later with Lewis machine guns.) Other modifications included a cooling system mounted in a chin radiator housing. There was no forward firing armament and dive brakes were added to the wings. Projected speed 315 mph (507 km/h) at 15,000 ft (4,572 m). Supermarine 312: This was the basic Spitfire Mk I adapted to take four 20 mm Oerlikon cannon mounted in modified wings. The radiator and oil cooler were moved from under the wing to a duct under the fuselage. This was R J Mitchell's last design before his death in 1937. Supermarine 324, 325 and 327: These designs were for twin-engined fighters which used the same construction techniques and elliptical wing as the Spitfire. All three used tricycle undercarriage with the primary engine being a Merlin with an alternative being the Bristol Taurus. The 324 and 325 were intended to carry an armament of 12 .303 calibre Brownings in groups of six in each outer wing, while the 327 had the armament changed to six 20 mm Hispanos mounted in the wing roots. The 324 and 327 had conventional tractor engines, while the 325 had a pusher engine. Griffon engine variants The early Spitfire variants powered by the Rolls-Royce Griffon were adaptations of Mk Vc (early Mk XII) or Mark VIII (late Mk XII and Mk XIV) airframes. The later Griffon-engined Spitfire variants embodied new wings, tail units and undercarriages and were very different from any of the earlier Spitfire marks. Griffon-engined variants are described in a separate article. Production After the destruction of the main Itchen and Woolston works by the Luftwaffe in September 1940, all Supermarine manufactured Spitfires were built in a number of "Shadow Factories"; by the end of the war there were ten main factories and several smaller workshops which built many of the components. A more detailed explanation can be found in Supermarine Spitfire. The main Castle Bromwich factory was also aided by a smaller number of the shadow factories. The breakdown of production figures is taken from Air International 1985, p. 187. Information as to when the first production aircraft emerged is from the serial number lists provided in Morgan and Shacklady 2000. Because the first of the Mk IXs were converted from Mk Vcs the first true production Mk IX is listed by serial Number. See also References Notes Citations Bibliography Air Ministry. Pilot's Notes for Spitfire Mark F.VII – Merlin 64