Caption: RAF fighters rehearse at Northolt for Empire Air Day. Royal Air Force fighter and bomber pilots rehearsed at Northolt the flying display they will give at the station on Empire Air Day, 29 May, when the aerodrome, in common with a 52 other RAF units, will be open for public inspection. Photo shows, Gloster Gauntlet Mk II of number 111 Squadron flying over a machine gunner in a Hawker Demon of number 23 (F) Squadron at Northolt.