The Tempest fleet was built up to over 100 aircraft by September, and during the short summer nights the Tempests shared defensive duty with twin-engined de Havilland Mosquitos. Specially modified Republic P-47M Thunderbolts were also pressed into service against the V-1s; they had boosted engines (2,800 hp) and had half their machine guns and half their fuel tanks, all external fittings and all their armour plate removed to reduce weight. In addition, North American P-51 Mustangs and Griffon-engined Supermarine Spitfire Mk XIVs were tuned to make them fast enough, At night airborne radar was not needed, as the V-1 engine could be heard from away or more and the exhaust plume was visible from a long distance. Wing Commander Roland Beamont had the 20 mm cannon on his Tempest adjusted to converge at ahead. This was so successful that all other aircraft in 150 Wing were thus modified.