Supermarine Spitfire ( late Merlin - powered variants ) 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 problems for RAF fighter squadrons flying the latest Spitfire Mk Vb . By this time Rolls - Royce engineers were already working on a new version of the Merlin incorporating two - stage superchargers ; the combination of the improved Merlins and the Spitfire Mk VC airframe in a " stop - gap " design allowed the RAF to combat the Fw 190 on equal terms . In a second stream of development Supermarine was working on an improved , reinforced Spitfire airframe which incorporated several new features and was designed specifically for the Merlin 60 and 70 series engines . This new airframe later formed the basis for the Rolls - Royce Griffon powered Spitfires . This article presents a history of the Spitfire powered by two - stage engine variants and also describes some of the " drawing board " projects and experimental Spitfires . The Griffon powered variants are described in a separate article . Wing types . The majority of the Spitfires from the Mk VIII on , used three basic wing types ; C through to the E types C type . Also known as the " universal wing " the new design was standard on the majority of Spitfires built from mid 1942 . This wing was structurally modified to reduce labour and manufacturing time plus it was designed to allow mixed armament options ; A type , B type , or four 20 mm Hispano cannon . The undercarriage mountings were redesigned and the undercarriage doors were bowed in cross section allowing the legs to sit lower in the wells , eliminating the upper - wing blisters over the wheel wells and landing gear pivot points . Stronger undercarriage legs were raked 2 inches ( 5 . 08 cm ) forward , making the Spitfire more stable on the ground and reducing the likelihood of the aircraft tipping onto its nose . During production of the Mk VIII and Mk IX a new undercarriage leg was introduced which had external v - shaped " scissor - links " fitted to the front of the leg ; this also led to small changes in the shape of the undercarriage bay and leg fairings . Because the Spitfire was no longer to be used as a night fighter , the retractable landing lights were no longer fitted . The Hispano Mk IIs were now belt fed from box magazines allowing for 120 rpg ( the " Chattellerault " system ) . The fairings over the Hispano barrels were shorter and there was usually a short rubber stub covering the outer cannon port . Redesigned upper wing gun bay doors incorporated " teardrop " shaped blisters to clear the cannon feed motors , and the lower wings no longer had the gun bay heating vents outboard of the gunbays . The first series of Spitfire Mk IXs retained the bay doors first used on Spitfire VCs ; these incorporated large blisters to clear the feed motors of two Hispano cannons . All later Spitfires had smaller , more streamlined blisters . In order to provide room for the belt feed system of the cannon , the inner machine gun bays were moved outboard to between ribs 13 and 14 . Several versions of the Spitfire , starting with the HF Mk VIIs had extra 13 gallon integral fuel tanks added to the wing leading edges between the wing - root and the inboard cannon bay . Although many earlier Spitfires had been modified to carry bomb racks capable of carrying 250 lb ( 113 kg ) bombs the first Spitfires to be specifically modified for the fighter - bomber role ( known as Modification 1209 ) were those of the Second Tactical Air Force . The first Mk IX Spitfires started being used in the role in June 1944 . D Type . These were specifically made for the Photo - Reconnaissance Spitfires , including the PR Mk X and XI ; no armament was fitted and the " D " shaped leading edges of the wings , ahead of the main spar , were converted into integral fuel tanks , each carrying 66 gallons . To avoid the expansion of fuel in hot weather damaging the wing , pressure relief valves , incorporating small external vent pipes , were fitted near the wing tips . E type . Structurally unchanged from the C wing . The outer machine gun ports were eliminated , although the outer machine gun bays were retained and their access doors were devoid of empty shell case ports and shell deflectors . The inner gun bays allowed for two weapon fits ; or The . 303 machine guns mounted in the outer wings were no longer fitted as most aircraft at that time had armour impenetrable by . 303 bullets . During a turning combat the effectiveness of the outboard machine guns was low because if the aircraft was pulling ' g ' the flexing of the wings meant that the rounds scattered in a large cone . The 20 mm Hispano cannon were moved outboard and a more effective . 50 calibre Browning . 50 cal M2 / AN heavy machine gun with 250 rpg was added to the inner gun - bay . The first trial installation of the installation ( modification 1029 ) was made in " BS118 " in November 1943 ; by mid - March 1944 the first Spitfires to be modified were from 485 ( NZ ) , 222 and 349 Squadrons . Spitfires with this armament were referred to as " Spifire IX LF . 5 " and the E suffix was not officially introduced until early 1945 . This armament was standard for all Spitfire Mk IXs and XVIs used by the 2nd Tactical Air Force as fighters and fighter - bombers from shortly after D - Day . The improved armament was more effective for both air - to - air engagements and air - to - ground attacks . 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 " LF " versions , " e . g . " LF . IX . This designation referred to the low - altitude version of the Rolls - Royce Merlin engine , and , while many " LF " Spitfires had the " clipped " wings , a number did not . Variants . Mark numbers , type numbers . The Mark numbers did not necessarily indicate a " chronological " order ; for example , the Mk IX was a stopgap measure brought into production " before " the Mks VII and VIII . In addition , some Spitfires of one mark or variant may have been modified to another ; for example , several of the first Mk VBs were converted from Mk IBs ; the first Mk IXs were originally Mk VCs , converted , in some instances , by Rolls - Royce at their Hucknall facility . Up until the end of 1942 , the RAF designations always used Roman numerals for mark numbers . 1943 - 1948 was a transition period during which new aircraft entering service were given Arabic numeral s for 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 Mks I - XVI and Arabic numerals for the Mks 17 - 24 . " Type numbers " e . g . ; ( type 361 ) are the drawing board design numbers allocated by Supermarine . Features of late Merlin powered Spitfires . 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 . The longer Merlin 61 meant the nose forward of the engine / fuel tank bulkhead was 7 inches ( 17 . 8 cm ) longer . An intercooler was mounted behind the engine , on the supercharger casing . A small rectangular air scoop for a " Heywood " air compressor was fitted on the starboard upper engine cowling . The carburettor air intake on early to mid - production Spitfire IXs was a different shape to those of single - stage engined aircraft ; they were shorter and had a wider air inlet . From 1943 , an " Aero - Vee " tropical filter in a long , streamlined fairing was introduced for the carburettor air intake . This was fitted as standard to all Mk VIIs , VIIIs , PR Mk Xs and Mk XVIs , on mid to late production Mk IXs , and to most PR Mk XIs . A new 10 ft 9 in ( 3 . 27 m ) diameter four - bladed Rotol propeller was fitted , housed in a pointed spinner . The exhaust units were changed to six " fishtail " stacks per side . Under the nose , the three piece cowling was changed to a one piece layout . The oil tank was no longer a part of the cowling structure . Early Mk IXs had a teardrop shaped blister for a Coffman engine starter on the lower starboard side cowling , just behind the propeller . This was replaced by an improved electric starter on most two - stage Merlin powered Spitfires and , from late 1942 the blister was only seen on a few aircraft . The Type C wing was fitted as standard . Some mid and most late production Spifire Mk IXs and all Mk XVI were fitted with the Type E wing . While Spitfire IXs converted from Mk VCs had the large teardrop fairings on the upper surfaces , on the majority of Mk VIIs , VIIIs , IXs and XVIs the teardrop shaped blisters covering the Hispano feed motors were reduced in size and more streamlined than those on the Mk VC . According to A . P 1565J P & L ( Spitfire IX , XI and XVI Pilot ' s Notes ) the red painted undercarriage indicator rods , which projected through the tops of the wings when the undercarriage was down , were used only on early production Mk IXs . When fitted these rods supplemented an " Electric visual indicator " mounted on the instrument panel . The indicator rods seemed to be fitted on all Mk VIIs and VIIs , supplementing the electric visual indicator . A light for the retractable tailwheel was mounted on the instrument panel , just below the main visual indicator . Because the intercooler required a 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 the other half - radiator unit . When the engine was running at low speed , one radiator section provided enough coolant ; a thermostatic switch turned off the starboard radiator section until more power was called for and extra engine cooling was required . Other structural changes included flush riveting for the fuselage , introduced in mid - 1943 . A streamlined round rear - view mirror , with a bullet - shaped fairing replaced the rectangular version . On new production Mk IXs the small , teardrop shaped identification light behind the radio mast was removed . While early Mk IXs converted from Mk VCs had the original ( smaller ) elevator horn mass - balances , most had the enlarged version with the straightened leading edge . A new rudder of greater area , which could be identified by a " pointed " tip , was fitted to Mk VIIs , Mk VIIIs , and mid to late production Mk IXs and Mk XVIs . All Mk VII and Mk VIII Spitfires had the following changes : The internal structure was strengthened and revised . On the wings the ailerons were reduced in span by outboard of the outer hinges . There had been some instances of earlier models breaking up in the air in steep high speed dives , it was thought , because of aileron flutter . The main fuselage fuel tanks were increased in capacity ; 47 gal ( 213 . 7 l ) for the upper tank and 49 gal ( 222 . 7 l ) for the lower . In combination with the wing tanks this gave a total internal capacity of 122 gal ( 554 . 6 l ) , a near 50 % increase over the 85 gal ( 386 . 4 l ) carried by earlier Spitfire marks . In addition a 13 gal ( 64 l ) fuel tank was fitted in each wing leading edge between the wingroot and the inner gun - bay . The main undercarriage legs , for the first time in the Spitfire ' s life , were fitted with forward - facing torque links . In addition , the leg doors were slightly concave , allowing the undercarriage to sit lower in the wheel wells when retracted : this meant the upper wing skinning was free of the small bulge which had hitherto been necessary to clear the wheels . The wheels themselves were a new strengthened Dunlop AH10019 " four spoke " pattern , replacing the " five spoke " pattern used since the first Mk Is . This revised undercarriage was also fitted on some mid to late Mk IXs and all Mk XVIs . A retractable tailwheel ( Dunlop 2184 ) was fitted , covered by small doors when in flight . This also applied to the PR Mk Xs and most PR Mk XIs . Mk VII ( type 351 ) . Like the Mk VI , the Mk VII was a high altitude pressurised variant , this time powered by the Merlin 64 ( F . Mk . VII ) or 71 ( H . F . Mk . VII ) series engine with two - stage , two - speed superchargers . The cockpit was pressurised in a similar way to that of the Mk VI , although the details were slightly different . Other changes to the airframe are noted above . The Mk VII used a Marshall manufactured compressor for pressurising the cockpit ; this was mounted on the right of the engine and drew its air through a long intake under the starboard exhaust stubs . An automatic valve allowed a maximum pressure differential of + 2 lb . / sq . in . This was built up during the climb and was maintained at heights of 28 , 000 ft and above . 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 . While early Mk VIIs were fitted with a detachable canopy , secured by four pilot operated catches , later Mk VIIs were 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 . All were powered by the Merlin 64 ( F Mk VII ) or Merlin 71 ( HF Mk VII ) , the latter fitted with a Bendix - Stromberg " anti - g " carburettor . The HF Mk had superb high altitude performance , with a service ceiling of ; French ace Pierre Clostermann recalls in his book , " The Big Show " , the successful interception of a long - range reconnaissance Messerschmitt Bf 109G - 6 / R3 by a Mk VII " ' Strato Spitfire ' " of 602 Squadron at over the British Home Fleet ' s base at Scapa Flow in early 1944 . Mk VIII ( type 360 ) . 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 ; according to Supermarine ' s Chief Test pilot Jeffrey Quill " When I am asked which mark of Spitfire I consider the best from the flying point of view , I usually reply ' The Mark VIII with standard wingtips . ' I " hated " the extended wingtips . . . They were of no practical value to the Mark VIII and simply reduced the aileron response and the rate of roll . " 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 . The F Mk VIII ' s top speed was at 25 , 000 ft ( 404 mph for the LF . Mk VIII at and 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 for the HF Mk VIII ) . The two main tanks were given an extra 11 gal for a total of 96 gal which , along with the wing tanks , allowed the fighter to fly for a maximum distance of with a full internal fuel load and 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 , in the Pacific , with the Royal Australian Air Force and with the RAF 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 . Mk IX ( type 361 ) . 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 . The Air Ministry made the decision that Mk VC airframes should be converted to take the more powerful engine and , 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 . The first IX was a modified VC " AB505 " , which was tested by the Air Fighting Development Unit ( AFDU ) in April 1942 . The report said ; The performance of the Spitfire IX is outstandingly better than the Spitfire V especially at heights above 20 , 000 feet . On the level the Spitfire is considerably faster and climb is exceptionally good . It will climb easily to 38 , 000 feet and when levelled off there can be made to climb in stages to above 40 , 000 feet by building up speed on the level and a slight zoom . Its manoeuvrability is as good as a Spitfire V up to 30 , 000 feet and above is very much better . At 38 , 000 feet it is capable of a true speed of 368mph and is still able to manoeuvre well for fighting . 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 be an effective counter to the Focke Wulf Fw 190 . 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 IXs converted from VCs were stripped of armour , the . 303 Brownings and other equipment and repainted in a lightweight PRU blue finish . One of them 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 and large numbers of minor improvements were progressively introduced to Mk IXs , some of which were used on other Spitfire variants . The Merlin 61 was phased out early in 1943 in favour of the Merlin 63 and 63A . The new engine had increased power resulting from engine improvements and engine limitations of + 18 lbs . / sq . in and 3 , 000 rpm ( 5 minute combat ) . During the second half of 1943 , production of the Merlin 63 powered F Mk IX was discontinued in favour of the Merlin 66 powered LF Mk IX . Early production Spitfire IXs suffered from vapour locks in the fuel lines resulting from fuel evaporating if the aircraft was parked in direct sunlight . As a result of this the gun - camera was moved from the port wingroot to the starboard wingroot and a fuel cooler , fed by a small round air - intake was fitted in its place . This fuel cooler was also fitted to early PR Mk XIs Production of the LF Mk IXs , frequently referred to as the Spitfire IXB , initially ran in parallel with the Merlin 63 powered Marks . This version first became operational in March 1943 with the Biggin Hill Wing , comprised at the time of 611 and 341 ( Free French ) Squadrons . This type was by far the most produced of the Spitfire IX variants , with over 4000 built . The maximum power of the Merlin 66 was at 5 , 750 ft ( 1 , 283 kW at 1 , 752 m ) and the maximum speed of the Spitfire LF IX was at . The Merlin 66 introduced a new Bendix - Stromberg injection carburettor , which replaced the earlier S . U float carburettor . The H . F IX was powered by the specialised high altitude Merlin 70 and entered service in the Spring of 1944 . Serial listings show that the HF Mk IX was produced in relatively limited numbers when they were required , with priority being given to versions rated for low and medium altitudes Maximum power of the Merlin 70 was at 11 , 000 ft ( 1 , 275 kW at 3 , 353 m ) : maximum speed of the Spitfire HF . IX was at Also introduced in early 1944 was a new Mark II Gyro gunsight . This gunsight calculated the correct angle of deflection to use when leading the target . Its introduction doubled the effectiveness of RAF gunnery and was a major factor in Allied air superiority . The capacity of the main fuel tanks was 48 gal for the upper tank and 37 gal for the lower , for a total internal capacity of 85 gal . Jettisonable " slipper tanks " of 30 , 45 or 90 gal could be carried under the centre - section . As an alternative a cylindrical 50 gal drop tank , adapted from those carried by long range Hawker Typhoon s , could be carried on the fuselage bomb rack used on most Mk IXs of the Second Tactical Air Force . To further increase the combat radius some late production Mk IXs were fitted with additional internal self - sealing fuel tanks in the rear fuselage : the upper tank carried 41 gal and the lower 34 gal . When both were full this enabled a ferry range of over , although they made the aircraft unstable in flight and only straight flight and gentle manoeuvres at low altitudes were recommended by the pilot ' s manual . The pilot was also warned to avoid instrument flying whenever possible . Late production Mk IXs , in common with Mk XVIs introduced a new upper engine cowling which incorporated a distinct bulged top surface ; this design was adopted for the Mk XVI to allow for the modified intercooler of the Packard Merlin 266 , which had an integral header tank . The cut - down rear fuselage and bubble canopy , trialled on a Spitfire Mk VIII , was incorporated into very late production Mk IXs . With the cut down fuselage the lower forward fuselage tank capacity was increased to 47 gallons , while the rear fuel tanks were decreased to a capacity of 66 gallons . These were the rarest of the Mk IXs and many of them featured the " clipped " wings . The great majority of these saw postwar service with the SAAF , both in South Africa and in deployment in Korea during the 1950s . During early 1945 , some Spitfire IXEs and XVIEs of 74 Squadron were fitted with a single RP - 3 rocket under each wing . This was believed to be the only RAF Spitfire unit to use rockets operationally during the Second World War . PR Mk IX ( type 374 ) and FR Mk IX . Pending development of a dedicated Merlin 61 powered PR Spitfire ( the Mk XI ) at least three Mk IXs ( " BS338 " , " BS339 " and " BS473 " ) were taken off the production line and modified to carry two vertical cameras in the rear fuselage . The first of these was delivered to 541 Squadron at RAF Benson on 30 November 1942 . Subsequently another 15 Mk IXs were converted to PR Mk IXs ( factory designation type 374 ) at the Vickers - Armstrong Worthy Down facility . As well as incorporating camera equipment , a wrap - around PR type windscreen was fitted and a larger oil tank was installed under the nose . All armament was removed and a PRU Blue finish applied . These aircraft lacked the " wet wing " tanks , meaning that the PR Mk IX relied on drop tanks for extra range . The most famous PR Mk IX missions involved carrying out reconnaissance missions in preparation for Operation Chastise , the 617 " Dambusters " Squadron attacks on the Ruhr dams . A PR Mk IX photographed the dams the day before the operation and photographed the Moehne Dam after the operation . FR 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 and during Operation Market Garden . Another unit using FR Mk IXs was 318 ( Polish ) " City of Gdańsk " Fighter - Reconnaissance Squadron based in the Mediterranean . Some Spitfires in the MJ - and MK - serial ranges , sent for repair to the Forward Repair Unit ( FRU ) , were also converted by the FRU to a different style of FR Mk 9C with streamlined blisters on both sides of the fuselage . These were used exclusively by No . 414 Squadron RCAF to replace its TAC - R Mustangs . The same conversion was used on F Mk XIVE Spitfires to make FR Mk XIVE Spitfires used exclusively by No . 430 Squadron RCAF . T Mk IX and TR 9 ( type 509 ) . 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 . In total , 5656 Mk IXs were built , 561 by Supermarine and 5 , 095 by Castle Bromwich . 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 . PR Mk X and PR Mk XI ( types 387 , 365 and 370 ) . When development started on new Merlin 60 powered Spitfires , both the Mk VII and VIII were to have photo - reconnaissance ( PR ) variants . On 21 April 1942 , an order was placed for 70 aircraft , provisionally designated PR Mk VIII . Based on the revised MK VIII airframe these aircraft were to be powered by Merlin 61s and were assigned serial numbers " LV643 - 681 " and " LV726 - 756 " . The Spitfires bearing these serials were eventually built as Merlin 66 LF Mk VIIIs . A policy change resulted in the pressurised PR variant of the Mk VII being renamed PR Mk X ( type 387 ) . This version followed the PR Mk XI into production and was based on the Mk VII airframe with PR Mk XI wings and camera installation . It had the pressurised Mk VII cockpit , with the Lobelle sliding canopy , and retained the fighter style windscreen with the bullet - proof glass panel . The long thin air intake to the cockpit pressurisation system was fitted under the exhaust stacks on the starboard cowling . The performance was similar to that of the PR XI although the pressurised cockpit meant that this version could stay at altitudes of over 40 , 000 ft for longer without the exhausting physiological effects experienced by the pilots of unpressurised cockpits . Sixteen Mk Xs were built during April and May 1944 , with the first mission being flown on 11 May . All saw limited service in 541 and 542 Squadrons in a high altitude reconnaissance role . Experience with this version led to the development and production of the pressurised version of the PR Mk XIX . The Mk XI ( type 365 standard , type 370 tropicalised ) was based on a combination of features from the marks VII , VIII and IX . The Mk XI was the first PR variant to have the option of using two vertically mounted F52 cameras with 36 - inch - focal - length lens in the fuselage behind the cockpit . Several other configurations could be fitted , depending on mission requirements ; the " X Type " installation , for example had two vertically mounted F24s with 14 - inch lens and an oblique F24 with an 8 - inch lens mounted above and facing to port . PR Mk XIs used for tactical reconnaissance had an additional , vertically oriented camera in a fairing under each wing . Physically the Mk XIs had a deeper nose fairing to accommodate a larger 14 . 5 gal oil tank and used the unarmoured , wrap - around PRU windscreen . " Booster " pumps for the wing tanks were fitted and covered by " teardrop " shaped fairings under the wings . Retractable tailwheels were fitted as standard and the majority of the Mk XIs built had the later large - area " pointed " rudder . 260 Mk XIs were powered by Merlin 61 , 63 or 63A engines , while the remaining 211 used the high - altitude Merlin 70 . All of the Merlin 70 and 198 of the Merlin 60 series aircraft were fitted with the Vokes Aero - Vee dust filter in the extended , streamlined carburettor air intake under the nose . All Merlin 60 powered aircraft featured the fuel cooler in the port leading edge wing root . The radio installation was either the VHF TR . 1133 or TR . 1143 fitted with the " Rebecca " beam approach equipment . Additional " slipper " drop tanks could be fitted under the centre - section ; in common with the Mk IX these could be 30 , 45 or 90 gal capacity and , for the Mk XI , a tank of 170 gal capacity was also available . Spitfire PR Mk XIs were capable of a top speed of at and could cruise at at . Normally Spitfire XIs cruised between these altitudes although , in an emergency , the aircraft could climb to However , pilots could not withstand such altitudes for long in a non - pressurised cockpit without suffering from serious physiological effects . At first , production of the PR Mk XI was delayed because development of the Mk VII and VIII series was delayed . As a result it was decided to base the Merlin 60 powered PR aircraft on the MK IX airframe . Production was further threatened because of a dispute over RAF PR doctrine : in early 1943 , because the new PR Spitfire was delayed , the Air Ministry proposed that all PR units be converted to de Havilland Mosquito es . After further analysis the Air Staff agreed that Mosquitoes could perform 90 % of PR missions so the Spitfire production for only 10 % of PR units was mooted . Air Vice Marshal John Slessor , head of Coastal Command pointed out that the Spitfire was smaller than the Mosquito , used half the number of Merlin engines and was faster , more manoeuvrable and quieter and , therefore production should be increased , not reduced . As a result the Air Staff decided that PR Mk XI production should be accelerated at the cost of the fighters . The first Mk XIs were built in November 1942 : from April 1944 production ran concurrently with the PR Mk XIX before ending in December 1944 , when they were phased out in favour of the Mk XIX . In total 471 Mk XI were built by Supermarine . PR Mk XIII . The PR Mk XIII was an improved PR Type G with a single - stage Merlin engine and is described in Supermarine Spitfire ( early Merlin powered variants ) Mk XVI ( type 361 ) . 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 prefix 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 and were fitted with the rear fuselage fuel tanks with a combined capacity of 75 gal . Many XVIs featured cut - down rear fuselages with " bubble " canopies . On these aircraft the rear fuselage tank capacity was limited to 66 gal . 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 2 × 20 mm Hispano II cannon - each with 120 rpg - and 2 × . 50 calibre Browning machine guns - each with 250 rpg . 1 × 500 lb ( 227 kg ) bomb could be carried underneath the centre rack , and 1 × 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 . Spitfire Floatplanes ( types 355 & 359 ) . 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 / 7 scale model , it was found that the concept was basically sound , although the vertical tail surfaces would need to be enlarged to counterbalance 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 without being flown 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 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 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 / s 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 : Soon after testing started the idea of using floatplane fighters was dropped and " MJ982 " was converted back to a landplane . Five aircraft were converted : Griffon engine variants . The early Rolls - Royce Griffon powered Spitfire variants were adaptations of Mk VC ( early Mk XII ) or Mark VIII ( late Mk XII and Mk XIV ) airframes . The later Griffon engined Spitfire variants embodied new wings , tail units and undercarriages and were very different from any of the earlier Spitfire marks . Because of this the Griffon engined variants are described in a dedicated article . Production . After the destruction of the main Itchen and Woolston works by the " Luftwaffe " in September 1940 , all Supermarine manufactured Spitfires were built in a number of " Shadow Factories " ; by the end of the war there were ten main factories and several smaller workshops which built many of the components . A fuller explanation can be found in Supermarine Spitfire . The main Castle Bromwich factory was also aided by a smaller number of the shadow factories . The breakdown of production figures is taken from " Air International 1985 , p . 187 . " Information as to when the first production aircraft emerged is from the serial number lists provided in " Morgan and Shacklady 2000 " . Because the first of the Mk IXs were converted from Mk VCs the first true production Mk IX is listed by serial Number .