The British 6 pounder QF AT Gun was the highly successful replacement for the 2-pdr. It was so successful that it was evntually copied by the United States as the M1 57mm gun. Its useful lifespan was extended by new developments in ammunition that improved its armour penetration capabilities, allowing it to knock out Panthers and Tigers from the flank.
The British airborne forces had a special carriage that allowed the 6-pdr to be towed as if it were a light anti-tank gun, making it more mobile and ideal for infantry support roles. Although supplemented by the 17-pdr, it was never entirely replaced and continued to serve in infantry units long after the war ended.
As more became available, the 6-pdr replaced the 2-pdr as the standard weapon in British tanks. Technological advancements in armor were always being improved upon and a replacement was already being sought. HE shells for the 6-pdr were readily available, but the limited size of charge meant they were relatively ineffective and less than ideal as a tank gun. This lead to the development of the 75mm Gun to be used in British tanks such as the Cromwell and Churchill.
