Supermarine Spitfire variants

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The British Supermarine Spitfire was one of the finest fighter aircraft of its time. Unlike its counterpart, the Hawker Hurricane, it appeared to have immense room for future improvement. This would lead to 24 marks of Spitfire being produced throughout the Second World War in continuing efforts to keep up with the Luftwaffe and Royal Air Force requirements.

In total, there were 24 marks of Spitfire and many sub-variants within each mark. This article presents a brief history of the Spitfire through all its variants. It should be noted that the numbering of the variants does not necessarily imply a chronological order; for example, the Mk. IX was a stopgap measure brought into production before the marks VII and VIII to address the urgent needs of the air force which could not wait for the more ambitious designs of the preceding marks. It is sometimes difficult to identify the variant of an individual Spitfire as many aircraft were built as one variant and later modified to be like another variant.

There is an apparent discrepancy in Spitfire numbering schemes in that sometimes Roman numerals are used and sometimes Arabic numerals are used. This is due to changes in RAF numbering schemes. Up until the end of 1942, the RAF would always use Roman numerals for mark numbers. 1943 to 1948 was a transition period during which new aircraft entering service were given Arabic mark numbers but older aircraft retained their Roman numerals. From 1948 onwards, Arabic numerals were used exclusively. This article adopts the convention of using Roman numerals for the marks I through XVI and Arabic numerals for the marks 17 through 24.

[edit] Wing types

Spitfire used five different wing types, designated "A" through "E," which overall had the same dimensions but different internal arrangements of armament and fuel tanks.

• A
  • Eight .303 inch (7.7 mm) Browning machine guns, 300 rounds/gun
• B
  • Two 20 mm Hispano HS.404 cannons with 60 rounds/gun
  • Four .303 inch Browning machine guns with 350 rounds/gun
• C — "universal wing" allowing armament consisting of either "A" type, "B" type, or four 20 mm Hispano cannon with 120 rounds each. Main landing gear was strengthened and moved 2 inches (5.08 cm) forward to reduce the tendency to "nose over" on landing. There was added provision for a 250 lb (113 kg) bomb under each wing. In practice, most aircraft carried:
  • Two 20 mm Hispano HS.404 cannons with 120 rounds/gun
  • Four .303 inch Browning machine guns with 350 rounds/gun
• D — long-range wing for reconnaissance versions with armament replaced by fuel tanks
• E — universal wing allowing two weapon fits
  • Two 20 mm Hispano cannon with 120 rounds/gun
  • 2x .50 inch (12.7 mm) Browning M2 machine guns, 250 rounds/gun
• or
  • Four 20 mm Hispano cannon with 120 rounds/gun

Beginning with the Mk 21, the Spitfire had a new wing design armed with four 20 mm Hispano cannons.

Some Spitfires starting with the Mk V had wingtips removed to improve low-altitude performance. These aircraft are sometimes incorrectly referred to as "LF" versions. The "LF" designation referred to the low-altitude version of the Rolls-Royce Merlin engine and while many "LF" Spitfires indeed had the "clipped" wings, a number did not.

[edit] Mk I

Spitfire Mk Ia

Realizing that the initial order for 310 Spitfires was but the first of what was likely to be a long production run, Vickers started construction of a huge new factory in Castle Bromwich to build Spitfires, (in addition to the existing line in Woolston, Southampton).

In 1938, their forward thinking paid off when the Air Ministry placed an order for an additional 1000 Spitfires from the new factory. It was followed in 1939 by an order for another 200 from the Woolston factory and, only a few months later, another 450. This brought the total to 2,160, making it one of the largest buys in history.

The Woolston line started delivering the Mk I Spitfire in late 1937 with front-line service commencing in August 1938. The Mk  I was powered by the 1,030 hp (768 kW) Merlin Mk  II engine driving a two-blade wooden fixed pitch propeller. Unfortunately for the Spitfire pilot, the engine was an early carburettor power plant. This engine had floats that allowed fuel to enter the cylinders. These floats, however, would be pushed into their closed positions in a zero gravity manoeuvre causing the fuel to cease its circulation, in turn causing the engine to shut off. When the pilot pulled the aircraft back into a position of positive gravity, he would be greeted by oil, spitting from vents, ending up all over the windshield of the fighter.

Bf 109s (encountered in 1940 during the Battle of Britain) would simply dive away, knowing the Spitfire pilot's reluctance to follow. Only 77 Spitfire Mk 1s had been completed before a three-bladed, two-position, metal propeller was substituted which greatly improved performance, along with a bullet proof windscreen, armor around the two gas tanks and the seat and engine bulkheads, along with bulged side panels on the canopy which improved the pilot's headroom and, as an additional benefit, his view behind. With these improvements, the aircraft became the Mk Ia.

Only a few squadrons were equipped with the Spitfire in September 1939, therefore, the Hurricane would be the only fighter to see action in mainland Europe. However, by the start of the Battle of Britain in July 1940, supplies had improved to the point that 19 squadrons were flying Spitfires, while another 27 were equipped with Hurricanes. By the end of the Battle in October 1940, 565 Hurricanes and 352 Spitfires had been lost.

At this point, the factories were at full production and the losses could easily be replaced (not so the pilots however). Production of the Hurricane as a front-line fighter was ramped down.

19 Squadron received several cannon-armed Spitfires known as the Mk  IB during the Battle. The cannon's hitting power was recognised but jamming was a serious problem. In one engagement, only two of the 12 aircraft had been able to fire off all of their shells. Further cannon-armed Spitfires were nevertheless issued to 92 Squadron and it was eventually realised that the best armament mix was an aircraft with two cannon and four machine guns.

In all, 1,566 of the original 2,160 Mk Is were delivered before production switched to the updated Mk  II.

[edit] PR Mk I Types — Early Reconnaissance Versions

Before the Second World War, the conventional wisdom was to use converted bomber types for airborne photo reconnaissance. These bombers retained their defensive armament, which was vital since they were unable to avoid interception.

In 1939, Flying Officer Maurice Longbottom was among the first to suggest that airborne reconnaissance may be a task better suited to fast, small aircraft which would use their speed and high service ceiling to avoid detection and interception. He proposed the use of Spitfires with the armaments and radios removed and replaced with extra fuel and cameras.

As a result, Spitfires were used for reconnaissance throughout the war. The original reconnaissance models were based on the Mk. I as follows:

• The PR Mk IA had two F .24 cameras with five inch focal length lenses which could photograph a rectangular area below the aircraft. They were installed in the wing space vacated by the inboard guns and their ammunition containers as a stop-gap measure. It had been envisaged that much larger cameras would be installed in the fuselage immediately behind the pilot, but at the time the engineering capacity required to make this conversion to the Mk  I was not available.
• In the PR Mk IB the camera lenses were upgraded to an 8 inch focal length, giving images up to a third larger in scale. It also had an extra fuel tank in the rear fuselage and was designated a medium range aircraft.
• The PR Mk  IC carried more fuel still and was the first photo reconnaissance aircraft to reach as far as Kiel. The extra fuel was carried in a tank behind the pilot and a blister tank under the port wing, which was counterbalanced by a camera installation on the starboard wing.
• The PR Mk ID was the backbone of RAF photographic reconnaissance in 1941 and 1942. It carried so much fuel that it was nicknamed "the bowser." Early production models were very badly balanced and consequently difficult to fly. Despite these difficulties the type quickly proved its worth, photographing such long distance targets as Stettin, Marseilles, Trondheim and Toulon. Later models were better balanced, had the more powerful Merlin 45 engine as used by the Mk V, and had heated cabins which were a great comfort to pilots on such long flights. A total of 229 Type Ds were built and the type was later re-designated the PR Mk IV.
• The PR Mk IE was built to address a requirement for oblique close-ups as opposed to high altitude vertical pictures. It is believed that only one Type E was built, N3117. It carried a single F .24 camera under each wing looking downwards at about 15 degrees below the horizontal. It proved most useful as it was able to photograph targets under weather conditions that would make high altitude photography impossible.
• The PR Mk IF was a "super-long-range" version which entered service in July 1940. It was a useful enough improvement that nearly all existing Type Bs and Type Cs were eventually converted to the Type F standard. Operating from East Anglia it was just able to reach, photograph, and return from Berlin.
• The PR Mk IG performed a similar role as the Type E before it. However the Type G carried the normal eight gun fighter armament as otherwise the aircraft would have been very vulnerable to enemy fighters. It was designed to photograph its targets from just below the cloud base, wherever that happened to be.

[edit] Mk II

Spitfire Mk IIa

With the end of the Battle of Britain, the RAF gained some breathing room over the winter of 1940/41. They took this opportunity to work several additions into the production lines, creating the Type 329 Spitfire Mk. II.

Chief among the changes was the upgraded 1,175 hp (876 kW) Merlin XII engine. The added power boosted top speed by 15 knots (28 km/h), and improved climb rate somewhat. The climb rate would have been improved further if not for the addition of 75 lb (34 kg) of armour plating around the pilot.

The Mk  II was produced both in the IIA eight-gun and IIB cannon armed versions. Deliveries were very rapid, and they quickly replaced all remaining Mk Is in service, which were then sent to training conversion units. The entire RAF had re-equipped with the new version by April 1941, and a total of 920 were built.

[edit] Mk  III and Mk IV

With the Mk II proving a match for the Luftwaffe fighters, the RAF asked Supermarine for much more ambitious upgrades to the basic design. Two proposals resulted.

The Mk. III was an airframe improvement, strengthening the design overall, adding additional covers and fillets over various openings, and the fitting of a retractable tail wheel. Combined with the improved Merlin XX engine, it was expected that the Mk  III would gain considerable airspeed and be able to fly at just over 400 knots (740 km/h).

The first Griffon-Spitfire, DP845

The Mk  IV was much more radical. Although it was based on a similar airframe to the Mk  III, it also included the new Rolls-Royce Griffon engine with over 1,500 hp (1,100 kW) available. This extra power not only boosted the speed to over 420 knots (780 km/h), but allowed for a much heavier six-cannon armament. The Mk  IV appeared so promising that Mk  III was abandoned in its favour. Plans were made to have the new design reaching squadron service in October, becoming the standard RAF fighter by the start of 1942, but it was not to be. It turned out that the Mk  XII would be the first Griffon powered Spitfire to enter service.

As the Rolls-Royce Griffon began to replace the famous Merlin and speeds went up, it was discovered just how advanced the design of the Spitfire's wings were: with a safe Mach number of 0.83 and a maximum Mach number of 0.86, the Spitfire's wing was able to reach higher speeds without Mach-induced flutter than many much newer designs.

[edit] Mk  V

Spitfire Mk Vb

The Mk V variant would be the most numerous of the type. Over six thousand were built.

Late in 1940, the Mk  II started meeting a new German aircraft in combat. Essentially a cleaned up version of the Messerschmitt Bf 109E that Spitfires and Hurricanes had bested the year before in the Battle of Britain, the new 109F or Friedrich model was superior to the Mk  II Spitfire in many respects. Not only was it able to outperform the Mk  II Spitfire in speed and rate of climb, it also was able to outturn it above about 18,000ft – something previously unheard of.

At this point, the Mk  IV was not going to be ready in time to counter the new Friedrich. Meanwhile the Griffon was running into very serious production problems and it wasn't clear if it would ever be ready. As an emergency stop-gap measure was needed as soon as possible: this was the Mk  V.

The Mk  V was nothing more than a Mk  II with the newer Merlin 45 series engine. This engine delivered slightly more takeoff power at 1,440 hp (1,074 kW), but greatly increased the power available at higher altitudes due to a new single-speed single-stage supercharger design. The new engine also allowed the Spitfire to move into zero gravity manoeuvres without any problems with fuel flow. This was a welcome new feature to the RAF pilots who had a new nasty surprise for their German enemies. Additionally, the aircraft could reach a top speed of 375 mph at 13,000 ft. It could climb to 20,000 ft in 7.5 minutes and its range was 470 miles on internal fuel alone and 1,135 miles on internal and external fuel. While it was no Mk  IV, the Mk  V was able to hold its own with the 109Fs it was meeting.

The Mk  V had metal ailerons where previous versions had fabric covered ailerons. This made it easier to manoeuvre the aircraft as less force was required to move the new ailerons. Because they were the same size and shape as the old ailerons they were retrofitted to a number of Mk  IIs. Douglas Bader had the Mk  IIs of his wing fitted with the new ailerons after contacting the factory directly without making an official request. Since his airfield was so close to the factory he simply arranged for the fighters to fly to the factory airfield and be refitted one at a time.

Timing played an important part, as over the winter a serious problem appeared in the tail structure of the Friedrich, and all production was halted. The problem wasn't solved until the early spring, by which time, the Mk  V had already started deliveries.

It would turn out that the problems with the Mk  IV's Griffon engine were as bad as some suspected, and it would be another two years before versions with that engine would enter service. The Mk V variant was the first Spitfire to see extensive overseas service, the first batch being shipped to Malta in March 1942. The variant (fitted with anti-sand air filters) would also equip units of the Desert Air Force during the North African campaign by August 1942. Here, the Mk Vcs were used as tactical fighter-bombers in addition to their interception role by being equipped with a maximum clearance load of 500 lbs of bombs. Mark Vb's equipped the 4th, 31st, and 52nd Fighter Groups of the USAAF in the summer of 1942, and the latter two groups continued flying them until succeeded by Spitfire IXs in mid-1943.

About 250 Mk Vc Spitfires were shipped to Australia to be used by No. 1 Wing Royal Australian Air Force, based in Darwin from early 1943 onwards. Mk Vcs had a new ability to carry different armament fits of either the eight 0.303" gun setup, the "B" type setup of 2 X 20 mm cannon with 4 X 0.303" guns or the new "C" type armament of 4 X 20 mm cannon. The new "C" type wing fitted to the Mk Vc (thus the "C" suffix after the variant name) also could accommodate 120 rounds per belt-fed cannon, unlike the "B" type wing which could only hold 60 rounds per cannon due to its barrel-fed cannon which would jam less due to the barrel feed system. These Mk Vcs were employed as interceptors against Japanese air raids. The Mk Vc versions received by the RAAF proved unreliable and — initially at least — had a relatively high loss rate. This was due to several factors, including pilot inexperience, engine overspeed due to the loss of oil from the propeller speed reduction unit (a problem resolved by the use of a heavier grade of oil),[1] and the practice of draining glycol coolant before shipment, resulting in internal corrosion. As mentioned above, any Spitfire Mk V sent overseas had a performance-reducing Vokes air filter to prevent the suction of excess moisture, sand and other foreign objects found more in tropical and hot desert climates.

In total, production was 94 of the eight gun Mk Va, 3,923 cannon armed Mk Vb and 2,447 of the Mk Vc.

[edit] Mk  VI

At the time that the Mk  V was placed in production there were growing fears that the Luftwaffe were about to start mass producing very high flying bombers such as the Junkers Ju 86, which could fly above the reach of most fighters of the time. It was decided that a new Spitfire variant would be required with improved high altitude performance.

The Mk  VI therefore contained two main refinements. For increased power at high altitudes, where the atmosphere is much thinner, it had a four-bladed propeller. To counter the physiological problems encountered by pilots at high altitudes, it had a pressurised cabin. It should be noted that the cabin is not like the fully pressurised cabin of a modern air liner; the pressure differential was only two pounds per square inch. The effect is to make 37,000 ft seem like 28,000 ft to the pilot, who would still have to wear an oxygen mask.

Despite these efforts, the Mk  VI did not handle well at high altitude and was unpopular with operational squadrons.

[edit] Mk  VII

Like the Mk  VI, the Mk  VII was a high altitude pressurised variant. However it had a number of refinements. It had a new engine, the two-stage Merlin 61, and the airframe was strengthened accordingly to carry the extra burden. It had a new, compact Aero-Vee air filter replacing the old, retro-fitted Vokes filter of the Mk V. It carried extra fuel in two small wings tanks. Most dramatically, Mk  VIIs began to be fitted with the "Lobelle" type hood which opened by sliding backwards, as on non-pressurised versions of the Spitfire. This was a big improvement on the clamp down cockpit of the Mk  VI.

There had been some instances of earlier models breaking up in the air in steep high speed dives. It was thought that this may have been due to aileron flutter. To address this, the Mk  VII had its ailerons reduced in span by 8.5 inches to reduce the length of aileron outboard from its hinges. It was later concluded that the break-ups were actually due to longitudinal-instability, resulting from incorrect loading of the aircraft on the squadrons causing the centre of gravity to be outside the safe limits.

In total, 140 Mk  VIIs were built, the last of which used the Merlin 71 engine and reportedly had superb high altitude performance with a service ceiling of 45,100 feet. For instance, French ace Pierre Clostermann recalls in his book, The Big Show, the successful interception of a reconnaissance Messerschmitt Bf 109 by a Mk VII from No. 602 Squadron RAF at 40,000 feet over the British Home Fleet's base at Scapa Flow in early 1944.

[edit] Mk  VIII

Spitfire Mk VIII

The Mk  VIII was an adaptation of the Mk  VII without the pressurised cabin, and was intended to become the main production model of the Spitfire.

Apart from the lack of pressurization, the Mk  VIII differed from the Mk  VII in few respects. Some early production models had extended wing spans but the majority did not. There were two sub-variants for low altitude (LF Mk VIII) and high altitude (HF Mk VIII) which were powered respectively by the Merlin 66 and Merlin 70 engines. The Spitfire Mk VIII also featured a retractable tail wheel unit and a wide-chord rudder, sometimes nicknamed the "Griffon rudder" due to the fact that this large control surface was often applied on Spitfires possessing Griffon engines, which caused more torque that could simply be countered by this larger tail surface. In comparison to the Mk V and like the Mk VII, each aileron of most MK VIIIs was shortened by 8.5" and the elevators were each slightly enlarged. In addition, general reinforcement of the fuselage was applied to the aircraft, making it slightly heavier than the Mk IX. Maneuverability, however, remained the same as the Mk IX except for roll rate, in which the Mk IXs maintained superiority due to its longer airlerons.

Performance was also increased with each modification. The F.Mk VIII's top speed was increased to 408 mph at 25,000 ft (404 mph for the LF.Mk VIII at 21,000 ft. and 416 mph for the HF.Mk VIII at 26,500 ft.) with a service ceiling of 43,000 ft (41,500 ft. for the LF.Mk VIII and 44,000 ft. for the HF.Mk VIII). Internally, the aircraft had — like the Mk VII — the addition of wing leading-edge fuel tanks (each containing 12.75 Imperial Gallons). The main tank changed with the addition of an extra 11 Imp. Gal. totalling at 96 Imperial Gallons, allowing the fighter to fly for a maximum distance of 660 miles with a full internal fuel load and 1,180 miles with a full internal load in addition to a 90-Imperial Gallon drop tank. With a 170-Imp. Gal. tank, the aeroplane could fly over 1,500 miles. The new control surfaces maintained good agility despite the additional torque and the amplification of split stream effect induced by the more powerful engine. The Mk VIII — though agile — did not maintain a turning radius as tight as the earlier Mk V.

Armament consisted of the regular "C" wing type standard. This armament type could include either four Hispano 20 mm cannon with 120 rounds per gun (rpg) or two 20 mm cannon with 120 rpg along with 4 X Browning 0.303" machine guns with 350 rpg or 8 X 0.303" guns with 350 rpg. An external bomb load could accommodate 1,000 pounds (1 x 500 lb bomb attached the centre bombrack. 2 x 250 lb bombs, one under each wing). The thin wings, however, would not be fitted with bombs when armed with the quadruple cannon armament, nor could they accommodate an armament of four cannon with four machine guns.

A Mk  VIII was used to experiment with the use of a new cut-back rear fuselage and a "tear-drop" canopy. This was intended to aid pilot visibility; many Spitfire pilots who were shot down were done in by enemies who approached in the aircraft's blind spot. In trials, the new hood design was found to be an enormous improvement to all-round visibility, although there were some problems reported opening and closing the hood when the aircraft was travelling at speed and the hood was thought to be too claustrophobic.

This variant served almost exclusively overseas in the Mediterranean with both the Desert Air Force and the USAAF, and in the Pacific beginning in 1943 with the Royal Australian Air Force.

In the Mediterranean Theatre in Italy, the Mk VIII fought with the United States Army Air Force. The 31st and 52nd Fighter Groups operated the fighter for some time until, in March 1944, they had their aircraft replaced by — according to many 31st FG members — the "inferior" P-51 Mustang, needed for the growing necessity of long-range escort fighters. Over 300 kills were claimed by the two fighter groups while flying Spitfires.

In the Pacific, its standard range was considered insufficient as unlike carrier-based aircraft, the aircraft could not operate at long distances over sea and could not land on carriers if in danger. These disabilities, coupled with the challenging environment of the Pacific theatre also meant the Spitfire Mk VIII had a higher loss rate in battle than other Allied fighters operating in the Pacific, which, for the most part, were tougher Navy planes.

Nevertheless, the aircraft was a superb dogfighter and could outfly and outgun nearly every Japanese fighter it encountered. It was up to 50 mph faster than contemporary Japanese fighters and it was much more manœuvrable than its American counterparts. It could even be seen as an integration between the American need for speed and the Japanese yearning for manœuvrability. The fighter served mainly in the defence of Australia and found success against the more manœuvrable Japanese fighters by using an altitude and climb advantage. This additional height allowed the Spitfire to dive to gain speed, attack the enemy and climb out of range very quickly to avoid damage. After the Mk IX and Mk V, the Mk VIII was the third most numerous operational variant with 1,658 examples.

[edit] Mk  IX

Spitfire Mk IX with clipped wingtips

Spitfire Mk IX

Spitfire Tr Mk IX TE308 (twin seat).

Spitfire T Mk IX at RIAT 2004.

In the early months of 1942, there was much pressure to get Spitfires into production using the new two-stage supercharged Merlin 61 engine. Although the Mk  VII and Mk  VIII variants were to use the new engine, they were not yet ready for production. To solve this problem, a compromise was reached where the Mk  V was simply fitted with a Merlin 61 engine and the Mk  IX was born. The aircraft could now reach a top speed of about 410 mph at 25,000 ft and could fly to a maximum service ceiling of 42,000 ft. Although the Mk  IX's airframe did not have the aerodynamic improvements, strength improvements or the modified control surfaces of the Mk  VII and VIII that were really needed for the more powerful engine, the Mk  IX still proved to have vastly improved performance over the Mk  V and effectively countered the Focke Wulf Fw 190 in Western Europe.

Some 40 older Junkers Ju 86 bombers were converted to Ju 86P-1 high altitude bombers and Ju 86P-2 photo reconnaissance aircraft. These variants operated successfully for some years over Great Britain, the Soviet Union and North Africa, although, in August 1942, a modified Spitfire V shot one down over Egypt, and when two more were lost, Ju 86Ps were withdrawn from service in 1943.

Towards the end of September 1942, the Luftwaffe began launching high level bombing raids against England. Junkers Ju 86 R bombers flying at 40,000 feet were able to bomb England without impediment; the Spitfire Mk. VIs that tried to intercept them were unable to reach them. To counter the threat, a pair of Spitfire IXs were stripped of everything not required for the role of high level interception, lightening them by 450 pounds each. On 12 September 1942 one of the aircraft successfully intercepted a Ju 86R above Southampton at 41,000 ft. The ensuing battle went up to 43,000 ft and was the highest air battle of the war. However, the Spitfire did not perform well enough at that altitude to be decisive; whenever the pilot had a shot lined up, the aircraft would slew and fall out of the sky. The bomber escaped safely with just one hit to its port wing, but having proven to be vulnerable to the RAF at high altitudes, the Luftwaffe launched no further high altitude attacks against England.

In the summer of 1944, several major improvements were made to Mk  IXs coming off the production line:

• They were fitted with the Mark II Gyro Gunsight. This gunsight calculated the correct angle of deflection to use when leading the target. Its introduction doubled the effectiveness of their gunnery and was a major factor in Allied air superiority.
• The "E Type" wing was introduced. It removed the .303 machine guns mounted in the outer wings as most aircraft at that time had armour impenetrable by .303 bullets. The 20 mm Hispano cannon were moved outboard and the more effective .50 calibre Browning heavy machine gun was introduced. The improved armament was more effective for both air-to-air engagements and air-to-ground attacks. Ailerons, however, remained the same length as those of the Mk V, unlike those of many Mk VIIs and VIIIs which were shortened.
• As a result of its over-powerful engine and four-bladed propeller, the Mk  IX had a tendency to swing to one side during takeoff. This was solved by fitting a larger rudder, giving the pilot better control during takeoff. As well, the landing gear was strengthened and moved two inches toward the nose to reduce the chances of nosing over. One radiator and oil cooler was placed under each wing creating a more symmetrical appearance.
• The cut-back rear fuselage and bubble canopy, prototyped on a Spitfire Mk  VIII, was incorporated into the model. However, the Mk IX often utilized a fully bulged "Malcolm hood," named after its inventor, unlike the earlier Malcolm canopy on the Mk I-V which used hoods only bulged at the top.
• Extra internal fuel tanks were fitted, as the Spitfire had an embarrassingly short range of merely 434 miles when operating on its full internal fuel load of 85 Imperial Gallons. External wing tanks had been used as a temporary measure, but they increased drag and had to be jettisoned before entering combat. Only the very latest of Mk IXs were fitted with the additional internal fuel tanks in the rear fuselage. This configuration gave them a range of over 1,200 miles with full internal and external fuel loads at the expense of manœuvrability, however, enemy aircraft were not very common by this time.

The Spitfire T Mk IX was a two-seat training version of the standard Mk IX. The T Mk IX was exported to India and Ireland.

The Mk. IX was the one of the most numerous variant of Spitfire produced. In total, 5665 entered service.

[edit] Mk  X and Mk  XI

The Mk  XI was a reconnaissance aircraft based on a combination of features from the marks VII, VIII and IX. The cameras, two vertically-mounted and sometimes an obliquely-mounted one, were installed in the fuselage behind the cockpit. The first Mk  XIs were built in November 1942 and lasted until 1944 when they were phased out in favour of the Mk  19.

The Spitfire Mk  X followed the Mk  XI into production and was nearly identical. It had a pressurised cabin and a Lobelle sliding hood, and gave similar performance. Only 16 Mk  Xs were made, and these saw limited service for high altitude reconnaissance.

[edit] Mk  XII

Spitfire F Mk XIIs of 41 Sqn

The Mk  XII was the first Spitfire powered by a Griffon engine to go into service. The first production models started appearing in October 1942 and in total, two RAF squadrons were equipped with the model. Mk XIIs were converted from Mk V, Mk VIII or Mk IX airframes and most of these machines had a single 85 Imp. Gal. main fuel tank, giving a short range of little over 380 miles on internal fuel. The latest Mk XIIs, however, had two wing fuel tanks, each containing a maximum fuel load of 28 Imp. Gal. Despite this defficiency, the Griffon engine gave the aircraft superb low and medium level performance. In fact at low altitude it was one of the fastest aircraft in the world; in one speed trial a prototype Mk. XII (DP845) raced ahead of a Hawker Typhoon and a captured Focke-Wulf Fw 190 to the amazement of the dignitaries present. However pilots found it difficult to exploit this advantage in combat as German pilots were reluctant to be drawn into dog fights with Spitfires of any type below 20,000 feet. The Mk  XII's speed advantage was only really useful near the end of its front line service in Summer 1944, in which it shot down a respectable number of V-1 Flying Bombs. The Mk  XII variant was retired in September 1944.

[edit] PR Mk  XIII

The PR Mk  XIII was an improvement on the earlier PR Type G with the same camera system but a new engine, the Merlin 32, which was specially rated for low-altitude flight. It carried a light armament of four .303 Browning machine guns. The first prototype Mk  XIII was tested in March 1943.

Twenty six Mk  XIIIs were converted from either PR Type G, Mk  II or Mk  Vs. They were used for low level reconnaissance in preparation for the Normandy landings.

[edit] Mk  XIV

Spitfire Mk XIV

The first Griffon powered Spitfires suffered poor high altitude performance due to having only a single stage supercharged engine. By 1943 Rolls-Royce engineers had put together a new Griffon engine — the 61 series — with a two-stage supercharger. In the end it was a slightly modified engine, the 65 series, which was used in the Mk  XIV. The resulting aircraft was as great an improvement over the Mk  IX as the Mk  IX had been over the Mk  V. Although initially based on the Mk  VIII airframe, common improvements made in aircraft produced later included the cut-back fuselage and tear-drop canopies, and the E-Type wing with improved armament.

As the next major step in the Spitfire's evolution, the Mk XIV's Griffon engine produced 2,050 HP at altitude. It could climb to 20,000 ft. in less than seven minutes and its top speed — which was achieved at 26,000 ft. — was 448 mph. F Mk XIVs had an 85 Imperial Gallon main tank and a 12.75 Imp. Gal. fuel tank in each leading edge wing tank. Unfortunately, the fighter's maximum range was just a little over 450 miles on internal fuel since the new Griffon engine consumed much more fuel per hour than the original Merlin engine of earlier variants. By late 1944, Spitfire XIVs were fitted with 75 Imp. Gal. in a rear fuselage fuel tank. Mk. XIVs with "tear-drop" canopies had 64 Imp. Gal. and the FR Mk XIV (the armed reconnaissance version), with its tear drop-shaped canopy and port fuselage camera, had an additional rear fuel tank with 33 Imp. Gal. As a result, F Mk XIVs had a range that was increased effectively to over 600 miles on internal fuel while the FR Mk  XIV had a marginal increase in range. A 90 Imp. Gal. drop tank was often fitted to these Griffon Spitfires to give even more range.

The first test of the aircraft was in intercepting V1 flying bombs, with the Mk  XIV was the most successful of all Spitfire marks in this role. The new Griffon engine — to the surprise of a few test pilots — rotated anti-clockwise when seen from behind, unlike the Merlin engines which spun their propellers in the opposite direction. This caused a mirrored split stream effect which could sway the aircraft strongly to the right. Fortunately, pilots became used to this feature and later, the Mk  XIV was used by the 2nd Tactical Air Force as their main high-altitude air superiority fighter in northern Europe. In total 957 Mk  XIVs were built, over 400 of which were FR Mk XIVs. After the war, second hand Mk  XIVs were exported to a number of foreign air forces; 132 went to the Royal Belgian Air Force, 70 went to the Royal Indian Air Force and 30 of its reconnaissance variant went to the Royal Thai Air Force.

[edit] Mk  XV and Mk  17

The XV and 17 marks were reserved for the naval version, the Seafire, in an effort to reconcile the Spitfire numbering scheme with that of the Seafire.

[edit] Mk  XVI

Spitfire Mk XVI

The Mk  XVI was identical to the Mk  IX in nearly all respects except for the engine, a Merlin 266. The Merlin 266 was a low-altitude version of the Merlin 66 and was built under licence in the USA by the Packard Motor Company. All Mk XVI aircraft produced were of the Low-Altitude Fighter (LF) variety. This was not determined by the length of the wings (clipped wings were fitted to most LF Spitifres), but by the engine, which had been built for low-altitude work. All production Mk XVIs had clipped wings for low altitude work.

Armament for most Mk XVIs consisted of two 20mm (0.79") cannon, each with 120 rounds and two 0.5" (12.7mm) calibre machine guns, each with 500 rounds, though these two guns could be replaced with 20mm cannon. A single 500 lb. (227 kg) bomb could be carried underneath the centre rack, and one 250 lb. (114 kg) bomb could be slung under each wing. The centre rack could also hold a slipper-type drop tank, which had been used by many preceding Spitfires. Some production aircraft had wing fuel tanks in addition to the main tank which allowed it to fly approximately as far as the Spitfire Mk VIII. Problems with the licence-built engines limited introduction to front-line squadrons for several months.

[edit] Mk  18

Spitfire Mk 18

The Mk  18 was a refinement of the Mk  XIV. It was identical in most respects including engine (the Griffon 65) and cockpit enhancements, but it carried extra fuel and had a revised, stronger wing structure. Its handling was also nearly identical and so it was not put through any performance tests. Like the Mk  XIV before it, there were fighter and fighter reconnaissance variants built.

The Mk  18 missed the war. It was built up until early 1946 but it was not until January 1947, that an RAF squadron, No. 60 Squadron RAF which operated from RAF Seletar, Singapore, was re-equipped with the variant. Later, other squadrons in the Far East and Middle East would receive them. Some 300 Mk  18s were built but they saw little action apart from some involvement against guerrillas in the Malayan Emergency. The Royal Indian Air Force purchased 20 ex-RAF Mk  18s in 1947.

[edit] Mk  19

Spitfire PR Mk 19. This particular plane (PS890) was modified in 2002 to use a Griffon engine from an Avro Shackleton driving a contra-rotating propeller. Originally, a normal five-blade propeller was fitted. Note the small view hole for the camera between the cockpit and the insignia

The Mk  19 was the last and greatest photographic reconnaissance variant of the Spitfire. It combined features of the Mk  XI with the Griffon engine of the Mk  XIV. After the first 25 were produced, later aircraft were also fitted with the pressurised cabin of the Mk  X and the fuel capacity was increased to 256 gallons, three-and-a-half times that of the original Spitfire.

The first Mk  19s entered service in May 1944, and, by the end of the war, the type had virtually replaced the earlier Mk  XI. A total of 225 were built with production ceasing in early 1946, but they were used in front-line RAF service until April 1954. In fact, the last time a Mk  19 was used to perform an operational sortie was in 1963 when one was used in battle trials against an English Electric Lightning to determine how best a Lightning should engage piston engined aircraft. This information was needed in case RAF Lightnings might have to engage P-51 Mustangs in the Indonesian conflict of the time.

[edit] Mk  XX

Only two aircraft were ever designated Mk  XX and they were both prototypes for other marks. The first was DP845. Initially a Mk  IV, it was re-designated a Mk  XX shortly after its maiden flight on 27 November 1941 and was later refitted to be the prototype Mk  XII. The Mk  IV designation was taken over by the PR Type D.

The second Mk  20, DP851, initially had a Griffon II engine and made its first flight in August 1942. In December, it was refitted with a Griffon 61 and re-designated as a Mk  21 initial prototype.

[edit] Mk  21

In early 1942, it was evident that Spitfires powered by the new two-stage supercharged Griffon 61 engine would need a much stronger airframe, in particular with stiffer wings. The proposed new design was designated the Mk  21. However its initial design had a number of flaws that caused considerable damage to the otherwise excellent Spitfire reputation.

Aside from the more powerful engine, the Mk  21 had several notable features:

• The propeller was changed to a five-bladed propeller with a diameter 7 inches greater than that fitted to the Mk  XIV.
• To ensure sufficient ground clearance for the new propeller, the undercarriage legs were lengthened by 4.5". To improve handling on the ground, the undercarriage legs were placed 7.25" further apart than before. These modifications presented a problem to the designers because the larger undercarriage did not have enough space in which to retract. They solved this problem with a system of levers that compressed the undercarriage legs by about eight inches as they retracted, and extended the legs again when they were lowered.
• The armament was standardised to four cannon and no machine guns.

In other respects, the first production Mk  21s used the same basic airframe as the Mk  XIV. However the modifications over the Mk  XIV left the aircraft over sensitive to trimming and it exhibited poor performance in trials in late 1944 and early 1945. This led to a damning report from the Air Fighter Development Unit in which they recommended that, "No further attempts should be made to perpetuate the Spitfire family."

This report caused serious concern for Supermarine as their factory at Castle Bromwich had already been converted to produce Mk  21s and more were coming off the production lines every day. Luckily, the most serious problems were easily solved by changing the gearing to the trim tabs and other subtle control modifications, with the result that the aircraft was cleared for instrument flying and low level flying in trials in March 1945.

It was January 1945 before Spitfire 21s became operational. They had little opportunity to engage the enemy before the war ended, but scored a rare success on 26 April 1945, when two Spitfire Mk  21s shot up and claimed sunk a German midget submarine which they caught on the surface. With the end of the war most orders for the Mk  21 were cancelled. Only 120 were completed.

[edit] Mk  22

The Mk  22 was identical to the Mk  21 in all respects except for the fitting of a cut-back rear fuselage and tear-drop canopy. In previous marks these changes had not warranted a new mark designation. A total of 272 Mk  22s were built.

The Mk  22 was used by only one regular RAF unit, No. 73 Squadron RAF in the Middle East. However twelve squadrons of the Royal Auxiliary Air Force used the variant and continued to do so until March 1951.

[edit] Mk  23

The Mk  23 was to be a Mk  22 incorporating a revised wing design originally created for the Supermarine Spiteful. However when trialled on a Mk  VIII the new wing gave less than perfect handling characteristics and so the Mk  23 was never built.

[edit] Mk  24

The final Spitfire variant, the Mk  24 was similar to the Mk  22. It carried extra fuel and had wing fittings for rocket projectiles. Some were built with shorter-barrelled Mark V Hispano cannon.

A total of 81 Mk  24s were completed, 27 of which were conversions from Mk  22s. The last Mk  24 to be built was delivered in February 1948. They were used by only one RAF squadron, No. 80 Squadron RAF, until 1952. Some of the squadron's aircraft went to the Hong Kong Auxiliary Air Force where they were operated until 1955.

[edit] Comparison of Spitfire variants