Supermarine type 443 Spitfire Mk.IV (DP845): First with the Griffon

nathanclawfish · August 17, 2025, 5:10pm

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              Supermarine type 443 Spitfire Mk.IV (DP845)

Design and Service History:
Specification F.4/41

In December of 1939, the Supermarine company produced a brochure that toyed with the idea of converting a Spitfire to use the Rolls-Royce Griffon engine used in their previous S.6B racing seaplane. Their initial projections were a speed of over 400mph at 18,500ft, though issues with the development of the Griffon had kept it from being considered a viable powerplant for the Spitfire until now. Intrigued by the powerplant the Air Ministry tailored a specific specification to test the aircraft in 1940, as the Merlin-powered Spitfire had already proven itself in combat against the Germans in both France and the Battle of Britain by this point.

The result of this specification was the ordering of one Aircraft, DP845, under the service designation of the Spitfire Mk.IV. DP845 was powered by a single 1,735 hp (1,293 kW) turbocharged Griffon IIB engine, which was around a third larger than the normal Merlin, requiring the engine cowling to be modified to accommodate the bulkier 37-litre engine. This additional weight also required the airframe to be modified with stronger main longerons, along with an increase in the size of both the radiator and oil cooler, though the Mk.IV retained the asymmetrical underwing configuration of the Merlin marks. The Griffon also had a lower thrust-line than the Merlin, requiring it to be set with 2 degrees of downthrust. These changes resulted in the nose of the aircraft nose to be heavily changed, creating the blisters over the cylinder heads that would be found in the later war Griffon Spitfires. The Griffon was also fitted with a 10 ft 5 in four-blade Rotol propeller spinning to the left, though from aside from the changes to the front of the aircraft, the Mk.IV was structurally similar to the Merlin-powered Mk.III.

During initial testing, the Mk.IV had an unarmed D-type wing, where it clocked an impressive performance of 445 mph (715 km/h) at 25,000 feet and 483 mph in a dive, during test flights in November of 1941. With that impressive performance, Supermarine then proposed a fighter configuration of six 20mm Hispano II cannons, using the same configuration as the contemporary competing MB.3 design, giving it an impressive 200 rounds per gun. This mockup was tested and achieved a top speed of 423mph. Unfortunately, this configuration would not bear fruit, and the Six-cannon armament would be removed and reverted to the more conventional D-type wing armament in 1942 when the Aircraft was renamed to the Mk.XX, to prevent confusion with the PR type of photo recce Spitfire. The Mk.IV aircraft would continue to serve as a Testbed for Griffon engine testing, changing designation once more to Mk.XII, and the knowledge gained would be used to produce the later war Griffon Spitfires, even if the Mk.IV would remain a single if historically significant example.

Aircraft Specification:

General characteristics

Crew: 1
Length: 32 ft 8 in (9.96 m)
Wingspan: 36 ft 10 in (11.23 m)
Height: 10 ft 0 in (3.05 m)
Wing area: 242.1 sq ft (22.49 m2)
combat weight: 7415lb
Powerplant: 1 x 1,735 hp (1,293 kW) supercharged Rolls-Royce Griffon RG 25M IIB engine
Propeller: four blade Rotol propeller

Performance:

Maximum speed: 397 m.p.h. at 17,800 ft.

Rate of climb:
Max. rate of climb in M.S. supercharger gear 3760 ft/min. at 2,600 ft.
Max. rate of climb in F.S. supercharger gear 2760 ft/min. at 15,300 ft.

Service ceiling (100 ft/min) 39,000 ft.
Time to 10,000 ft. 2.95
Time to 20,000 ft. 6.7
Time to 30,000 ft. 12.95
Time to 39,000 ft. 35.0

Armament

Guns: 6 x 20 mm Hispano Mk II (200 rounds per gun)