Ordnance QF 17-pounder Anti-Tank Gun, Royal Canadian Ordnance Corps Museum, Montreal, Québec. The Ordnance QF 17-pounder Anti-Tank Gun was a 76.2-mm (3-inch) gun developed by the British during the Second World War. It was used as an Anti-Tank Gun on its own carriage, as well as equipping a number of British tanks. It was the most effective Allied Anti-Tank Gun of the war. Used with the APDS shot it was capable of defeating all but the thickest armour on German tanks. It was used to ‘up-gun’ some foreign-built vehicles in British service, notably the Sherman 17-pounder Firefly, giving British tank units the ability to hold their own with their German counterparts.