Firing 17-pounder antitank gun. These vehicles were designated by the British as 17-pounder SP M10 Mark IC/IIC, popularly known as the Achilles.