Supermarine Spitfire
Spitfire LF Mk IX, MH434, flown by Ray Hanna in 2005. This aircraft shot down a Fw 190 in 1943 while serving with 222 Squadron RAF.
Role	Fighter / Photo-reconnaissance aircraft
Manufacturer	Supermarine
Designer	R. J. Mitchell
First flight	5 March 1936[1]
Introduction	4 August 1938[1]
Retired	1961 Irish Air Corps[2]
Primary user	Royal Air Force
Produced	1938–1948
Number built	20,351[3]
Unit cost	£12,604 (Estonian order for 12 Spitfires in 1939)[nb 1].[4]
Variants	Supermarine Seafire Supermarine Spiteful

The Supermarine Spitfire was a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s. It was produced in greater numbers than any other British aircraft and was the only British fighter in production throughout the war.^[5]

The Spitfire was designed as a short-range, high-performance interceptor aircraft^[6] by R. J. Mitchell, chief designer at Supermarine Aviation Works (which operated as a subsidiary of Vickers-Armstrong since 1928). Mitchell continued to refine the design until his death from cancer in 1937, whereupon his colleague Joseph Smith became chief designer.^[7] The Spitfire's elliptical wing had a thin cross-section, allowing a higher top speed than several contemporary fighters, including the Hawker Hurricane.^[8] Speed was seen as essential to carry out the mission of home defence against enemy bombers.^[6]

During the Battle of Britain (July-October 1940), the Spitfire was perceived by the public as the RAF fighter of the battle, though the more numerous Hawker Hurricane shouldered a greater proportion of the burden against the Luftwaffe. The Spitfire units had a lower attrition rate and a higher victory to loss ratio than those flying Hurricanes.^[9]

After the Battle of Britain, the Spitfire became 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, carrier-based fighter, and trainer. It was built in many variants, using several wing configurations.^[10] Although the original airframe was designed to be powered by a Rolls-Royce Merlin engine producing 1,030 hp (768 kW), it was adaptable enough to use increasingly powerful Merlin and later Rolls-Royce Griffon engines; the latter was eventually able to produce 2,035 hp (1,520  kW).^[11]

Design and development[link]

R. J. Mitchell's 1931 design to meet Air Ministry specification F7/30 for a new and modern fighter capable of 251 mph (404 km/h), the Supermarine Type 224, resulted in an open-cockpit monoplane with bulky gull-wings and a large fixed, spatted undercarriage powered by the 600 horsepower (450 kW) evaporative-cooled Rolls-Royce Goshawk engine.^[13] This made its first flight in February 1934.^[14] The Type 224 was a big disappointment to Mitchell and his design team, who immediately embarked on a series of "cleaned-up" designs, using their experience with the Schneider Trophy seaplanes as a starting point. Of the seven designs tendered to F/30, the Gloster Gladiator biplane was accepted for service.^[15]

Mitchell had already begun working on a new aircraft, designated Type 300, based on the Type 224, but with a retractable undercarriage and the wingspan reduced by 6 ft (1.8 m). The Type 300 was submitted to the Air Ministry in July 1934, but again was not accepted.^[16] The design then evolved through a number of changes, including incorporating a faired, enclosed cockpit, oxygen-breathing apparatus, smaller and thinner wings, and the newly-developed, more powerful Rolls-Royce PV-XII V-12 engine, later named the "Merlin". In November 1934, Mitchell, with the backing of Supermarine's owner, Vickers-Armstrong, started detailed design work on this refined version of the Type 300^[17] and, on 1 December 1934, the Air Ministry issued a contract AM 361140/34, providing £10,000 for the construction of Mitchell's improved F7/30 design.^[18] On 3 January 1935, the Air Ministry formalised the contract and a new Specification F10/35 was written around the aircraft.^[19]

In April 1935, the armament was changed from two .303 in (7.7 mm) Vickers machine guns in each wing to four .303 in (7.7 mm) Brownings,^[20] following a recommendation by Squadron Leader Ralph Sorley of the Operational Requirements section at the Air Ministry.^[21]

On 5 March 1936,^[22] the prototype (K5054) took off on its first flight from Eastleigh Aerodrome (later Southampton Airport). At the controls was Captain Joseph "Mutt" Summers, chief test pilot for Vickers (Aviation) Ltd., who was reported in the press as saying "Don't touch anything" on landing.^{[23][nb 2]} This eight minute flight^[21] came four months after the maiden flight of the contemporary Hurricane.^[25]

K5054 was fitted with a new propeller, and Summers flew the aircraft on 10 March 1936; during this flight the undercarriage was retracted for the first time.^[26] After the fourth flight, a new engine was fitted, and Summers left the test-flying to his assistants, Jeffrey Quill and George Pickering. They soon discovered that the Spitfire^{[nb 3][29]} was a very good aircraft, but not perfect. The rudder was over-sensitive and the top speed was just 330 mph (528 km/h), little faster than Sydney Camm's new Merlin-powered Hurricane.^[31] A new and better-shaped wooden propeller meant the Spitfire reached 348 mph (557 km/h) in level flight in mid-May, when Summers flew K5054 to RAF Martlesham Heath and handed the aircraft over to Squadron Leader Anderson of the Aeroplane & Armament Experimental Establishment (A&AEE). Here, Flight Lieutenant Humphrey Edwardes-Jones took over the prototype for the RAF.^[32] He had been given orders to fly the aircraft and then to make his report to the Air Ministry as he landed. Edwardes-Jones made a positive report; his only request was that the Spitfire be equipped with an undercarriage position indicator.^[33] A week later, on 3 June 1936, the Air Ministry placed an order for 310 Spitfires,^[34] before any formal report had been issued by the A&AEE; interim reports were later issued on a piecemeal basis.^[35]

The British public first saw the Spitfire at the RAF Hendon air-display on Saturday 27 June 1936. Although full-scale production was supposed to begin immediately, there were numerous problems which could not be overcome for some time and the first production Spitfire, K9787, did not roll off the Woolston, Southampton assembly line until mid-1938.^[1] The first and most immediate problem was that the main Supermarine factory at Woolston was already working at full capacity fulfilling orders for Walrus and Stranraer flying boats. Although outside contractors were supposed to be involved in manufacturing many important Spitfire components, especially the wings, Vickers-Armstrong (the parent company) were reluctant to see the Spitfire being manufactured by outside concerns and were slow to release the necessary blueprints and subcomponents. As a result of the delays in getting the Spitfire into full production, the Air Ministry put forward a plan that production of the Spitfire be stopped after the initial order for 310, after which Supermarine would build Bristol Beaufighters. The managements of Supermarine and Vickers were able to persuade the Air Ministry that the problems could be overcome and further orders were placed for 200 Spitfires on 24 March 1938, the two orders covering the K, L and N prefix serial numbers.^[36]

Airframe[link]

Spitfire Mk IIa P7350 of the BBMF is the only existing airworthy Spitfire that fought in the Battle of Britain.

In the mid-1930s, aviation design teams worldwide started developing a new generation of all-metal, low-wing fighter aircraft. The French Dewoitine D.520^[37] and Germany's Messerschmitt Bf 109, for example, were designed to take advantage of new techniques of monocoque construction and the availability of new high-powered, liquid-cooled, in-line aero engines. They also featured refinements such as retractable undercarriages, fully enclosed cockpits and low drag, all-metal wings (all introduced on civil airliners years before but slow to be adopted by the military, who favoured the simplicity and manoeuvrability of the biplane).^[38]

Mitchell's design aims were to create a well-balanced, high-performance bomber interceptor and fighter aircraft capable of fully exploiting the power of the Merlin engine, while being relatively easy to fly.^[39] At the time, no enemy fighters were expected to appear over Great Britain; to carry out the mission of home defence, the design was intended to climb quickly to meet enemy bombers.^[6]

The Spitfire's airframe was complex: the streamlined, semi-monocoque duralumin fuselage featured a large number of compound curves built up from a skeleton of 19 frames, starting from frame number one, immediately behind the propeller unit, to the tail unit attachment frame. The first four frames supported the glycol header tank and engine cowlings. Frame 5, to which the engine bearers were secured, supported the weight of the engine and accessories, and the loads imposed by the engine: this was a strengthened double frame which also incorporated the fireproof bulkhead and, in later versions of the Spitfire, the oil tank. This frame also tied the four main fuselage longerons to the rest of the airframe.^[40] Behind the bulkhead were five 'U' shaped half-frames which accommodated the fuel tanks and cockpit. From the eleventh frame, to which the pilot's seat and (later) armour plating was attached, to the nineteenth, which was mounted at a slight forward angle just forward of the fin, the frames were oval, each reducing slightly in size, and each incorporating several holes in order to lighten them as much as possible without weakening them. The U-shaped frame 20 was the last frame of the fuselage proper and the frame to which the tail unit was attached. Frames 21, 22 and 23 formed the fin; frame 22 incorporated the tailwheel opening and frame 23 was the rudder post. Before being attached to the main fuselage, the tail unit frames were held in a jig and the eight horizontal tail formers were riveted to them.^[41]

A combination of 14 longitudinal stringers and four main longerons attached to the frames helped form a light but rigid structure to which sheets of alclad stressed skinning were attached. The fuselage plating was 24, 20 and 18 gauge in order of thickness towards the tail, while the fin structure was completed using short longerons from frames 20 to 23, before being covered in 22 gauge plating.^[42] There was ample room for the camera equipment and additional fuel tanks which were to be fitted during the Spitfire's operational service life.^[43]

The skins of the fuselage, wings and tailplane were secured by rivets and in critical areas such as the wing forward of the main spar where an uninterrupted airflow was required, with flush rivets; the fuselage used standard dome-headed riveting. From February 1943 flush riveting was used on the fuselage, affecting all Spitfire variants.^[44] In some areas, such as at the rear of the wing, and the lower tailplane skins the top was riveted and the bottom fixed by brass screws which tapped into strips of spruce which were bolted to the lower ribs. The removable wing tips were made up of spruce formers to which the duralumin skin was secured.^[45] At first the ailerons, elevators and rudder were fabric-covered. When combat experience showed that fabric-covered ailerons were impossible to use at high speeds, fabric was replaced with a light alloy, enhancing control throughout the speed range.^[46]

Elliptical wing design[link]

The elliptical planform of a Spitfire PR.Mk.XIX is seen at a British air show in 2008. It shows the black and white Invasion stripes.

In 1934, Mitchell and the design staff decided to use a semi-elliptical wing shape to solve two conflicting requirements; the wing needed to be thin, to avoid creating too much drag, while still able to house a retractable undercarriage, plus armament and ammunition. Beverly Shenstone, the aerodynamicist on Mitchell's team, explained why that form was chosen:

The elliptical wing was decided upon quite early on. Aerodynamically it was the best for our purpose because the induced drag, that caused in producing lift, was lowest when this shape was used: the ellipse was ... theoretically a perfection ... To reduce drag we wanted the lowest possible thickness-to-chord, consistent with the necessary strength. But near the root the wing had to be thick enough to accommodate the retracted undercarriages and the guns ... Mitchell was an intensely practical man... The ellipse was simply the shape that allowed us the thinnest possible wing with room inside to carry the necessary structure and the things we wanted to cram in. And it looked nice.

—^[47]

Mitchell has sometimes been accused of copying the wing shape of the Heinkel He 70, which first flew in 1932; but as Shenstone explained "Our wing was much thinner and had quite a different section to that of the Heinkel. In any case it would have been simply asking for trouble to have copied a wing shape from an aircraft designed for an entirely different purpose."^{[48] [nb 4]}

The wing section used was from the NACA 2200 series, which had been adapted to create a thickness-to-chord ratio of 13% at the root, reducing to 9.4% at the tip.^[50] A dihedral of six degrees was adopted to give increased lateral stability.^[39]

A feature of the wing which contributed greatly to its success was an innovative spar boom design, made up of five square tubes which fitted into each other. As the wing thinned out along its span the tubes were progressively cut away in a similar fashion to a leaf spring; two of these booms were linked together by an alloy web, creating a lightweight and very strong main spar.^[51] The undercarriage legs were attached to pivot points built into the inner, rear section of the main spar and retracted outwards and slightly backwards into wells in the non-load-carrying wing structure. The resultant narrow undercarriage track was considered to be an acceptable compromise as this reduced the bending loads on the main-spar during landing.^[51]

Ahead of the spar, the thick-skinned leading edge of the wing formed a strong and rigid D-shaped box, which took most of the wing loads. At the time the wing was designed, this D-shaped leading edge was intended to house steam condensers for the evaporative cooling system intended for the PV-XII. Constant problems with the evaporative system in the Goshawk led to the adoption of a cooling system which used 100% glycol^{[nb 5]}. The radiators were housed in a new radiator-duct designed by Fredrick Meredith of the RAE at Farnborough; this used the cooling air to generate thrust, greatly reducing the net drag produced by the radiators.^[52] In turn, the leading-edge structure lost its function as a condenser, but it was later adapted to house integral fuel tanks of various sizes.^[53]

Another feature of the wing was its washout. The trailing edge of the wing twisted slightly upward along its span, the angle of incidence decreasing from +2° at its root to -½° at its tip.^[54] This caused the wing roots to stall before the tips, reducing tip-stall that could otherwise have resulted in a spin. As the wing roots started to stall, the aircraft vibrated, warning the pilot, and hence allowing even relatively inexperienced pilots to fly the aircraft to the limits of its performance.^[55] This washout was first featured in the wing of the Type 224 and became a consistent feature in subsequent designs leading to the Spitfire.^[56] The complexity of the wing design, especially the precision required to manufacture the vital spar and leading-edge structures, at first caused some major hold-ups in the production of the Spitfire. The problems increased when the work was put out to subcontractors, most of whom had never dealt with metal-structured, high-speed aircraft. By June 1939, most of these problems had been resolved, and Spitfire production was no longer held up by a lack of wings.^[57]

All of the main flight controls were originally metal structures with fabric covering.^{[nb 6]}Designers and pilots felt that having ailerons which were too heavy to move at high speed would avoid possible aileron reversal, stopping pilots throwing the aircraft around and pulling the wings off. It was also felt that air combat would take place at relatively low speed and that high-speed manoeuvring would be physically impossible.^[59] During the Battle of Britain, pilots found the ailerons of the Spitfire were far too heavy at high speeds, severely restricting lateral manoeuvres such as rolls and high speed turns, which were still a feature of air-to-air combat.^[60] Flight tests showed the fabric covering of the ailerons "ballooned" at high speeds, adversely affecting the aerodynamics. Replacing the fabric covering with light alloy dramatically improved the ailerons at high speed.^[61]

The Spitfire had detachable wing tips which were secured by two mounting points at the end of each main wing assembly: when the Spitfire took on a role as a high altitude fighter (Marks VI and VII and some early Mk VIIIs) the standard wing tips were replaced by extended, "pointed" tips which increased the wingspan from 36 ft 10 in (11.23 m) to 40 ft 2 in (12.3 m).^[62] The other wing tip variation, used by several Spitfire variants, was the "clipped" wing; the standard wing tips were replaced by wooden fairings which reduced the span to 32 ft 6 in (9.9 m)^[63] The wing tips used spruce formers for most of the internal structure with a light alloy skin attached using brass screws.^[64]

The airflow through the main radiator was controlled by pneumatic exit flaps. In early marks of Spitfire (Mk I to Mk VI) the single flap was operated manually using a lever to the left of the pilot's seat. When the two-stage Merlin was introduced in the Spitfire Mk IX the radiators were split to make room for an intercooler radiator; the radiator under the starboard wing was halved in size and the intercooler radiator housed alongside. Under the port wing a new radiator fairing housed a square oil cooler alongside of the other half-radiator unit. The two radiator flaps were now operated automatically via a thermostat.^[65]

The light alloy split flaps at the trailing edge of the wing were also pneumatically operated via a finger lever on the instrument panel.^[66] Only two positions were available; fully up or fully down (85°). The flaps were normally lowered only during the final approach and for landing, and the pilot was to retract them before taxiing.^{[nb 7][67]}

The ellipse also served as the design basis for the Spitfire’s fin and tailplane assembly, once again exploiting the shape’s favourable aerodynamic characteristics. Both the elevators and rudder were shaped so that their centre of mass was shifted forward, thus reducing control-surface flutter. The longer noses and greater propeller-wash resulting from larger engines in later models necessitated increasingly larger vertical and, later, horizontal tail surfaces to compensate for the altered aerodynamics, culminating in those of the Mk 22/24 series which were 25% larger in area than those of the Mk I.^[68][69]

Improved late wing designs[link]

As the Spitfire gained more power and was able to manoeuvre at higher speeds, the possibility that pilots would encounter aileron reversal increased, and the Supermarine design team set about redesigning the wings to counter this. The original wing design had a theoretical aileron reversal speed of 580 mph (930 km/h),^[70] which was somewhat lower than that of some contemporary fighters. The Royal Aircraft Establishment noted that, at 400 mph (640 km/h) IAS, roughly 65% of aileron effectiveness was lost, due to wing twist.^[71]

The new wing of the Spitfire F Mk 21 and its successors was designed to help alleviate this problem; the wing's stiffness was increased by 47%, and a new design of aileron using piano hinges and geared trim tabs meant that the theoretical aileron reversal speed was increased to 825 mph (1,328 km/h).^[70][72][73] Alongside of the redesigned wing Supermarine also experimented with the original wing, raising the leading edge by one inch (2.54 cm), with the hope of improving pilot view and reducing drag. This wing was tested on a modified F Mk 21, also called the F Mk 23, (sometimes referred to as "Valiant" rather than "Spitfire"). The increase in performance was minimal and this experiment was abandoned.^[74]

Supermarine developed a new laminar flow wing based on new aerofoil profiles developed by NACA in the United States, with the objective of reducing drag and improving performance. These laminar flow airfoils were the Supermarine 371-I used at the root and the 371-II used at the tip.^[75] Supermarine estimated that the new wing could give an increase in speed of 55 mph (89 km/h) over the Spitfire Mk 21.^[76] The new wing was initially fitted to a Spitfire Mk XIV; later a new fuselage was designed, with the new fighter becoming the Supermarine Spiteful.^[77]

Carburettor versus fuel injection[link]

Early in its development, the Merlin engine's lack of direct fuel injection meant that both Spitfires and Hurricanes, unlike the Bf 109E, were unable to simply nose down into a steep dive. This meant a Luftwaffe fighter could simply "bunt" into a high-power dive to escape an attack, leaving the Spitfire behind, as its fuel was forced by negative "g" out of the carburettor. RAF fighter pilots soon learnt to "half-roll" their aircraft before diving to pursue their opponents.^[78] Carburettors were adopted because, as Sir Stanley Hooker explained, it was believed that the carburettor "increased the performance of the supercharger and thereby increased the power of the engine."^[79] In March 1941, a metal diaphragm with a hole in it was fitted In the fuel line, restricting fuel flow to the maximum the engine could consume. While it did not cure the problem of the initial fuel starvation in a dive, it did reduce the more serious problem of the carburettor being flooded with fuel by the fuel pumps under negative "g". It became known as "Miss Shilling's orifice" as it was invented by Beatrice "Tilly" Shilling. Further improvements were introduced throughout the Merlin series, with Bendix-manufactured pressure carburettors, which were designed to allow fuel to flow during all flight attitudes, introduced in 1942.^[79]

Armament[link]

Due to a shortage of Brownings, which had been selected as the new standard rifle calibre machine gun for the RAF in 1934, early Spitfires were fitted with only four guns, with the other four fitted later.^[80] Early tests showed that while the guns worked perfectly on the ground and at low altitudes, they tended to freeze at high altitude, especially the outer wing guns. This was because the RAF's Brownings had been modified to fire from an open bolt; while this prevented overheating of the cordite used in British ammunition, it allowed cold air to flow through the barrel unhindered.^[81] Supermarine did not fix the problem until October 1938, when they added hot air ducts from the rear of the wing mounted radiators to the guns, and bulkheads around the gunbays to trap the hot air in the wing. Red fabric patches were doped over the gun ports to protect the guns from cold, dirt and moisture until they were fired.^[82] Even if the eight Brownings worked perfectly, pilots soon discovered that they were not sufficient to destroy larger aircraft. Combat reports showed that an average of 4,500 rounds were needed to shoot down an enemy aircraft. In November 1938, tests against armoured and unarmoured targets had already indicated that the introduction of a weapon of at least 20 mm calibre was urgently needed.^[83] A variant on the Spitfire design with four 20mm Oerlikon cannon had been tendered to specification F37/35 but the order for prototypes had gone to the Westland Whirlwind in January 1939.^[84]

In June 1939, a single Spitfire was fitted with a single drum-fed Hispano in each wing, an installation that required large blisters on the wing to cover the 60-round drum. The cannons suffered frequent stoppages, mostly because the guns were mounted on their sides to fit as much of the magazine as possible within the wing. In January 1940, P/O George Proudman flew this prototype in combat, but the starboard gun stopped after firing a single round, while the port gun fired 30 rounds before seizing.^[82] If one cannon seized, the recoil of the other threw the aircraft off aim. Nevertheless, 30 more cannon-armed Spitfires were ordered for operational trials, and they were soon known as the Mk IB, to distinguish them from the Browning-armed Mk IA, and were delivered to No. 19 Squadron beginning in June 1940. The Hispanos were found to be so unreliable that the squadron requested an exchange of its aircraft with the older Browning-armed aircraft of an operational training unit. By August, Supermarine had perfected a more reliable installation with an improved feed mechanism and four .303s in the outer wing panels. The modified fighters were then delivered to 19 Squadron.^[82]

Production[link]

In February 1936 the director of Vickers-Armstrongs, Sir Robert MacLean, guaranteed production of five aircraft a week, beginning 15 months after an order was placed. On 3 June 1936, the Air Ministry placed an order for 310 aircraft, for a price of £1,395,000.^[85] Full-scale production of the Spitfire began at Supermarine's facility in Woolston, Southampton, but it quickly became clear that the order could not be completed in the 15 months promised. Supermarine was a small company, already busy building the Walrus and Stranraer, and its parent company, Vickers, was busy building the Wellington. The initial solution was to subcontract the work out.^[85] The first production Spitfire rolled off the assembly line in mid-1938,^[1] and was flown on 15 May 1938, almost 24 months after the initial order.^[86]

The final cost of the first 310 aircraft, after delays and increased programme costs, came to £1,870,242 or £1,533 more per aircraft than originally estimated.^[4] Production aircraft cost about £9,500. The most expensive components were the hand-fabricated and finished fuselage at approximately £2,500, then the Rolls-Royce Merlin engine at £2,000, followed by the wings at £1,800 a pair, guns and undercarriage, both at £800 each, and the propeller at £350.^[87]

Castle Bromwich[link]

Spitfire Mk IIA, P7666, EB-Z, "Observer Corps", was built by Castle Bromwich, and delivered to 41 Squadron on 23 November 1940.^{[nb 8]}

In 1935, the Air Ministry approached Morris Motors Limited to ask how quickly their Cowley plant could be turned to aircraft production. This informal asking of major manufacturing facilities was turned into a formal plan to boost British aircraft production capacity in 1936, as the Shadow factory plan, under the leadership of Herbert Austin. Austin was briefed to build nine new factories, and further supplement the existing British car manufacturing industry, by either adding to its overall capacity or capability to reorganise to produce aircraft and their engines.

Under the plan, on 12 July 1938, the Air Ministry bought a site consisting of farm fields and a sewage works next to Castle Bromwich Aerodrome in Birmingham. This shadow factory would supplement Supermarine's original factories in Southampton in building the Spitfire. The Castle Bromwich Aircraft Factory ordered the most modern machine tools then available, which were being installed two months after work started on the site.^[4] Although Morris Motors under Lord Nuffield (an expert in mass motor-vehicle construction) at first managed and equipped the factory, it was funded by government money. When the project was first mooted it was estimated that the factory would be built for £2,000,000, however, by the beginning of 1939 this cost had doubled to over £4,000,000.^[88] The Spitfire's stressed-skin construction required precision engineering skills and techniques outside the experience of the local labour force, which took some time to train. However, even as the first Spitfires were being built in June 1940 the factory was still incomplete, and there were numerous problems with the factory management, which ignored tooling and drawings provided by Supermarine in favour of tools and drawings of its own designs,^[89] and with the workforce which, while not completely stopping production, continually threatened strikes or "slow downs" until their demands for higher than average pay rates were met.^[90]

By May 1940, Castle Bromwich had not yet built its first Spitfire, in spite of promises that the factory would be producing 60 per week starting in April.^[88] On 17 May Lord Beaverbrook, Minister of Aircraft Production, telephoned Lord Nuffield and manoeuvered him into handing over control of the Castle Bromwich plant to Beaverbook's Ministry.^[91] Beaverbrook immediately sent in experienced management staff and experienced workers from Supermarine and gave over control of the factory to Vickers-Armstrong. Although it would take some time to resolve the problems, in June 1940, 10 Mk IIs were built;^[92] 23 rolled out in July, 37 in August, and 56 in September.^[93] By the time production ended at Castle Bromwich in June 1945, a total of 12,129 Spitfires (921 Mk IIs,^[94] 4,489 Mk Vs, 5,665 Mk IXs,^[95] and 1,054 Mk XVIs^[94]) had been built. CBAF went on to become the largest and most successful plant of its type during the 1939-45 conflict. As the largest Spitfire factory in the UK, by producing a maximum of 320 aircraft per month, it built over half of the approximately 20,000 aircraft of this type.

Production dispersal[link]

This Spitfire PR Mk XI (PL965) was built at RAF Aldermaston in southern England

During the Battle of Britain, concerted efforts were made by the Luftwaffe to destroy the main manufacturing plants at Woolston and Itchen, near Southampton. The first raid, which missed the factories, came on 23 August 1940. Over the next month, other raids were mounted until, on 26 September 1940, both factories were completely wrecked,^[96] with 92 people being killed and a large number injured; most of the casualties were experienced aircraft production workers.^[97][98]

Fortunately for the future of the Spitfire, many of the production jigs and machine tools had already been relocated by 20 September, and steps were being taken to disperse production to small facilities throughout the Southampton area.^[96] To this end, the British government requisitioned the likes of Vincent's Garage in Station Square Reading, which later specialised in manufacturing Spitfire fuselages, and Anna Valley Motors, Salisbury, which was to become the sole producer of the wing leading-edge fuel tanks for photo-reconnaissance Spitfires, as well as producing other components. A purpose-built works, specialising in manufacturing fuselages and installing engines, was built at Star Road, Caversham in Reading.^[97] The drawing office in which all Spitfire designs were drafted was relocated to another purpose-built site at Hursley Park, near Southampton. This site also had an aircraft assembly hangar where many prototype and experimental Spitfires were assembled but having no associated aerodrome no Spitfires ever flew from Hursley.

Four towns and their satellite airfields were chosen to be the focal points for these workshops:^[96]

• Southampton and Eastleigh Airport
• Salisbury with High Post and Chattis Hill aerodromes^{[nb 9][99]}
• Trowbridge with Keevil aerodrome
• Reading with Henley and Aldermaston aerodromes.

Completed Spitfires were delivered to the airfields on large Commer "Queen Mary" low-loader articulated trucks, there to be fully assembled, tested, then passed on to the RAF.^[97]

Flight testing[link]

All production Spitfires were flight tested before delivery. During the Second World War, Jeffrey Quill was Vickers Supermarine's chief test pilot, in charge of flight-testing all aircraft types built by Vickers Supermarine; he also oversaw a group of 10 to 12 pilots responsible for testing all developmental and production Spitfires built by the company in the Southampton area.^{[nb 10]} Quill had also devised the standard testing procedures which, with variations for specific aircraft designs, operated from 1938.^[100][101] Alex Henshaw, chief test pilot at Castle Bromwich from 1940, was placed in charge of testing all Spitfires built at that factory, coordinating a team of 25 pilots; he also assessed all Spitfire developments. Between 1940 and 1946, Henshaw flew a total of 2,360 Spitfires and Seafires, more than 10% of total production.^[102][103]

Henshaw wrote about flight testing Spitfires:

After a thorough pre-flight check I would take off and, once at circuit height, I would trim the aircraft and try to get her to fly straight and level with hands off the stick ... Once the trim was satisfactory I would take the Spitfire up in a full-throttle climb at 2,850 rpm to the rated altitude of one or both supercharger blowers. Then I would make a careful check of the power output from the engine, calibrated for height and temperature ... If all appeared satisfactory I would then put her into a dive at full power and 3,000 rpm, and trim her to fly hands and feet off at 460 mph IAS (Indicated Air Speed). Personally, I never cleared a Spitfire unless I had carried out a few aerobatic tests to determine how good or bad she was. The production test was usually quite a brisk affair: the initial circuit lasted less than ten minutes and the main flight took between twenty and thirty minutes. Then the aircraft received a final once-over by our ground mechanics, any faults were rectified and the Spitfire was ready for collection. I loved the Spitfire in all of her many versions. But I have to admit that the later marks, although they were faster than the earlier ones, were also much heavier and so did not handle so well. You did not have such positive control over them. One test of manoeuvrability was to throw her into a flick-roll and see how many times she rolled. With the Mark II or the Mark V one got two-and-a-half flick-rolls but the Mark IX was heavier and you got only one-and-a-half. With the later and still heavier versions, one got even less. The essence of aircraft design is compromise, and an improvement at one end of the performance envelope is rarely achieved without a deterioration somewhere else.^[104][105]

When the last Spitfire rolled out in February 1948,^[106] a total of 20,351 examples of all variants had been built, including two-seat trainers, with some Spitfires remaining in service well into the 1950s.^[3] The Spitfire was the only British fighter aircraft to be in continuous production before, during and after the Second World War.^[11]

Operational history[link]

K9795, the 9th production Mk I, with 19 Squadron in 1938.

The operational history of the Spitfire with the RAF started with the first Mk Is K9789, which entered service with 19 Squadron at RAF Duxford on 4 August 1938.^{[4] [nb 11]} The Spitfire achieved legendary status during the Battle of Britain, a reputation aided by the famous "Spitfire Fund" organised and run by Lord Beaverbrook, the Minister of Aircraft Production.^[107] Although the key aim of Fighter Command was to stop the Luftwaffe's bombers, in practice the tactic was to use Spitfires to counter German escort fighters, particularly the Bf 109s, while the Hurricane squadrons attacked the bombers.^[108]

Well-known Spitfire pilots included J E "Johnnie" Johnson (34 enemy aircraft shot down),^[109] who flew the Spitfire right through his operational career from late 1940 to 1945. Douglas Bader (20 e/a) and R S "Bob" Tuck (27 e/a) flew Spitfires and Hurricanes during the major air battles of 1940, and both were shot down and became POWs while flying Spitfires over France in 1941 and 1942.^[110] Some notable Commonwealth pilots were George Beurling (31¹⁄₃ e/a) from Canada, A G "Sailor" Malan (27 e/a) from South Africa,^[111] New Zealanders Alan Deere (17 e/a) and C F Gray (27 e/a)^[112][113] and the Australian Hugo Armstrong (12 e/a).^[114]

The Spitfire continued to play increasingly diverse roles throughout the Second World War and beyond, often in air forces other than the RAF. The Spitfire, for example, became the first high-speed photo-reconnaissance aircraft to be operated by the RAF. Sometimes unarmed, they flew at high, medium and low altitudes, often ranging far into enemy territory to closely observe the Axis powers and provide an almost continual flow of valuable intelligence information throughout the war. In 1941 and 1942, PRU Spitfires provided the first photographs of the Freya and Würzburg radar systems and, in 1943, helped confirm that the Germans were building the V1 and V2 Vergeltungswaffe ("vengeance weapons") by photographing Peenemünde, on the Baltic Sea coast of Germany.^[115]

In the Mediterranean the Spitfire blunted the heavy attacks on Malta by the Regia Aeronautica and Luftwaffe and, from early 1943, helped pave the way for the Allied invasions of Sicily and Italy. On 7 March 1942, 15 Mk Vs carrying 90-gallon fuel tanks under their bellies took off from the HMS Eagle off the coast of Algeria on a 600-mile flight to Malta.^[116] Those Spitfires V were the first to see service outside Britain.^[117] Over the Northern Territory of Australia, RAAF Spitfires helped defend the port city of Darwin against air attack by the Japanese Naval Air Force.^[118] The Spitfire also served on the Eastern Front: approximately a thousand were supplied to the Soviet Air Force. Though some were used at the frontline in 1943, most of them saw service with the Protivo-Vozdushnaya Oborona (English: "Anti-air Defence Branch").

During WWII, Spitfires were used by the USAAF in the 4th Fighter Squadron until replaced by P-47 Thunderbolts in March 1943.

The Spitfire is listed in the appendix to the novel KG 200 as "known to have been regularly flown by" the German secret operations unit KG 200, which tested, evaluated and sometimes clandestinely operated captured enemy aircraft during World War II.^[119]

Speed and altitude records[link]

The Spitfire Mk XI flown by Sqn. Ldr. Martindale, seen here after its flight on 27 April 1944 during which it was damaged achieving a true airspeed of 606 mph (975 km/h).

Beginning in late 1943, high-speed diving trials were undertaken at Farnborough to investigate the handling characteristics of aircraft travelling at speeds near the sound barrier (i.e., the onset of compressibility effects). Because it had the highest limiting Mach number of any aircraft at that time, a Spitfire XI was chosen to take part in these trials. Due to the high altitudes necessary for these dives, a fully feathering Rotol propeller was fitted to prevent overspeeding. It was during these trials that EN409, flown by Squadron Leader J. R. Tobin, reached 606 mph (975 km/h, Mach 0.891) in a 45° dive. In April 1944, the same aircraft suffered engine failure in another dive while being flown by Squadron Leader Anthony F. Martindale, RAFVR, when the propeller and reduction gear broke off. Martindale successfully glided the Spitfire 20 mi (32 km) back to the airfield and landed safely.^[120] Martindale was awarded the Air Force Cross for his exploits.^[121]

A Spitfire was modified by the RAE for high speed testing of the stabilator (then known as the "flying tail") of the Miles M.52 supersonic research aircraft. RAE test pilot Eric Brown stated that he tested this successfully during October and November 1944, attaining Mach 0.86 in a dive.^[122]

On 5 February 1952, a Spitfire 19 of 81 Squadron based at Kai Tek in Hong Kong reached probably the highest altitude ever achieved by a Spitfire. The pilot, Flight Lieutenant Ted Powles,^[123] was on a routine flight to survey outside-air temperature and report on other meteorological conditions at various altitudes in preparation for a proposed new air service through the area. He climbed to 50,000 ft (15,240 m) indicated altitude, with a true altitude of 51,550 ft (15,712 m). The cabin pressure fell below a safe level and, in trying to reduce altitude, he entered an uncontrollable dive which shook the aircraft violently. He eventually regained control somewhere below 3,000 ft (900 m) and landed safely with no discernible damage to his aircraft. Evaluation of the recorded flight data suggested that, in the dive, he achieved a speed of 690 mph (1,110 km/h, Mach 0.96), which would have been the highest speed ever reached by a propeller-driven aircraft, but it has been speculated this figure resulted from inherent instrument errors.^[120]

The critical Mach number of the Spitfire's original elliptical wing was higher than the subsequently-used laminar-flow-section, straight-tapering-planform wing of the follow-on Supermarine Spiteful, Seafang and Attacker, illustrating that Reginald Mitchell's practical engineering approach to the problems of high-speed flight had paid off.^[125]

Variants[link]

As its designer, R. J. Mitchell will forever be known for his most famous creation. However, the development of the Spitfire did not cease with his premature death in 1937. Mitchell only lived long enough to see the prototype Spitfire fly. Subsequently a team led by his chief draughtsman, Joe Smith, developed more powerful and capable variants to keep the Spitfire current as a front-line aircraft. As one historian noted: "If Mitchell was born to design the Spitfire, Joe Smith was born to defend and develop it."^[126]