The British Supermarine Spitfire was facing several challenges by mid-1942. The debut of the formidable Focke-Wulf Fw 190 in late 1941 had caused real problems for RAF fighter squadrons flying the latest Spitfire Mk Vb. Fortunately Rolls-Royce engineers were already working on a new version of the Merlin which would take the Spitfire to new levels of performance. The Rolls-Royce Griffon engine was promising even greater performance increases. The Supermarine design team under Joseph Smith would succeed in keeping the Spitfire updated and improved through to the end of the Second World War and beyond.
This article presents a brief history of the Spitfire through its Two-Stage Rolls-Royce Merlin and also in its Griffon engine variants. Experimental Spitfires and drawing board projects derived from the basic design are also described.
Many 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.IX. This designation referred to the low-altitude version of the Rolls-Royce Merlin engine and while many "L.F" Spitfires had the "clipped" wings, a number did not.
Beginning with the Mk. 21, the Spitfire had a new wing design armed with four 20 mm Hispano Mk II or V cannon.
With the development of the Merlin 61/63/66 and 70 series engines, with a two-stage, two-speed supercharger requiring an intercooler, several important modifications were made to the basic airframe and applied to all aircraft powered by these engines:
All Mk VII and Mk VIII Spitfires had the following changes:
Extended, "pointed" wingtips were fitted to the Type C wings, increasing the wingspan to 40 ft 2 in (12.2 m). Because the threat from high altitude bombers never materialised many Mk VIIs later reverted to the normal, rounded wingtip.
Mk VIIs began to be fitted with a "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. The canopy was double-glazed and used rubber tubing to create a proper pressure seal against the fuselage. The canopy rails were bulkier than the standard Spitfire type.
In total, 140 Mk VIIs were built by Supermarine, the last of which used the Merlin 71 engine and reportedly had superb high altitude performance, with a service ceiling of . 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 of 602 Squadron at over the British Home Fleet's base at Scapa Flow in early 1944.
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. When the "interim" Mk IX proved itself to be adequate for the RAF's needs it was decided to utilise the shadow factory at Castle Bromwich to produce that version only: the Mk VIII Spitfires were all built by Supermarine.
Apart from the lack of pressurisation, the Mk VIII differed little from the Mk VII. Some early production models had extended wingtips but the majority were fitted with the standard version. There were three sub-variants for low altitude (LF Mk VIII), medium altitude (F Mk VIII) and high altitude (HF Mk VIII) which were powered respectively by the Merlin 66, Merlin 63 and Merlin 70 engines.
According to Supermarine's Chief Test Pilot Jeffrey Quill:
A small number of Mk VIIIs were produced with four 20 mm cannon. A maximum external bomb load of 1,000 pounds (1 x bomb attached to the centre bombrack or 2 x bombs, one under each wing) could be carried. 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 JF299 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 so by enemies who approached in the aircraft's blind spot. In trials, the new hood design was found to bring about great improvements to all-round visibility and, with several modifications, was standardised on later Spitfires.
This variant served almost exclusively overseas in the Mediterranean, with both the Desert Air Force and the USAAF, and in the Pacific, with the Royal Australian Air Force and in the China-Burma-India theatre.
After the Mk IX and Mk V, the Mk VIII was the third most numerous operational variant with 1,658 examples.
In the early months of 1942, with the clear superiority of the Focke Wulf Fw 190 over the Spitfire VB. there was much pressure to get Spitfires into production using the new two-stage supercharged Merlin 61 engine. In September 1941 the Spitfire Mk III prototype N3297 had been converted by Rolls-Royce at their Hucknall plant to take a Merlin 60, which had been specifically designed for use in the Wellington Mk VI high altitude bomber. The performance increase was described as a "quantum leap" over that of the Mk VB and another Spitfire airframe, R6700 was modified to take the new engine. Although design work on the Mk VII and VIII series was under way, these would take over a year to get into production and a counter to the Fw 190 was urgently needed. As a result the Air Ministry made the decision that Mk VC airframes should be converted to take the more powerful engine.
As a result many of the early IXs were converted Mk VCs which did not have any of the refinements which later appeared. These could be identified by the Type C wing with the large double blisters over the inner cannon bays and the identification light on the fuselage spine, behind the aerial mast. The elevator horns were also smaller in size than that of most Mk IXs which had larger horn balances.
Although the Mk IX's airframe did not have the aerodynamic and strength improvements, or the modified control surfaces of the Mk VII and VIII, the Mk IX still proved to to be an effective counter to the Focke Wulf Fw 190; production of the Mk IX ended in April 1945 and, in combination with the Mk XVI this "compromise" was produced in larger numbers than any other Spitfire variant.
In September 1942 the "High Altitude Flight" was set up at RAF Northolt to counter the threat of the high altitude Junkers Ju 86 R bombers. Two Spitfire XIs converted from VCs were stripped of armour, the .303 Brownings and other equipment and repainted in a lightweight PRU blue finish. One of them successfully intercepted a Ju 86R at over .
Production of the Mk IX finished at Supermarine in June 1943, with production continuing exclusively at the Castle Bromwich factory. Several major improvements were made to Mk IXs coming off the production line:
F.R IXs were standard, armed Mk IXs modified with a single, port facing, oblique camera. These aircraft were used for low altitude "Dicing" missions in tactical support of army operations. 16 Squadron, which was a unit of the 2nd TAF, used several FR Mk IXs (painted a pale, "Camoutint" Pink, which provided excellent camouflage under cloud cover) to photograph the Arnhem area before Operation Market Garden.
Although there were wartime conversions of the Spitfire into a two-seat trainer including the one-off modification of a Mk VC by RAF no. 261 Squadron and a Mk IX converted for use as a trainer by the Soviets, the two-seat Spitfire trainer was primarily a postwar program. In 1946, a MK VIII (MT818) was the first Vickers-built trainer built as a demonstrator, but in 1948, 10 Spitfire T Mk IXs, were exported to India. In 1951, a further six TR 9 trainers were converted from the standard Mk IX to train pilots for the Irish Air Corps (IAC) Seafire fleet. The Spitfires provided transition training that included gunnery practice since the type was equipped with two .303 Browning machine guns, one in each outer wing bay. Most of the TR 9 aircraft passed to the ground technical training school at Baldonnel where they were used as instructional airframes for the training of aircraft engineers for the Air Corps. Four of the IAC aircraft survived and two went on to join the warbird fleet in the 1970s and later.
The Mk IX was the second most numerous variant of Spitfires produced. In total, 5656 were built, 561 by Supermarine and 5,095 by Castle Bromwich.
Physically the Mk XIs had a deeper nose fairing to accommodate a larger 14 gallon oil tank and it had the standard, unarmoured wrap-around PRU windscreen. "Booster" pumps for the wing tanks were fitted and covered by "teardrop" shaped fairings under the wings. In total 471 Mk XI were built by Supermarine. From April 1944 production ran concurrently with the P R Mk XIX before ending in December.
The Spitfire Mk X followed the Mk XI into production and was based on the reinforced Mk VII airframe with P.R Mk XI wings. It had a pressurised cabin and a Lobelle sliding hood, and gave similar performance. Only 16 Mk Xs were made, entering service in April 1944. All saw limited service in a high altitude reconnaissance role.
The Mk XVI was the same as the Mk IX in nearly all respects except for the engine, a Merlin 266. The Merlin 266 was the Merlin 66 and was built under licence in the USA by the Packard Motor Company. The "2" was added as a suffix in order to avoid confusion with the engines, as they required different tooling. 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 optimised for low-altitude operation. All production Mk XVIs had clipped wings for low altitude work. Many XVIs featured cut-down rear fuselages and were fitted with "bubble" canopies.
Because of a slightly taller intercooler and rearranged accessories on the Packard Merlins a new, bulged upper cowling was introduced and also appeared on late production IXs.
Armament for most Mk XVIs consisted of two 20 mm Hispano II cannon, each with 120 rounds and two .50 calibre Browning machine guns, each with 250 rounds. 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. Some production aircraft had rear fuselage 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. A total of 1,054 Mk XVIs were built by Castle Bromwich.
With the German invasion of Norway in April 1940 the RAF took an interest in the concept of using floatplane fighters in areas where airfields were not immediately available. To this end a Spitfire Mk I R6722 was taken in hand at the Woolston factory to be modified and mounted on Blackburn Roc floats. Tank tests were carried out at Farnborough, using a 1/7th scale model, it was found that the concept was basically sound, although the vertical tail surfaces would need to be enlarged to counter-balance the side area of the floats. The end of the Battle of Norway and the need for as many Spitfires as possible meant that R6772 was converted back to an ordinary fighter.
With the entry of Japan into the war the concept was revived in early 1942. A Spitfire V W3760 was fitted with a pair of floats 25 ft 7 in (7.8 m) long, mounted on cantilever legs. This aircraft was powered by a Merlin 45 driving a four bladed propeller of 11ft 3 in diameter (3.4 m). A Vokes filter was fitted to the carburettor air intake and under the tail an extra fin extension was added. Other changes included external lifting points forward of and behind the cockpit and a spin-recovery parachute with a rudder balance-horn guard. The Spitfire floatplane was first flown on 12 October 1942 by Jeffrey Quill. Soon afterwards the Vokes filter was replaced by an Aero-Vee filter, similar to that on later Merlin 61 series aircraft, which was extended to prevent water entry, and full Mk VB armament was installed. Two more VBs EP751 and EP754 were converted by Folland and all three floatplanes were transported to Egypt, arriving in October 1943. At the time it was thought that the floatplanes could operate from concealed bases in the Dodecanese Islands, disrupting supply lines to German outposts in the area which relied on resupply by transport aircraft. This scheme came to naught when a large number of German troops, backed by the Luftwaffe, took over the British held islands of Kos and Leros. No other role could be found for the floatplane Spitfires, which languished in Egypt, operating from the Great Bitter Lake. Specifications for the VB based floatplane included a maximum speed of 324 mph at 19,500 ft (521 km/h at 5,943 m), a maximum rate of climb of 2,450 ft/min at 15,500 ft (12.45 m/sec at 4,724 m) and an estimated service ceiling of 33,400 ft (10,180 m).
In the spring of 1944, with the prospect of use in the Pacific Theatre, a Spitfire IX MJ892 was converted to a floatplane. This used the same components as the earlier Mk VB conversions. Jeffrey Quill wrote:
Five aircraft were converted:
On 4 December 1939, the Supermarine design staff produced a brochure which mooted the idea of converting the Spitfire to use the Rolls-Royce Griffon engine. A top speed of 423 mph (681 km/h) at 18,500 ft (5,639 m) was predicted. However, constant problems with the development of the Griffon meant that the decision to proceed with building a Spitfire with this engine didn't come to fruition until 1942, with the successful flight trials of the Mk IV.
The Griffon IIB which powered the Mk IV was a single-stage supercharged engine of 1,735hp (1,293 kW). Stronger main longerons were needed to cope with the weight of the Griffon and it required a bigger radiator and oil cooler, although it kept the asymmetric under-wing radiator layout of the single stage Merlin marks. The new engine had a lower thrust-line than the Merlin and was set with a minus ½ degree of downthrust. The lower thrust line and larger capacity of the new engine meant that the contours of the engine cowling were completely changed, with more prominent blisters over the cylinder heads, plus a third tear-drop shaped blister on the upper forward cowling to clear the magneto, and a deeper curve down to the spinner, which was much longer than previous types. The lower cowling lost its "pigeon-chested" appearance, with a shallower curve up to the spinner. A four blade Rotol propeller of 10 ft 5 in (3.1 m) was used. Apart from these differences the Mk IV airframe was closely related to that of the Merlin powered Mk III. One feature of the Griffon engine which was to catch a lot of pilots out was that the propeller rotated in the opposite direction to that of the Merlin; ie: to the right, from the pilot's perspective, rather than to the left. This meant that the powerful slipstream swung the Spitfire to the right on the ground, requiring the rudder to be deflected to the left during takeoff.
The Mark IV DP845 first flew on 27 November 1941. It had the full span C wing combined with a small tail unit and retractable tailwheel, and also had external bracket hinges under the wings, denoting the installation of braking flaps. These were soon removed and a mock up of a proposed six-cannon armament was fitted, three in each wing. The aircraft was soon renamed Mk XX, to avoid confusion with a renamed PR type, then it became the Mk XII.
Jeffrey Quill was Vickers Supermarine's chief test pilot and was instrumental in test flying and assessing every development of the Spitfire from the prototype K5045 to the last production Mk 24s, as well as some marks of Seafire. His assessment of the Mk IV/Mk XII prototype DP845 was;
The Mk XII was the first Spitfire powered by a Griffon engine to go into service. The first of 100 Supermarine built production models started appearing in October 1942, and in total, two RAF squadrons were equipped with the model. Mk XIIs were manufactured from Mk VC and Mk VIII airframes: early production aircraft had the fixed tail wheels, five spoke mainwheels and small elevator balances. They had a single 85 gallon main fuel tank, giving a short range of little over on internal fuel. All were fitted with the larger, pointed tip rudder. The last 45 or so Mk XIIs, were based on Mk VIIIs with two wing fuel tanks, each containing a maximum fuel load of 14 gallons, and featured the larger horn balances, retractable tailwheel and undercarriage legs with torque-links, "dished" leg fairings and the reinforced four spoke wheels. The wheels were occasionaly fitted with disc-style covers. A later model IFF was fitted, replacing the aerials from the tailplane tip to fuselage with a rod aerial under the starboard wing. Another important feature of the Griffon engine Spitfires was the entirely flush-riveted finish which was progressively introduced on all Spitfires.
The single-stage Griffon engine (II or IV) gave the aircraft superb low and medium level performance, although the Mk XII's performance declined at higher altitudes: because of this all production aircraft had "clipped" wings. In comparative tests with a Mk IX it was faster at sea level, but above it had become slower. Handling, however, was considered to be better than previous Spitfire marks, and the clipped wings conferred excellent manoeuvrability through enhanced aileron response.
At low altitude it was one of the fastest aircraft in the world; in one speed trial, held at Farnborough in July 1942 a prototype Mk. XII (DP845), piloted by Jeffrey Quill 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 dogfights with Spitfires of any type below . When the Mk XII was able to engage in combat it was a formidable fighter and several Fw 190s and Bf 109-Gs fell victim to it. The Mk XII's speed advantage at lower altitudes again became 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.
The first Griffon powered Spitfires suffered from poor high altitude performance due to having only a single stage supercharged engine. By 1943 Rolls-Royce engineers had developed 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 provided a substantial performance increase over the Mk IX 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.
The first batch of aircraft to fly with the Griffon 60 series engines were six converted Mk VIIIs JF316 to JF321 which were designated Mk VIIIG. The first one of these was flown by Jeffrey Quill on 20 January 1943:
One prototype, JF321, was fitted and tested with a Rotol six bladed contra-rotating propeller unit; although this promised to eliminate the characteristic swing on take-off (caused by the propeller slipstream) the propeller unit was prone to failure. The pitch control mechanism controlled the pitch on the front propeller;
The contra-rotating unit was later used on production Seafire 46 and 47s. When the new fighter entered service with 610 Squadron in January 1944 it signified a new leap forward in the evolution of the Spitfire. Jeffrey Quill flew the first production aircraft, RB140 in October 1943:
It could climb to in just over minutes and its top speed, which was achieved at , was .
F Mk XIVs had a total of 112 gallons of fuel consisting of 85 gallons in two main tanks and a 12.75 Imp. gal fuel tank in each leading edge wing tank. In addition 30 gallon and 90 gallon drop tanks could be carried. The fighter's maximum range was just a little over 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 an extra 75 gallons in two rear fuselage fuel tanks, extending the fighter's range to about on internal fuel. Mk XIVs with "tear-drop" canopies had 64 gallons. As a result, F Mk XIVs had a range that was increased to over .
Initially production rates were slow with only 341 being built until the end of 1944. The first test of the aircraft was in intercepting V1 flying bombs, and the Mk XIV was the most successful of all Spitfire marks in this role. The Spitfire XIV was also famous for being able to catch the notorious German jet, the Messerschmitt 262.The Mk XIV was used by the 2nd Tactical Air Force as their main high-altitude air superiority fighter in northern Europe with seven squadrons operational by May 1945. Spitfire XVIs also began to arrive in the CBI theatre in June 1945, too late to operate against the Japanese.
Late in 1944 a number of Mk XIVs were converted to have a single camera fitted, facing to port or starboard. To achieve this a new hatch, similar to the radio hatch on Merlin engine Spitfires, was installed. Otherwise this version of the FR Mk XVI was essentially the same as the standard aircraft. Later, purpose built conversions, also known as the F.R Mk XIV, had the cut down rear fuselage with its tear drop–shaped canopy, and a port facing fuselage camera, with an additional rear fuel tank of 34 gallons which extended the Spitfire's range to about on internal fuel. Because it was used mainly at low altitudes the FR Mk XIV had clipped wingtips.
In total, 957 Mk XIVs were built, over 430 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.
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 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.
300 F and F.R Mk 18s before production ended in early 1946
The Mk XIX was the last and most successful 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 (type 389s) 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. This version was the type 390.
The first Mk XIXs 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.
The second Mk XX, 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.
Aside from the more powerful engine, the Mk 21 had several notable features:
In other respects, the first production Mk 21s used the same basic airframe as the Mk XIV. The first true Mk 21 prototype, PP139 first flew in July 1943, with the first production aircraft LA187 flying on 15 March 1944. However the modifications over the Mk XIV left the aircraft over sensitive to trimming and LA201 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 wrote,
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. Jeffrey Quill was to write:
After intensive test flying the most serious problems were 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 with 91 Squadron. 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.
The Mk 22 was used by only one regular RAF unit, No. 73 Squadron RAF in the Middle East. However 12 squadrons of the Royal Auxiliary Air Force used the variant and continued to do so until March 1951.
The final Spitfire variant, the Mk 24, was similar to the Mk 22 except that it had an increased fuel capacity over its predecessors, with two fuel tanks of 33 gallons (150 l) each installed in the rear fuselage. There were also zero-point fittings for rocket projectiles under the wings. All had the larger "Spiteful" tail units: modifications were also made to the trim tab gearings in order to perfect the F 24’s handling characteristics. Late production aircraft were built with short-barrelled, electrically fired Mark V Hispano cannon.
Performance was impressive – the F 24 achieved a maximum speed of , and could reach an altitude of in eight minutes, putting it on a par with the most advanced piston-engined fighters of the era.
Although designed primarily as a fighter-interceptor aircraft, the Spitfire proved its versatility in several different roles. In fighter configuration the F 24’s armament consisted of four short-barrelled 20 mm Hispano cannon – operational experience had proved that the hitting power of these larger weapons was necessary to overcome the thicker armoured plating encountered on enemy aircraft as the war progressed. The aircraft also served successfully in the fighter-bomber role, being capable of carrying one and two bombs, with rocket-projectile launch rails fitted as standard.
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.
Introduced into service in 1946, the F. Mk 24 differed greatly from the original Spitfire Mk I in many respects and undoubtedly brought the design to the peak of perfection, being twice as heavy, more than twice as powerful and exhibiting an increase in climb rate of 80% over the prototype aircraft, 'K5054'. These remarkable increases in performance arose chiefly from the introduction of the Rolls-Royce Griffon engine in place of the famous Merlin of earlier variants. Rated at , the twelve-cylinder Vee liquid cooled Griffon 61 engine featured a two-stage supercharger, giving the Spitfire the exceptional performance at high altitude that had been sometimes lacking in early marks.