High Quality Content by WIKIPEDIA articles! The Sherman Firefly was a World War II British and Canadian variation of the American Sherman tank, fitted with the powerful British 17 pounder anti-tank gun as its main weapon. Originally conceived as a stopgap tank until future British tank designs armed with the 17 pounder came into service, the Sherman Firefly became the most common vehicle to be used with the 17 pounder as its main armament during World War II. The concept of fitting a 17 pounder gun into a Sherman tank had initially been rejected by the Ministry of Supply's Tank Decision Board because of its use of an American Sherman tank as a mount for the gun. The British Army had decided in early 1943 that, with the emergence of the new British tanks designs that at the time were to be superior to American supplied tanks, the British Army would once again start equipping their armoured divisions with British tanks rather than American ones.