 After a study concluded that the thousands of aircraft involved in the invasion would saturate and break down the IFF system, the marking scheme was approved on May 17, 1944, by Air Chief Marshal Sir Trafford Leigh-Mallory, commanding the Allied Expeditionary Air Force.A small-scale test exercise was flown over the OVERLORD invasion fleet on June 1, to familiarise the ships' crews with the markings, but for security reasons, orders to paint the stripes were not issued to the troop carrier units until June 3 and to the fighter and bomber units until June 4.Stripes were applied to fighters, photo-reconnaissance aircraft, troop carriers, twin-engined medium and light bombers, and some special duty aircraft.