Geoffrey Wellum describes in detail the problem he and his flight of Malta Bound Spitfires had taking off from the Aircraft Carrier. They had their crews make up wedged shaped pieces of wood and jammed them into the flaps then retracting them to hold the flaps at a desired angle. Once in the air they had to lower flaps and hope that the blocks of wood would fall away.......necessity is the mother of invention...and it worked .....