The first version, the Gladiator Mk I, was delivered from July 1936, becoming operational in January 1937. The Mk II soon followed, the main differences being a slightly more powerful Mercury VIIIAS engine with Hobson mixture control boxes and a partly automatic boost control carburettor, driving a Fairey fixed-pitch three-blade metal propeller, instead of the two-blade wooden one of the Mark I. All MK II Gladiators also carried Browning 0.303-inch machine guns (licence-manufactured by the BSA company in Birmingham) in place of the Vickers-Lewis combination of the MK I. A modified Mk II, the Sea Gladiator, was developed for the Fleet Air Arm (FAA), with an arrestor hook, catapult attachment points, a strengthened airframe and an underbelly fairing for a dinghy lifeboat, all for operations aboard aircraft carriers.[11][12] Of the 98 aircraft built as, or converted to, Sea Gladiators, 54 were still in service by the outbreak of the Second World War.[11]