What-if: Siamese Supermarine- The Twin Spitfire

June 29, 2012

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Initially intended as a very long-range escort fighter, the Twin Spitfire was designed to escort ‘Tiger Force’ Avro Lincoln bombers to Japan, missions beyond the range of any conventional RAF fighter. It was also seen as an alternative to the de Havilland Hornet should that aircraft prove unsatisfactory for its intended role in an ‘island-hopping’ campaign in the Pacific theatre.

Supermarine’s design team under Joe Smith developed a remarkably simple conversion consisting of two standard late production Spitfire Mk 22 fuselages and wings joined by a constant chord centre section and tailplane and with the cockpit removed from the right hand fuselage. Unlike its American counterpart, the P-82 Twin Mustang, the Twin Spitfire was a single seat aircraft, reflecting a peculiar British meanness with personnel and maximisation of offensive potential. The absence of the second cockpit and associated equipment made for a very great increase in fuel capacity and the range capability of the new aircraft was unprecedented. When external fuel tanks were added (the wings were equipped for drop tanks) the aircraft’s endurance effectively exceeded that of the average pilot.

Performance

With double the available power of a standard late-model Spitfire but less drag and lighter weight the performance of the new aircraft was outstanding. Maximum speed was 495 mph at 21,000 feet and the rate of climb and acceleration were similarly impressive. Although agility was not in the same league as the standard Spitfire, the aircraft was considered nimble for its size. A less desirable quality was the amount of torque generated by the two Griffons. With less wing area per engine relative to a standard Spitfire; the Twin Spitfire was infamous for swing on take off. Both the F-82 and the Hornet were equipped with ‘handed’ engines to negate torque effects but the Twin Spitfire was never so-equipped and pilots were required to apply full opposite rudder (even with the larger vertical surfaces developed for the Spiteful) and refrain from using full throttle until the aircraft was safely in the air.

Armament

Armament was, surprisingly, reduced in comparison to the Mk 22 Spitfire. Three 20mm cannon were mounted in the centre section of the wing, it being considered that the concentration of these weapons on the centre line of the aircraft increased the effectiveness over the standard four cannon dispersed outboard in the wings. This also allowed for a useful increase in ammunition capacity for each weapon. Later marks were developed to carry underwing ordnance for the strike role.

Operational History

The atomic bombing of Nagasaki and Hiroshima occurred as the first two Twin Spitfire squadrons were working up. Tiger Force was never deployed and the aircraft did not see operational service during World War Two. Orders for the type were slashed, though its relative ease of production due to the large levels of commonality with the Spitfire combined with the obvious merits of its performance (the aircraft was superior in speed, range and disposable load to the Gloster Meteor) meant that production did go ahead though in relatively modest numbers. The first Twin Spitfire F.Mk 1 squadron, was declared operational on the 1st of December 1945 and was deployed to Germany as part of the occupation forces in the spring of 1946, two more squadrons working up on the type throughout that year. Notwithstanding its handling quirks, the aircraft was generally popular with pilots as its blistering performance made it more or less the most potent aircraft in service in the immediate post war era. It is said that ex-Beaufighter pilots were particularly fond of it as the handling problems of both aircraft were similar but the Twin Spitfire’s levels of performance and agility were markedly superior.

Later marks adapted for the night fighter, ground attack and reconnaissance roles were speedily developed and produced.

An early problem with regard to the operational employment of the aircraft was identified almost as soon as it entered service. The pilot, sat in the left hand fuselage, had a largely unobstructed view to the left but his view to the right was severely compromised by the second fuselage and broad chord centre section of the aircraft. A few individual aircraft were modified at unit level to swap the fuselages and produce a ‘right hand drive’ version, which would invariably be detailed to fly on the right flank of any formation. Eventually right handed Twin Spitfires entered series production alongside their left handed brethren, though they were always something of a rarity. Similarly aircraft with a cockpit in both fuselages were produced, allowing for a radar operator to be carried in the Night Fighter version, a student in the training variant, and a winch operator for the target tug.

 Korea

Seeking a presence for itself over Korea during the escalating conflict, the RAF deployed a squadron of Twin Spitfire FB Mk 2s to Kimpo airfield (shared with RAAF Meteors) in 1951. The spectacular range and loitering capability of the aircraft was intensely attractive for close air support purposes and though no longer competitive in pure speed terms when compared to the latest jet fighters, the Twin Spitfire could still compare fairly favourably with the F-80 Shooting Star and was expected to be able to outmaneouvre any North Korean fighters that might be encountered. As it turned out this was to be the Twin Spitfire’s moment of glory. On the 4th of August 1952, Twin Spitfires dove on two Mig-15s and destroyed them both. A fortnight later they repeated the feat and the Twin Spitfire became one of the very few piston engined types to destroy a jet fighter in air to air combat.

Later Service 

For most of its operational life the Twin Spitfire was regarded as a tactical aircraft for strike and ground attack tasks. It operated in concert with Hornets over Malaya and appeared briefly over Suez in a single photographic sortie from a base on Cyprus. Long after this the aircraft served as a target tug, the drogue and winch being carried in a large fairing under the centre section. A few drone controller aircraft were in use until 1962.

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Variants

Supermarine Type 493:   Prototype, 2 constructed.

Twin Spitfire F Mk 1:  Initial production version, long range escort fighter, 134 built.

Twin Spitfire F Mk 1(r):  As above but produced with cockpit in right hand fuselage, 32 built.

Twin Spitfire FB Mk 2:  Equipped for underwing ordnance and epitomised for the ground attack role, 203 built.

Twin Spitfire PR 3:

Reconnaissance version, 8 built, 15 converted from F Mk 1.

Twin Spitfire NF 4:  Night fighter, 58 built.

Twin Spitfire TF Mk 5:

Trainer variant, 35 built, 30 conversions from FB Mk 2.

Twin Spitfire TT Mk 6:

Target tug, 90 produced – all conversions from FB Mk 2.

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Written by Hush Kit Posted in Aviation, The Ultimate What-If Tagged with Spitfire