The evolution of tank design throughout the war goes hand-in-hand with that of anti-tank weapons. As larger and more powerful armoured fighting vehicles appeared with progressively heavier armour protection, new guns and new types of ammunition were developed to defend against them. Until the spring of 1941, the main tank and anti-tank (AT) gun used by the British and Canadian armies was the 2-pounder (British guns were frequently named for the weight of projectile they fired).

Soldier firing 6-pounder anti-tank gun at the end of a street in Ortona, Italy, 21 December 1943. Photo by Terry F. Rowe. Department of National Defence / National Archives of Canada, PA-141671.

It had been realised even before the war that a heavier gun was needed, and by 1939 the 6-pounder had been developed, though it did not enter production until November 1941. Following the Dunkirk evacuation, it was decided to continue 2-pdr production because converting the factories for the larger gun would take time. The British were desperately short of guns, and a German invasion was imminent. The 6-pdr subsequently became the main British and Canadian anti-tank gun. For much of the war it was also the standard tank armament, being mounted in Ram and Churchill tanks, among others. By the time of the Normandy invasion in June 1944 the 6-pdr had largely been replaced in tanks and in anti-tank regiments, although it continued to be widely used by the infantry in an anti-tank role.

Personnel of the Royal Canadian Artillery with a 17-pounder anti-tank gun in Normandy, 22 June 1944. Photo by Ken Bell. Department of National Defence / National Archives of Canada, PA- 169273.

The search for a larger gun to replace the 6-pdr led the British to develop the 17-pdr, and issue to the Royal Artillery began in late 1942. The first 17-pdrs had been rushed off to North Africa on 25-pdr carriages to counter the new German Tiger tanks, while development of a proper carriage suited to the 17-pdr continued. By mid-1944 the 17-pdr had become the main weapon in most anti-tank regiments, and a modified version had been fitted into a limited number of Sherman "Firefly" tanks. With the Firefly the British and Canadians had a weapon to compare with the powerful German anti-tank guns. Unfortunately, it was available only in relatively small numbers, and the Americans opted not to use it, preferring to develop their own 76.2 mm gun. Most 17-pdrs were towed, but a self-propelled (SP) variant called the "Archer" featured the gun mounted on a Valentine chassis. It was conspicuous in that the gun was fitted facing the rear of the vehicle. Another SP variant was the "Achilles", basically an American M10 tank destroyer substituting the 17-pdr for the original 3-inch anti-aircraft gun.