It was based on the ubiquitous US M4 Sherman tank, but fitted with the powerful 3-inch (76.2 mm) caliber British 17-pounder anti-tank gun as its main weapon to counter the heavy armor used by Germany's Wehrmacht in the European theater.
Originally conceived as a stopgap until future more powerful British tank designs came into service, the Sherman Firefly became the most common vehicle mounting the 17-pounder in the war. While the weapon proved effective against the heavier German tanks, it was difficult to use due to the excess of fumes produced by firing the gun in the cramped turret of the vehicle, which greatly impaired visibility during battle.
