Vickers Supermarine
 Spitfire Mk IX b

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. Max speed, 408 mph (657 km/h) at 25,000ft (7,620 m). Time to 20,000ft (6,100 m), 5.7 min. Initial climb, 3,950 ft/min (20.1 mlsec). Service ceiling, 43,000 ft (13,106 m). Range, internal fuel, 434 mis (698 km). Empty weight, 5,634 Ib (2,556 kg). Gross weight, 9,500 Ib (4,309 kg). Span, 36 ft 10 in (11.23 m) or 32 ft 9 in (9.80 m). Length, 31 ft 1 in (9.47 m). Wing area, 242 sq ft (22.48m2).
 

Spitfire Mark IX EN398 flown by the RAF's highest scoring ace, J.E. 'Johnnie' Johnson - reproduced with thanks from Daniel March 'British Warplanes of World War II' (Grange Books, 2000)

InJuly 1942 a Spitfire IX was flown in a comparative trial against a Focke-Wulf 190A which had fallen into British hands when its pilot landed by mistake at Pembrey RAF base at  in Wales.  The trial showed that there was a remarkable similarity in performance. The following are extracts from the official report.

TheFW190 was compared with a fully operational Spitfire IX for speed and manoeuvrability at heights up to 25,000 feet [7620 metres]. 

At most heights the Spitfire IX is slightly superior in speed to the FW190 - 
the approximate differences in speed are as follows:

At 2,000 ft [610 m] the FW 190 is 7-8 mph [11-13 km/hr] faster than the Spitfire 
At 5,000 ft [1524 m] the FW 190 and the Spitfire are approximately the same
At 8,000 ft [2440 m] the Spitfire IX is 8 mph [13 km/hr] faster than the FW 190
At 15,000 ft [4573 m] the Spitfire IX is 5 mph [8 km/hr] faster than the FW 190
At 18,000 ft [5488 m] the FW 190 is 3 mph [5 km/hr] faster than the Spitfire IX
At 21,000 ft  [6400 m] the FW 190 and the Spitfire are approximately the same
At 25,000 ft [7622 m] the Spitfire IX is 5-7 mph [8-11 km/hr] faster than the FW 190

Climb:During comparative climbs at various heights up to 23,000 feet [7012 metres], with both aircraft flying under maximum continuous climbing conditions, little difference was found between the two aircraft although on the whole the Spitfire was slightly better.

Above 22,000 feet [6707 m] the climb of the FW 190 is falling off rapidly, whereas the climb of the Spitfire IX is increasing.

Dive:  The FW 190 is faster than the Spitfire IX in a dive, particularly during the initial stage. This superiority is not as marked as with the Spitfire VB.

Manoeuvrability: The  FW 190 is more manoeuvrable than the Spitfire IX except in turning circles. 
The superior rate of roll of the FW 190 enabled it to avoid the Spitfire IX by turning over into a diving turn in the opposite direction.

The Spitfire IX's worst heights for fighting the FW 190 were  between 18,000 and 22,000 feet [5486-6707m] and also below 3,000 feet [914m].

The initial acceleration of the FW 190 is better than that of the Spitfire IX under all conditions of flight, except in level flight at altitudes where the Spitfire has a speed advantage.

The general impression of the pilots involved in the trials is that the Spitfire Mark IX compares well with the FW 190.  Providing the Spitfire IX has the initiative, it undoubtedly stands a good chance of shooting down the FW 190.

Spitfire LF IXE ML417 (preserved) in markings of 443 'Hornet' Squadron RCAF - reproduced with thanks from 'Spitfire - Flying Legend' by J Dibbs & T Holmes (Osprey Aviation, 1996