 This improvement removed the RAF's Rolls-Royce Merlin-powered fighters' drawback versus the German Messerschmitt Bf 109E machine, whose Daimler-Benz DB 601 inverted V12 powerplant had had fuel injection since 1937.During early 1941, Shilling travelled with a small team to fit the restrictors in one RAF base after another, giving priority to front-line units.By March 1941 the device had been installed throughout RAF Fighter Command.