the Seafires. The Seafire F Mk III was the first true carrier adaptation of the Spitfire design. It was developed from the Seafire Mk IIc, but incorporated manually folding wings allowing more of these aircraft to be spotted on deck or in the hangars below. Supermarine devised a system of two straight chordwise folds; a break was introduced immediately outboard of the wheel-wells from which the wing hinged upwards and slightly angled towards the fuselage. A second hinge at each wingtip join allowed the tips to fold down (when the wings were folded the wingtips were folded outwards). This version used the more powerful Merlin 55 (F Mk III and FR Mk III) or Merlin 55M (L Mk III), driving the same four-bladed propeller unit used by the IIc series; the Merlin 55M was another version of the Merlin for maximum performance at low altitude. Other modifications that were made on the Spitfire made their way to the Seafire as well including a slim Aero-Vee air filter and six-stack ejector type exhausts. The shorter barrelled, lightweight Hispano Mk V cannon were introduced during production as were overload fuel tank fittings in the wings This Mark was built in larger numbers than any other Seafire variant; of the 1,220 manufactured Westland built 870 and Cunliffe Owen 350. In 1947 12 Mk IIIs were stripped of their naval equipment by Supermarine and delivered to the Irish Air Corps. After the Mk III series, the next Seafire variant to appear was the Seafire F Mk XV, which was powered by a Griffon VI – single-stage supercharger, rated at 1,850 hp (1,379 kW) at 2,000 ft (610 m) driving a 10 ft 5 in Rotol propeller. Designed in response to Specification N.4/43 this appeared to be a naval Spitfire F Mk XII; in reality the Mk XV was an amalgamation of a strengthened Seafire III airframe and wings with the wing fuel tanks, retractable tailwheel, larger elevators and broad-chord "pointed" rudder of the Spitfire VIII. The engine cowling was different from that of the Spitfire XII series, being secured with a larger number of fasteners and lacking the acorn shaped blister behind the spinner. The final 30 Mk XVs were built with the blown "teardrop" cockpit canopy and cut down rear fuselage introduced on the Spitfire Mk XVI. On the first 50 aircraft manufactured by Cunliffe-Owen a heavier, strengthened A-frame arrestor hook was fitted