Welkin high-altitude fighter and some later Spitfire and de Havilland Mosquito variants. The odd-numbered mark drove a blower for cockpit pressurising. Merlin 130/131 ; redesigned "slimline" versions for the de Havilland Hornet. Engine design modified to decrease frontal area to a minimum and was the first Merlin series to use down-draught induction systems. Coolant pump moved from the bottom of the engine to the starboard side. Two-speed, two-stage supercharger and S.U. injection carburettor. Corliss throttle. Maximum boost was gauge; or an absolute pressure of 270 kPa or 2.7 atm). On the Hornet the Merlin 130 was fitted in the port nacelle: the Merlin 131, fitted in the starboard nacelle, was converted to a "reverse" or left-hand tractor engine using an additional idler gear in the reduction gear casing. Merlin 133/134 ; derated for use at low altitude 130/131 variants used in Sea Hornet F. Mk. 20, N.F. Mk. 21 and P.R. Mk. 22. Maximum boost was lowered to +18 psi gauge (230 kPa or 2.2 atm absolute). Merlin 266 (RM 10SM) The prefix "2" indicates engines built by Packard, otherwise as Merlin 66, optimised for low-altitude operation. Fitted to the Spitfire Mk.XVI. Merlin 620 continuous cruising using 2,650 rpm at +9 psi boost (62 kPa gauge; or an absolute pressure of 165 kPa or 1.6 atm); capable of emergency rating of at 3,000 rpm using +20 psi boost (138 kPa gauge; or an absolute pressure of 241 kPa or 2.4 atm); civilian engine developed from Merlin 102; two-stage supercharger optimised for medium altitudes, and used an S.U. injection carburettor. "Universal Power Plant" (UPP) standardised annular radiator installation development of that used on Lancaster VI and Avro Lincoln. The Merlin 620–621 series was designed to operate in the severe climatic conditions encountered on Canadian and long-range North Atlantic air routes. Used in Avro Tudor, Avro York, and the Canadair North Star. Applications In chronological order, the first operational aircraft powered by the Merlin to enter service were the Fairey Battle, Hawker Hurricane, and Supermarine Spitfire. Although the engine is most closely associated with the Spitfire, the four-engined Avro Lancaster was the most numerous application, followed by the twin-engined de Havilland Mosquito. List from Lumsden 2003 Armstrong Whitworth Whitley Avro Athena Avro Lancaster Avro Lancastrian Avro Lincoln Avro Manchester III Avro Tudor Avro York Boulton Paul Balliol and Sea Balliol Boulton Paul Defiant Bristol Beaufighter II CAC CA-18 Mark 23 Mustang Canadair