82.5 V-1 Flying Bomb kills. The Mk XII variant was retired in September 1944. Mk XIV (type 379) The first Griffon-powered Spitfires suffered from poor high altitude performance due to having only a single stage supercharged engine. By 1943, Rolls-Royce engineers had developed a new Griffon engine, the 61 series, with a two-stage supercharger. In the end it was a slightly modified engine, the 65 series, which was used in the Mk XIV. The resulting aircraft provided a substantial performance increase over the Mk IX. Although initially based on the Mk VIII airframe, common improvements made in aircraft produced later included the cut-back fuselage and tear-drop canopies, and the E-Type wing with improved armament. The Mk XIV differed from the Mk XII in that the longer, two-stage supercharged Griffon 65, producing 2,050 hp (1,528 kW), was mounted 10 inches (25.4 cm) further forward. The top section of the engine bulkhead was angled forward, creating a distinctive change of angle to the upper cowling's rear edge. A new five bladed Rotol propeller of in diameter was used, although one prototype JF321 was fitted with a six bladed contra rotating unit. The "fishtail" design of ejector exhaust stub gave way to ones of circular section. The increased cooling requirements of the Griffon engine meant that all radiators were much bigger and the underwing housings were deeper than previous versions. The cowling fasteners were new, flush fitting "Amal" type and there were more of them. The oil tank (which had been moved from the lower cowling location of the Merlin engine variants to forward of the fuselage fuel tanks) was increased in capacity from 6 to 10 gal. To help balance the new engine, the radio equipment was moved further back in the rear fuselage and the access hatch was moved from the left fuselage side to the right. Better VHF radio equipment allowed for the aerial mast to be removed and replaced by a "whip" aerial further aft on the fuselage spine. Because the longer nose and the increased slipstream of the big five-bladed propeller a new tail unit with a taller, broader fin and a rudder of increased area was adopted. The first batch of aircraft to fly with the Griffon 60 series engines were six converted Mk VIIIs JF316 to JF321 which were called Mk VIIIG. The first one of these was flown by Jeffrey Quill on 20 January 1943,