The decision to convert redundant tanks into personnel carriers was inspired by Allied experiences during the D-Day landings, where British and Canadian forces experienced much lower casualty rates by leading attacks on German lines with armour than did the Americans, who led with an infantry assault. To General Guy Simonds, who was ordered to follow up the D-Day attacks with an assault on Falaise, this experience suggested both the usefulness of such armour-first tactics, as well as the further benefits of using armoured vehicles to transport troops, leading him to stress the issue while planning his assault, deeming it essential "...that the infantry must be carried in bullet-proof and splinter-proof vehicles to the actual objectives." No such vehicles existed at that time, and this idea thus marked the advent of what are now called armoured personnel carriers. Carriers were made on the spot from extra M7 Priest self-propelled guns by removing the guns and welding steel plates across the gaps this left in the armour. These modified tanks were entitled "Kangaroos" partially after the codename of the Army Workshops Detachment that produced them, and partially because of the idea that infantry would be carried in the belly of the tank as safely as a young kangaroo in its mother's pouch.