The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries during and after the Second World War. The Spitfire was built in many variants, using several wing configurations, and was produced in greater numbers than any other British aircraft. It was also the only British fighter to be in continuous production throughout the war. The Spitfire continues to be a popular aircraft, with approximately 55 Spitfires being airworthy, while many more are static exhibits in aviation museums all over the world.
The Spitfire was designed as a short-range, high-performance interceptor aircraft by R. J. Mitchell, chief designer at Supermarine Aviation Works (which operated as a subsidiary of Vickers-Armstrong from 1928). In accordance with its role as an interceptor, Mitchell designed the Spitfire's distinctive elliptical wing to have the thinnest possible cross-section; this thin wing enabled the Spitfire to have a higher top speed than several contemporary fighters, including the Hawker Hurricane. Mitchell continued to refine the design until his death from cancer in 1937, whereupon his colleague Joseph Smith took over as chief designer, overseeing the development of the Spitfire through its multitude of variants.
During the Battle of Britain (July–October 1940), the Spitfire was perceived by the public to be the RAF fighter, though the more numerous Hawker Hurricane shouldered a greater proportion of the burden against the Luftwaffe. However, because of its higher performance, Spitfire units had a lower attrition rate and a higher victory-to-loss ratio than those flying Hurricanes.
After the Battle of Britain, the Spitfire superseded the Hurricane to become the backbone of RAF Fighter Command, and saw action in the European, Mediterranean, Pacific and the South-East Asian theatres. Much loved by its pilots, the Spitfire served in several roles, including interceptor, photo-reconnaissance, fighter-bomber and trainer, and it continued to serve in these roles until the 1950s. The Seafire was a carrier-based adaptation of the Spitfire which served in the Fleet Air Arm from 1942 through to the mid-1950s. Although the original airframe was designed to be powered by a Rolls-Royce Merlin engine producing 1,030 hp (768 kW), it was strong enough and adaptable enough to use increasingly powerful Merlin and, in later marks, Rolls-Royce Griffon engines producing up to 2,340 hp (1,745 kW); as a consequence of this the Spitfire's performance and capabilities improved, sometimes dramatically, over the course of its life.
In 1936, before the first flight of the prototype, the Air Ministry placed an order for 310 Spitfires. However, in spite of the promises made by the Chairman of Vickers-Armstrongs (the parent company of Supermarine) that the company would be able to deliver Spitfire at a rate of five a week, it soon became clear that this would not happen. In 1936 the Supermarine company employed 500 people and was already engaged in fulfilling orders for 48 Walrus amphibian reconnaissance aircraft and 17 Stranraer patrol flying boats. In addition the small design staff, which would have to draught the blueprints for the production aircraft, was already working at full stretch. Although it was obvious that most of the work would have to be sub-contracted to outside sources, the Vickers-Armstrongs board was reluctant to allow this to happen. When other companies were able to start building Spitfire components there were continual delays because either parts provided to them would not fit, or the blueprints were inadequate; the sub-contractors themselves faced numerous problems building components which in many cases were more advanced and complicated than anything they had faced before.
As a consequence of the delays, the RAF received the first two Spitfires off the production line in July 1938, while the first Spitfire to enter squadron service was received by 19 Squadron in early August. For a time the future of the Spitfire was in serious doubt, with the Air Ministry suggesting that the programme be abandoned and that Supermarine change over to building the Bristol Beaufighter under licence. The managements of Supermarine and Vickers were eventually able to convince the Air Ministry that production would be sorted out and, in 1938, an order was placed with Morris Motors LImited for an additional 1,000 Spitfires to be built at huge new factory which was to be built at Castle Bromwich. This was followed in 1939 by an order for another 200 from Woolston and, only a few months later, another 450. This brought the total to 2,160, making it one of the largest orders in RAF history. Over the next three years a large number of modifications were made, most as a result of wartime experience.
Early in the Spitfire's operational life a major problem became apparent; at altitudes above about 15,000 ft (4,572 m), any condensation could freeze in the guns. Because of this the system of gun heating first fitted to K5054 was introduced on the 61st production Mk I. At the outset of World War II, the flash-hiders on the gun muzzles were removed and the practice of sealing the gun ports with fabric patches was instituted. The patches kept the gun barrels free of dirt and debris and allowed the hot air to heat the guns more efficiently. Early production aircraft were fitted with a ring and bead gunsight, although provision had been made for a reflector sight to be fitted once one had been selected. In July 1938, the Barr and Stroud GM 2 was selected as the standard RAF reflector gunsight and was fitted to the Spitfire from late 1938. These first production Mk Is were able to reach a maximum speed of 362 mph (583 km/h) at 18,500 ft (5,600 m), with a maximum rate of climb of 2,490 ft/min at 10,000 ft (3,000 m). The service ceiling (where the climb rate drops to 100 ft/min) was 31,900 ft (9,700 m).
All Merlin I to III series engines relied on external electric power to start; a well known sight on RAF fighter airfields was the "trolley acc" (trolley accumulator) which was a set of powerful batteries which could be wheeled up to aircraft. The lead from the "Trolley Acc" was plugged into a small recess on the starboard side cowling of the Spitfire. On Supermarine-built aircraft a small brass instruction plate was secured to the side cowling, just beneath the starboard exhausts.
The early Mk Is were powered by the 1,030 hp (768 kW) Merlin Mk II engine driving an Aero-Products "Watts" 10 ft 8 in (3.3 m) diameter two-blade wooden fixed-pitch propeller, weighing 83 lb (38 kg). From the 78th production airframe, the Aero Products propeller was replaced by a 350 lb (183 kg) de Havilland 9 ft 8 in (2.97 m) diameter, three-bladed, two-position, metal propeller, which greatly improved take-off performance, maximum speed and the service ceiling. From the 175th production aircraft, the Merlin Mk III, with a "universal" propeller shaft able to take a de Havilland or Rotol propeller, was fitted. Following complaints from pilots a new form of "blown" canopy was manufactured and started replacing the original "flat" version in early 1939. This canopy improved headroom and enabled better vision laterally, and to the rear. At the same time the manual hand-pump for operating the undercarriage was replaced by a hydraulic system driven by a pump mounted in the engine bay. Spitfire Is incorporating these modifications were able to achieve a maximum speed of 367 mph (591 km/h) at 18,600 ft (5,700 m), with a maximum rate of climb of 2,150 ft/min at 10,000 ft (3,000 m). The service ceiling was 34,400 ft (10,500 m).
A voltage regulator under a black, cylindrical cover was mounted low on the back of frame 11, directly behind the pilot's seat:starting in the N30xx series this was repositioned higher, appearing low in the rear transparency. From N32xx the regulator was mounted directly behind the pilot's headrest on frame 11. Other changes were made later in 1939 when a simplified design of pitot tube was introduced and the "rod" aerial mast was replaced by a streamlined, tapered design. To improve protection for the pilot and fuel tanks a thick laminated glass bulletproof plate was fitted to the curved, one piece windscreen and a 3 mm thick cover of light alloy, capable of deflecting small calibre rounds, was fitted over the top of the two fuel tanks. From about mid-1940, 73 pounds (33 kg) of armoured steel plating was provided in the form of head and back protection on the seat bulkhead and covering the forward face of the glycol header tank. In addition, the lower petrol tank was fitted with a fire resistant covering called "Linatex", which was later replaced with a layer of self-sealing rubber.
In June 1940 de Havilland began manufacturing a kit to convert their two pitch propeller unit to a constant speed propeller. Although this propeller was a great deal heavier than the earlier types (500 lb (227 kg) compared with 350 lb (183 kg)) it provided another substantial improvement in take-off distance and climb rate. Starting on 24 June de Havilland engineers began fitting all Spitfires with these units and by 16 August every Spitfire and Hurricane had been modified. "Two step" rudder pedals were fitted to all frontline Spitfires; these allowed the pilot to lift his feet and legs higher during combat, improving his "blackout" threshold and allowing him to pull tighter sustained turns.
Another modification was the small rear view mirror which was added to the top of the windscreen: an early "shrouded" style was later replaced by a simplified, rectangular, adjustable type.
Starting in September 1940, IFF equipment was installed. This weighed about 40 lb (18 kg) and could be identified by wire aerials strung between the tailplane tips and rear fuselage. Although the added weight and the aerials reduced maximum speed by about two mph (three km/h), it allowed the aircraft to be identified as "friendly" on radar: lack of such equipment was a factor leading to the Battle of Barking Creek. At about the same time new VHF T/R Type 1133 radios started replacing the HF TR9 sets. These had first been fitted to Spitfires of 54 and 66 Squadrons in May 1940, but ensuing production delays meant the bulk of Spitfires and Hurricanes were not fitted for another five months. The pilots enjoyed a much clearer reception which was a big advantage with the adoption of Wing formations throughout the RAF in 1941. The new installation meant that the wire running between the aerial mast and rudder could be removed, as could the triangular "prong" on the mast.
Weight increases and aerodynamic changes led to later Spitfire Is having a lower maximum speed than the early production versions. This was more than offset by the improvements in take-off distance and rate of climb brought about by the constant speed propeller units. During the Battle of Britain Spitfire Is equipped with constant-speed propellers had a maximum speed of 353 mph (568 km/h) at 20,000 ft (6,100 m), with a maximum rate of climb of 2,895 ft/min at 10,000 ft (3,000 m).
Although the Merlin III engine of Spitfire Is had a power rating of 1,030 hp (768 kW), supplies of 100 octane fuel from the United States started reaching Britain in early 1940. This meant that an "emergency boost" of +12 pounds per square inch was available for five minutes, with pilots able to call on 1,310 hp (977 kW) at 3,000 rpm at 9,000 feet (2,743 m). This boosted the maximum speed by 25 mph (40 km/h) at sea level and 34 mph (55 km/h) at 10,000 ft (3,000 m) and improved the climbing performance between sea level and full throttle height. The extra boost wasn't damaging as long as the limitations set forth in the pilot's notes were followed. As a precaution if the pilot had resorted to emergency boost, he had to report this on landing and it had to be noted in the engine log book. There was a wire 'gate' fitted, which the pilot had to break to set the engine to emergency power, this acted as an indicator that emergency power had been used and would be replaced by mechanics on the ground. The extra boost was also available for the Merlin XII fitted to the Spitfire II.
Late in 1940, a Martin-Baker designed quick-release mechanism began to be retroactively fitted to all Spitfires. The system employed unlocking pins, actuated by cables operated by the pilot pulling a small, red rubber ball mounted on the canopy arch. When freed, the canopy was taken away by the slipstream. One of the most important modifications to the Spitfire was to replace the machine gun armament with wing mounted Hispano 20 mm cannon. In December 1938, Joseph Smith was instructed to prepare a scheme to equip a Spitfire with a single Hispano mounted under each wing. Smith objected to the idea and designed an installation in which the cannon were mounted on their sides within the wing, with only small external blisters on the upper and lower wing surfaces covering the 60 round drum magazine. The first Spitfire armed with a single Hispano in each wing was L1007 which was posted to Drem in January 1940 for squadron trials. On 13 January, this aircraft, piloted by Plt Off Proudman of 602 Squadron took part in an engagement when a Heinkel He 111 was shot down. Soon after this Supermarine was contracted to convert 30 Spitfires to take the cannon armed wing; 19 Squadron received the first of these in June 1940 and by 16 August, 24 cannon armed Spitfires had been delivered. These were known as the Mk IB: Mk Is armed with eight Brownings were retrospectively called the Mk Ia. With the early cannon installation, jamming was a serious problem. In one engagement, only two of the 12 aircraft had been able to fire off all of their ammunition. Further cannon-armed Spitfires, with improvements to the cannon mounts, were later issued to 92 Squadron, but due to the limited magazine capacity it was eventually decided the best armament mix was two cannon and four machine guns (most of these were later converted to the first Mk VBs).
From November 1940, a decision was taken that Supermarine would start producing light-alloy covered ailerons which would replace the original fabric covered versions. However, seven months after the decision was taken to install them on all marks, Spitfires were still being delivered with the original fabric covered ailerons. From May 1941 metal ailerons were fitted to all Spitfires coming off the production lines
The Spitfires with the Single Stage Merlin engines used four different wing types, A through to D which had the same dimensions and plan but different internal arrangements of armament and fuel tanks. All Mk Is, IIs, and Vs and their derivatives had small, rectangular undercarriage indicator pins which projected at an angle from the upper wing surfaces when the undercarriage legs were locked down. These supplemented lights on the instrument panel. All of these variants used Dunlop AH2061 mainwheels which had five openings. The fixed, castering tailwheels were Dunlop AH2184s.
Starting with the Mk V some Spitfires had their rounded wingtips replaced by shorter, squared-off fairings to improve low-altitude performance and enhance the roll rate. These are sometimes referred to as "L.F" versions, e.g. L.F. Mk. VB: this designation referred to the low-altitude versions of the Rolls-Royce Merlin with the "cropped" supercharger impellers (known as Merlin 45M, 50M or 55M). While many "L.F" Spitfires had the "clipped" wings, a number did not.