Supermarine Spitfire IX: Fourth major production fighter variant (Supermarine Type 361), combining Mk VC airframe with two-stage two-speed Merlin 60 series engine but lacking other improvements designed for (later) Supermarine Spitfire VIII. Early Merlin 60 and 61 flight-tested in Supermarine Spitfire III (from August 19, 1941) and a Supermarine Spitfire IA, followed by conversion by Rolls-Royce of two Mk VCs to Mk IX prototypes with Merlin 61s early-1942. Further 282 conversions of Mk V airframes by Rolls-Royce; production totals 5,095 by CBAF and 561 by Supermarine. Service use began June 1942 in No 64 Sqn. Early standard aircraft had 'C' wing armament, standard wing span, Merlin 61 and provision for wing and fuselage bomb racks. Later, designations used to differentiate altitude rating of engine: Supermarine Spitfire LF Mk IX with Merlin 66, Supermarine Spitfire F Mk IX with Merlin 61 or 63 and Supermarine Spitfire HF Mk IX with Merlin 70. Broad-chord, pointed-tip rudder became standard later, as did compact Aero-Vee tropical filter. Late-production CBAF Mk IXs had cut-down rear fuselage with 360-deg vision canopy, and Supermarine Spitfire IXE designation (with LF, F or HF prefix) indicated new wing armament of two 20-mm cannon and two 0.50-in (12.7-mm) machine guns. More than 50 RAF and Commonwealth squadrons flew Supermarine Spitfire IXs, primarily in European theatre, and 1,188 Mk IXs were supplied to the Soviet Union in 1943-44; at least one Mk IX was modified in Russia to two-seat training configuration. A small number of Supermarine Spitfire IXs supplemented Mk Vs in USAAF service in Twelfth Air Force.
Supermarine Spitfire XVI: CBAF production of 1,054 Supermarine Spitfires similar to LF Mk IX but with US Packard-built Merlin 226 engine. Initially with 'C' wing armament, later with 'E' wing, broad-chord rudder and cut-down rear fuselage, most operated with clipped wings and all designated Supermarine Spitfire LF Mk XVI regardless of configuration. Deliveries began October 1944 and service use from November onwards, particularly by four RAF squadrons attacking V-2 sites with bombs.