Supermarine Spitfire variants part one

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File:Spitfire F VB BM597.jpg

Spitfire Mk VB BM579 of Duxford's Historic Aircraft Collection in the markings of 317 (Polish) "Wileński" Squadron.

The British Supermarine Spitfire was an outstanding fighter aircraft of the Second World War. The basic airframe proved to be extremely adaptable, capable of taking far more powerful engines and far greater loads than its original role as a short-range interceptor had allowed for. This would lead to 24 marks of Spitfire, and many sub-variants within the marks, being produced throughout the Second World War and beyond, in continuing efforts to fulfill Royal Air Force requirements and successfully combat ever-improving enemy aircraft. It is notable that throughout the entire development process, which took place over twelve years, from 1935 through to 1948, there were no outstanding failures of the basic design: this is a real testament to the original genius of Reginald J. Mitchell, his successor Joseph Smith, and the design teams they led.

These articles present a brief history of the Spitfire through all its variants. Part one deals with Spitfires powered by Single-Stage Rolls-Royce Merlins. Part two continues with those Spitfires powered by Two-Stage Merlins and Rolls-Royce Griffon engines.

Spitfire
275px
Spitfire Vc launching from USS Wasp
Type	Fighter
Manufacturer	Supermarine
Designed by	R. J. Mitchell
Maiden flight	5 March 1936
Retired	1955, RAF
Primary user	Royal Air Force
Produced	1938–1948
Number built	20,351
Variants	Seafire Spiteful

Wing types

The Spitfires with the Single Stage Merlin engines used four different wing types, A through to D which had the same dimensions and plan but different internal arrangements of armament and fuel tanks. All Mk Is, II, and Vs had small, rectangular undercarriage indicator pins which projected at an angle from the upper wing surfaces when the undercarriage legs were locked down. These supplemented lights on the instrument panel.

• A type: The original wing design, the basic structure of which was unchanged until the C type in 1942. The one major alteration made to this wing, soon after production started was the incorporation of heating for the gun bays: open structures around the gun-bays were blocked off. Ducting, drawing hot air from the back of the radiators, was added to the wings. The heated air was exhausted through underwing vents, covered by streamlined triangular blisters, just inboard of the wingtips. Towards the end of 1940 the fabric covered ailerons were replaced by ones covered in light-alloy. The only armament able to be carried was eight .303 inch Browning machine guns with 300 rpg.
• B type: This was the A type modified to carry a 20mm Hispano cannon. The retractable underwing landing lamp was repositioned and the innermost m.g bays were replaced with a single cannon bay, plus a compartment for the drum magazine outboard of the wheel well. The upper and lower wing skins incorporated blisters to clear the ammunition drum. Under the wings there were two possible blister shapes. The alloy covered ailerons were standardised on this wing type.

One type of armament could be fitted:

• Two 20 mm Hispano Mk II cannon, drum magazines with 60 rounds/gun.
• Four .303 Browning mgs with 350 rounds/gun.

• C type: "Universal wing". The wing was structurally modified to reduce labour and manufacturing time plus allowing 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.
• The 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 it's nose.
• The Hispano Mk IIs fitted in all cases were now belt fed from box magazines allowing for 120 rounds each (the "Chattellerault" system). The fairings over the Hispano barrels were shorter and there was usually a short rubber stub covering the outer cannon port.
• The redesigned upper wing gun bay doors incorporated blisters to clear the cannon feed motors, and the lower wings no longer had the gun-bay heating vents outboard of the gunbays.
• The inner machine gun bays were moved outboard to between ribs 13 and 14.
• The retractable landing lights were no longer fitted.
• There were strong-points added outboard of the wheel-wells capable of taking a 250 lb (113 kg) bomb under each wing.
• Several versions of the Spitfire, starting with the H.F Mk VIIs had extra 14.5 imp gallon integral fuel tanks added to the wing leading edges between the wing-root and the inboard cannon bay.

In practice, most aircraft carried the two 20mm Hispano IIs with 120 rpg and 4 .303 Browning mgs with 350 rpg. Several Spitfire Vcs which were transported to Malta were initially fitted with four Hispanos, although they soon reverted to the standard B type configuration.

• D type: unarmed long-range wing for reconnaissance versions with the D shaped wing structure ahead of the main spar converted to integral fuel tanks capable of carrying 66 Imperial gallons (300 liters).

Starting with the Mk V some Spitfires had their rounded wingtips replaced by shorter, squared off fairings to improve low-altitude performance and enhance the roll rate. These are sometimes referred to as "L.F" versions, e.g. L.F.Vb. 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.

Single-Stage Merlin Engine Variants

Note:

• The Mark numbers did not necessarily indicate a chronological order; for example, the Mk IX was a stopgap measure brought into production before the marks VII and VIII.
• 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.
• Up until the end of 1942, the RAF always used Roman numerals for mark numbers. 1943 to 1948 was a transition period during which new aircraft entering service were given Arabic numerals 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 marks I through XVI and Arabic numerals for the marks 17 through 24.
• Type numbers eg; (type 361) are the drawing board design numbers allocated by Supermarine.
• All liquid capacities and measurements are in Imperial units.

Prototype K5054 (Type 300)

File:Supermarine Spitfire Protoype K5054 Unpainted.jpg

The unpainted Spitfire prototype K5054 at Eastleigh airfield, just before the first flight. The angled rudder mass balance, fixed, unfaired main undercarriage and tailskid can be seen.

Construction on K5054 started in December 1934. Several modifications were incorporated into the prototype as construction continued. At the time of her first flight on 5 March 1936 K5054 was unpainted and the undercarriage had no fairings fitted and was fixed down. A tailskid was fitted under the rear fuselage. The cowling panels were noticeably lighter in tone than the rest of the airframe. A prototype Merlin C engine of 990 hp (738 kW), with six flush-fitting exhaust ports each side was fitted. This power unit drove an Aero-Products "Watts" two-bladed, wooden fixed-pitch propeller. The rudder mass balance was larger than that of production aircraft, with an angled lower edge cutting further into the top of the tailfin. Although the basic wing planform was to stay the same for most production Spitfires, the prototype wing was structurally different. No weapons were fitted and the alclad skinning was laid out in spanwise strips. Underneath the wings the radiator bath started immediately behind the starboard undercarriage bay, with the opening conforming to the angle of the bay. The wingtips were an integral part of the structure, unlike production aircraft. A long pitot tube projected from near the port wingtip.

Mk I (type 300)

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K9795, the 9th production Mk I, with 19 Squadron, showing the wooden, two-blade, fixed-pitch propeller, early "unblown" canopy and "wraparound" windscreen without the bullet proof glass plate. The original style of aerial mast is also fitted.

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 Woolston and, only a few months later, another 450. This brought the total to 2,160, making it one of the largest orders in RAF history.

The Woolston line started delivering the Mk I Spitfire in late 1937 with front-line service commencing in August 1938. Over the next three years a large number of modifications were made, especially as a result of wartime experience:

• The early Mk Is were powered by the 1,030 hp (768 kW) Merlin Mk II engine driving an Aero-Products "Watts" 10 ft 8 in (3.3 m) diameter two-blade wooden fixed-pitch propeller, weighing 83 lb (38 kg).

The Merlin I to III series all relied on external electric power to start the engine; a well known sight on RAF fighter airfields was the "trolley acc" (trolley accumulator) which was a set of powerful batteries which could be wheeled up to aircraft. The lead from the "Trolley Acc" was plugged into a small recess on the starboard side cowling of the Spitfire. On Supermarine built aircraft a small brass instruction plate was secured just beneath.

• Early on in the Spitfire's life it was found that at altitudes above about 15,000 ft (4572 m), any condensation could freeze in the guns. The system of gun heating, described above, was introduced on the 61st production Mk I.
• At the outset of World War 2, the flash-hiders on the gun muzzles were removed and the practice of sealing the gun ports with fabric patches was instituted. The patches kept the gun barrels free of dirt and debris and allowed the hot air to heat the guns more efficiently. When the guns were fired the patches were shot through, and were always replaced by the ground-crew during rearming.
• The Aero Products propeller was replaced by a 350 lb (183 kg) de Havilland 9 ft 8 in (2.97 m) diameter, three-bladed, two-position, metal propeller, which greatly improved take-off performance, maximum speed and the service ceiling. It also started the incremental weight increases which continued through the life of the airframe.
• The manual hand-pump for operating the undercarriage was replaced by a motorised hydraulic system.
• From the 175th production aircraft, Merlin Mk III, which had a "universal" propeller shaft able to take a de Havilland or Rotol propeller was fitted.
• Just before the Battle of Britain, a de Havilland constant speed propeller, of the same diameter as the two-position unit, became available. Although this was a great deal heavier than the earlier types (500 lb (227 kg)) it gave another substantial improvement in take-off distance and climb rate.

File:Spitfire1602a.jpg

A Spitfire Mk Ia of 602 Squadron in early 1940. A de Havilland 3 blade propeller unit is fitted, along with a "blown" canopy and the laminated bullet proof windscreen and later aerial mast. The brass plate below the external starter plug can be seen on the side engine cowling.

• A simplified design of pitot tube was introduced.
• The "rod" aerial mast was replaced by a streamlined, tapered design.
• Following complaints from pilots a new form of "blown" canopy was manufactured and started replacing the original "flat" version in early 1939. This canopy improved headroom and enabled better vision laterally, and to the rear.
• Small rear view mirrors were added to the windscreen: an early "shrouded" style was later replaced by a simplified, rectangular, adjustable type.
• A thick, laminated glass, bullet proof plate was fitted to the curved, one piece windscreen.
• A 3mm thick cover of light alloy was fitted over the top of the two fuel tanks.
• From about mid 1940, 73 pounds (33 kg) of armoured steel plating was provided in the form of head and back protection on the seat bulkhead and covering the forward face of the glycol header tank.
• "Two step" rudder pedals, which were fitted to all frontline Spitfires just before the Battle of Britain: these allowed the pilot to lift his feet and legs higher during combat, improving his "blackout" threshold and allowing him to pull tighter sustained turns.
• Starting in September 1940, IFF equipment was installed. This weighed about 40 lb (18 kg) and could be identified by wire aerials strung between the tailplane tips and rear fuselage. Although the added weight and the aerials reduced maximum speed by about two mph three km/h), it allowed the aircraft to be identified as "friendly" on radar: lack of such equipment was a factor leading to the Battle of Barking Creek.

• At about the same time new VHF T/R Type 1133 radios started replacing the HF TR9 sets. These had first been fitted to Spitfires of 54 and 66 Squadrons in May 1940, but ensuing production delays meant the bulk of Spitfires and Hurricanes were not fitted for another five months. The pilots enjoyed a much clearer reception and were a big advantage with the adoption of Wing formations throughout the RAF in 1941. The new installation meant that the wire running between the aerial mast and rudder could be removed, as could the triangular "prong" on the mast.

Weight increases and aerodynamic changes led to later Spitfire Is having a lower maximum speed than the early production versions. This was more than offset by the improvements in take-off, climb rate and ceiling brought about by the two-position and constant speed propeller units.

At the start of the war the engine ran on the then-standard 87 octane aviation spirit. From March 1940 increasing quantities of 100 octane fuel, imported from the U.S., became available. This meant that during the defensive battles over Dunkirk the Spitfire Is benefited from an allowable increase in supercharger "boost" from 6 lbs to 12 lbs without damaging the engine. With the 12 lb "emergency boost", the Merlin III was able to generate 1,305 hp (973 kW) in a five minute burst.

File:19sqdn-spit1-1.jpg

X4474, a late production Mk I of 19 Squadron flown by Sergeant Jennings in September 1940. This photo makes a good comparison with K9795.

• From November 1940, Supermarine started producing light-alloy covered ailerons which quickly replaced the original fabric covered versions. From this time on, alloy ailerons were fitted to all Spitfires coming off the production lines.
• 19 Squadron received several Spitfires armed with two Hispano 20mm cannon during the Battle. These were known as the Mk IB, the eight machine gun Mk Is were retrospectively called the Mk Ia. With the early cannon installation, jamming was a serious problem. In one engagement, only two of the 12 aircraft had been able to fire off all of their ammunition. Further cannon-armed Spitfires, with improvements to the cannon mounts, were later issued to 92 Squadron and it was eventually realised the best armament mix was two cannon and four machine guns (most of these were later converted to the first Mk Vb).

Foreign orders: Mk Is

The type numbers 332, 335, 336 and 341 were given to versions of the Mk I which were to be modified to meet the requirements of Estonia, Greece, Portugal, and Turkey respectively. Estonia's order was cancelled when the Soviet Union annexed the country. The Greek and Portuguese orders were refused by the Foreign Office. The 59 aircraft for Turkey were approved, but after delivering two aircraft, the Foreign Office put a halt to that too in May 1940.

The 208th production Spitfire I was sold to France and in June 1939 was delivered for evaluation.

In 1941, the British government agreed to supply Portugal with 18 Spitfire Mk 1as. These were refurbished aircraft, drawn from RAF stocks, retrofitted with TR 9 HF radios and no IFF. These arrived from late 1942 and were given the serial numbers 370 to 387, forming the XZ Esquadrilha at Tancos. These were all scrapped by the end of 1947.

Speed Spitfire (type 323)

In late 1938, a standard Mk I K9834 was taken off the production line and modified for an attempt on the World Speed Record.

A special "sprint" version of the Merlin II driving a Watts small diameter, coarse pitch, four bladed wood propeller was able to generate 2,160 hp (1,611 kW) for short periods. Smaller fuel and glycol header tanks were fitted, in the expectation any record attempts would be of short duration. The wingspan was reduced to 33 ft 7 in (10.26 m), with the wingtips being rounded, and the radiator housing under the wing was increased in size. All military equipment was removed.

All panel lines were filled and smoothed over, all round headed rivets on the wing surfaces were replaced by flush rivets and an elongated "racing" windscreen was fitted. A tailskid replaced the tailwheel. Finally the "Speed Spitfire" was painted in a highly polished gloss Royal Blue and Silver finish. As it turned out the finished aircraft actually weighed some 298 lb (135 kg) more than a standard 1938 vintage Spitfire.

Once the World Speed records were broken in quick succession, first by the Messerschmitt Bf 109 V13 and then by the Heinkel He 100 and Messerschmitt Me 209, it was decided the Speed Spitfire needed a great deal more modification to even come close to the new speed records and the project lapsed.

On the outbreak of War, the Speed Spitfire was modified to a hybrid PR Mk II with the special Merlin II being replaced by a Merlin XII driving a variable pitch de Havilland propeller, and the racing windscreen replaced by a PR wrap-around type. Nothing could be done about the reduced fuel capacity and it could never be used as an operational aircraft. Flown as a liaison aircraft between airfields in Britain during the war, K9834 was scrapped in June 1946.

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. It was soon found that modified Blenheims and Lysanders were easy targets for German fighters and heavy losses were being incurred whenever these aircraft ventured over German territory.

In October 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 armament and radios removed and replaced with extra fuel and cameras. As a result of his representations two Spitfires N3069 and N3071 were released by Fighter Command and sent to the "Heston Flight", a highly secret reconnaissance unit under the command of Wing Leader Sidney Cotton. These two Spitfires were "Cottonised" by stripping out the armament and radio-transmitter, then, after filling the empty gun ports and all panel lines, the airframe was rubbed down to remove any imperfections. Coats of a special very pale blue-green called Camoutint were applied and polished. Two two F .24 cameras with five inch focal length lenses which could photograph a rectangular area below the aircraft were installed in the wing space vacated by the inboard guns and their ammunition containers as a stop-gap measure. Heating equipment was installed on all P.R Spitfires to stop the cameras from freezing and the lenses from frosting over at altitude. These Spitfires, which later officially became the Spitfire Mk I P.R Type A, had a maximum speed 10 to 15 mph (16 to 24 km/h) faster than that of the fighter.

By January 1940, after several high-altitude missions by No. 2 Camouflage Unit (as Heston Flight was renamed, to explain the unusual colour scheme of its aircraft) proved the concept, further Spitfires were delivered and modified, becoming the first of the well established line of unarmed, high speed photo reconnaissance aircraft.

The original reconnaissance models were based on the Mk. I as follows; the majority of those built were conversions of existing fighter airframes.

• Two Mk I PR type A The original conversions described above.
• In the Mk I PR Type B the camera lenses were upgraded to an eight 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.
• It had been envisaged that much larger cameras would be installed in the fuselage immediately behind the pilot, but at the time RAF engineers believed this would upset the Spitfire's centre of gravity. Cotton was able to demonstrate that by removing lead weights, which had been installed in the extreme rear fuselage to balance the weight of the constant speed propeller units, it was possible to install cameras with longer focal-length lens in the fuselage.
• The Mk I PR Type C carried more fuel 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 in a blister tank under the port wing, which was counterbalanced by a camera installation on the starboard wing.
• The Mk I PR Type D carried so much fuel that it was nicknamed "the bowser." The D shaped wing leading edges, ahead of the main spar, proved to be an ideal location for an integral tank . Accordingly, in early 1940, work started on converting the leading edges, between rib four through to rib 21, by sealing off the spar, outer ribs and all skin joins allowing 57 gallons (259 l) of fuel to be carried in each wing. Because the work was of low priority, and with the urgent need for fighters the first two, hand-built prototypes of the PR Type Ds weren't available until October. In addition to the leading edge tanks these prototypes also had a 29 gallon (132 l) tank in the rear fuselage. An additional 14 gallon (63 l) oil tank was fitted in the port wing. The cameras, two vertically mounted F.24s with 8 inch (20.3 cm) or 20 inch (50.8 cm) lens or two vertically mounted F.8s with 20 inch lens, were located in the rear fuselage. With the full fuel load the center of gravity was so far back the aircraft was difficult to fly until the rear fuselage tank had been emptied. Despite these difficulties the type quickly proved its worth, photographing such long distance targets as Stettin, Marseilles, Trondheim and Toulon.
• Once the first two Type Ds, P9951 and P9952 had proven the concept the production aircraft were modified to increase the leading edge tank capacity to 66.5 gallons (302 l) and by omitting the rear fuselage tank. These aircraft were better balanced and had the more powerful Merlin 45 engine as used by the Mk V, along with heated cabins, which were a great comfort to pilots on such long flights. A total of 229 Type Ds were built.
• The Mk I PR Type E 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 Mk I PR Type F was an interim "super-long-range" version which entered service in July 1940, pending the Type D. The Type F carried a 30 gallon fuel tank under each wing, plus a 29 gallon tank in the rear fuselage, as well as having an enlarged oil tank under the nose. 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. 15 of these were based on the Mk V airframe.
• The Mk I PR Type G performed a similar role to the Type E. The Type G was much more closely related to the fighters, being fully armed with eight .303 Brownings and having the armoured windscreen. One oblique and two vertical cameras were installed in the fuselage, as well as a 29 gallon (132 l) fuel tank just behind the pilot.

Also new to PR Spitfires were the "blown" canopies which incorporated large lateral teardrop shaped blisters, allowing the pilots a much clearer view to the rear and below, vital for sighting the cameras. On all unarmed P.R conversions the gunsight was replaced by a small camera control box from which the pilot could turn the cameras on, control the time intervals between photos and set the number of exposures.

In 1941 a new system of mark numbers was introduced, independent of those used for the fighter versions:

• The Type C became the PR Mk III.
• The Type D became the PR Mk IV.
• The Type E became the PR Mk V.
• The Type F became the PR Mk VI.
• The Type G became the PR Mk VII.

In all, 1,567 Mk Is were built (1,517 by Supermarine between May 1938 and March 1941, 50 by Westland, July to September 1941).

Mk II (type 329)

File:Spitfire IIA P7350.jpg

Spitfire Mk IIa P7350 of the Battle of Britain Memorial Flight. P7350 first entered service with 266 Squadron in August 1940, and was then handed over to 603 squadron in October 1940, the markings in which she is now painted.

In the summer of 1939 an early Mk I K9788 was fitted with a new version of the Merlin, the XII. With the success of the trial it was decided to use this version of the Merlin in the Mk. II which, it was decided, would be the first version to be produced exclusively by the huge new Nuffield "shadow" factory at Castle Bromwich.

Chief among the changes was the upgraded 1,175 hp (876 kW) Merlin XII engine. This engine included a Coffman cartridge starter, instead of the electric system of earlier Merlins and it required a small "teardrop" blister on the forward starboard cowling. The Merlin XII was cooled by a 70% to 30% water glycol mix, rather than pure glycol used for earlier Merlin versions.

In early 1940 Spitfire Is of 54 and 66 Squadrons were fitted with Rotol manufactured wide-bladed propellers of 10 ft 9 in (3.27 m) diameter, which were recognisable by a bigger, more rounded spinner: the decision was made that the new propeller would also be used exclusively by the Mk II. This engine/propeller combination increased top speed over the late Mk. I by about 6-7 mph below 17,000 feet, and improved climb rate.. Due to all of the weight increases maximum speed performance was still lower than that of early Mk. Is, but combat capability was far better.

The Mk II was produced in 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 Operational Training Units. The RAF had re-equipped with the new version by April 1941.

• A small number of Mk IIs were converted to "Long Range" Spitfires in early 1941. These could be recognised by the fixed 40 gallon (182 litre) fuel tank which was fitted under the port wing. With a full tank manoeuvrability was reduced, maximum speed was 26 mph (42 km/h) lower and the climb rate and service ceiling were also reduced. Several squadrons used this version to provide long-range bomber escort.
• Once the Mk II was taken out of frontline service 50 of them were converted for air-sea rescue work, at first under the designation Mk IIC (type 375) but later referred to as the A.S.R Mk II. The Merlin XII was replaced by the Mark XX, a "rescue pack" was fitted in the flare chute and smoke marker bombs were carried under the port wing.

A total of 921 Mk IIs were built, all by Castle Bromwich.

Mk III (type 330)

The Mk. III was the first attempt to improve the basic Spitfire design and introduced several features which were used on later marks. Powered by a Rolls Royce Merlin XX developing 1,390 hp (1,036 kW) the wingspan was reduced to 30 ft 6 in (9.3 m) and the area reduced to 220 square feet (20.4 sq m) while the overall length was increased to 30 ft 4 in (9.2 m). The strengthened main undercarriage was raked forward two inches, increasing ground stability and had flaps to fully enclose the wheels when retracted. The tailwheel was also made fully retractable. The windscreen was redesigned, with a built-in, internal laminated glass, bullet proof panel and optically flat, laminated glass quarter panels.

Only one Mk. III N3297 was built and first flown on 16 March 1940. Although the new Spitfire was developed to replace the earlier marks on the production lines, a decision to allocate the limited supplies of Merlin XX to the Hurricane II series meant that the Mark III lapsed. Priority then focused on the Mark V series.

N3297 became the power-plant development airframe, the wings were replaced with standard Type A and the aircraft was delivered to Rolls Royce at Hucknall. A prototype Merlin 61 was installed, in effect making this aircraft (renumbered the type 348) the prototype Mk IX.

Mk V (type 331)

File:Spitfire V 316.jpg

Polish Vb from 303 Kościuszko Squadron flown by S/Ldr Zumbach. The early style windscreen has the rear view mirror on the lengthened mounting used by this unit.

Late in 1940, the RAF predicted that the advent of the pressurised Junkers Ju 86P bomber series over Britain would be the start of a new sustained high altitude bombing offensive by the Luftwaffe, in which case development was put in hand for a pressurised version of the Spitfire, with a new version of the Merlin (the Mk VI). It would take some time to develop the new fighter and an emergency stop-gap measure was needed as soon as possible: this was the Mk V.

The basic Mk V was a Mk I with the Merlin 45 series engine. This engine delivered 1,440 hp (1,074 kW) at take-off, and incorporated a new single-speed single-stage supercharger design. Improvements to the carburettor also allowed the Spitfire to use zero gravity manoeuvres without any problems with fuel flow. Several Mk I and Mk II airframes were converted to Mk V standard by Supermarine and started equipping fighter units from early 1941. The majority of the Mk Vs were built at Castle Bromwich.

Three versions of the Mk V were produced, with several sub-series:

• Mk Va: Continued with the Type A wing with the eight .303 Brownings. This version could reach a top speed of 375 mph (603 km/h) at 20,800 ft, and could climb to 20,000 ft in 7.1 minutes. A total of 94 were built. (One well known Va was W3185 D-B flown by Douglas Bader when commanding the Tangmere Wing in 1941.)

• Mk Vb: The Vb became the main production version of this variant. Along with the new Merlin 45 series the B wing was fitted as standard. As production progressed changes were incorporated, some of which which became standard on all later Spitfires. Production started with several Mk Ibs which were converted to Mk Vbs by Supermarine:
• The round section exhaust stacks were changed to a "fishtail" type, marginally increasing exhaust thrust. Some late production Vb and Vc were fitted with six shorter exhaust stacks per side, similar to those of Spitfire IXs and Seafire IIIs.
• After some initial problems with the original Mk I size oil coolers, a bigger oil cooler was fitted under the port wing; this could be recognised by a deeper housing with a circular entry.

File:Spitty with clipped wings.jpg

Spitfire L.F Mk. Vb of 316(Polish) "Warszawski" Squadron. This Spitfire has the wide bladed Rotol propeller, the internal armoured windscreen and "clipped" wings.

• Many Spitfires in the Mk V and Mk IX family used wheels which had a removable disc type hub fitted.
• Two new "blown" cockpit canopies were introduced in an effort to further increase the pilot's head-room and visibility.
• Many Spitfire Vbs were fitted with "gun heater intensifier" systems on the exhaust stacks. These piped additional heated air into the gun bays. There was a short tubular intake on the front of the first stack and a narrow pipe led into the engine cowling from the rear exhaust.
• The Spitfire Vb series were the first Spitfires able to carry a range of specially designed "slipper" drop tanks which were fitted underneath the wing centre-section. Small hooks were fitted, just forward of the inboard flaps: when the tank was released these hooks caught the trailing edge of the tank, swinging it clear of the fuselage.
• A wide bladed Rotol constant speed propeller of 10 ft 10 in (3.29 m) diameter was able to be fitted, superseding the de Havilland unit. The "Jablo" blades were made out of compressed wood and the spinner was longer and more pointed.
• This was the first production version of the Spitfire to use "clipped" wingtips as an option, reducing the wingspan to 32 ft 2 in (9.8 m). The clipped wings increased the roll rate at lower altitudes.
• Several different versions of the Merlin 45/50 family were used, including the Merlin 45M which had a smaller "cropped" supercharger impeller and boost increased to +18 lb. This engine produced 1,585 hp (1,182 kW) at 2,750 ft (838 m), increasing the L.F Vb's maximum rate of climb to 4270 ft/min (21.6 m/sec) at 3850 ft.

File:Spitvbtropvo.jpg

Spitfire VC Trop, fitted with Vokes filters and "disc" wheels, of 417(RCAF) Squadron in Tunisia in 1943.

• The tropical version of the Mk Vb could be identified by the large Vokes air filter fitted under the nose; the reduced speed of the air to the supercharger had a detrimental effect on the performance of the aircraft. It was also fitted with desert survival gear behind the pilot's seat.
• Many Vb Trops were modified by RAF Depots in Egypt by replacing the Vokes filter with locally manufactured "Aboukir" filters, which were lighter and more streamlined. Two designs of these filters can be identified in photos: one had a bulky, squared off filter housing while the other was more streamlined. These aircraft were usually fitted with the wide blade Rotol propeller and clipped wings.

• Mk Vc (type 359) As well as having most of the standard Mk V features this version had several important changes over the earlier Mk Vs, most of them modifications which were first tested on the Mk III:
• The Type C wing "Universal" wing was used.
• The structure was re-stressed and strengthened.
• A deeper radiator fairing was fitted under the starboard wing, and a larger oil cooler, with a deeper, kinked air outlet, to port.
• The Mk Vc introduced the new windscreen design first used on the Mk III. Some Mk Vbs also used this windscreen.
• The elevator horn balances were increased in area.

File:SpitVbtropab1.jpg

Vb Trop of 40(SAAF) Squadron fitted with the "streamlined" version of the Aboukir filter, a Rotol propeller and clipped wings.

With the advent of the superb Focke Wulf Fw 190 in August 1941 the Spitfire was for the first time truly outclassed, hastening the development of the "interim" Mk IX.

The first Spitfires to be sent overseas in large numbers were Mk Vbs. With the advent of the Mk IX in RAF service few of the Mk Vc saw combat over Europe, with the majority of them being used either in North Africa and the Mediterranean or in the Far East.

250 Mk Vcs were shipped to Australia for the RAAF.

Portugal was the recipient of two lots of Spitfire Vbs; 33 refurbished ex-RAF aircraft started arriving in early 1944 and a further and final shipment of 60 mainly clipped wing L.F Mk Vbs arrived in 1947. All were retrofiited with TR 9 HF radios and had no IFF. The last of these Spitfires were taken out of service in 1952.

In total, production was 6,487, consisting of 94 Mk Va, built by Supermarine, 3,911 Mk Vb, (776 by Supermarine, 2,995 Castle Bromwich and 140 Westland) and 2,467 Mk Vc, (478 Supermarine, 1,494 Castle Bromwich, 495 Westland) plus 15 PR Type F by Castle Bromwich.

Mk VI (type 350)

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 Rotol propeller of 10 ft 9 in (3.27 m) diameter. 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 airliner; the pressure differential was only two pounds per square inch. To achieve this the forward and rear cockpit bulkheads were completely enclosed, with all control and electrical cables exiting though special rubber sealing grommets. In addition, the side cockpit door was replaced with alloy skin and the canopy was no longer a sliding unit: externally there were no slide rails. Once the pilot was in, the canopy was locked in place with four toggles and sealed with an inflatable rubber tube. It could be jettisoned by the pilot in an emergency. The windscreen of production Mk VIs was the same as the type fitted to the Mark III and some Mk Vs. The effect was to make 37,000 ft seem like 28,000 ft to the pilot, who would still have to wear an oxygen mask. Pressurisation was achieved by a compressor on the starboard side of the Merlin, fed by a long intake below the starboard exhaust stubs. Mk VIs were built with the Coffman cartridge starter, with a small teardrop fairing just ahead of the compressor intake.

To help smooth out airflow around the wingtips the standard rounded types were replaced by extended, pointed versions extending the wingspan to 40 ft 2 in (12.2 m). Otherwise the wings were Type B.

Despite these efforts, only 100 of the Mk VIs were built by Supermarine. Only two units, 124 Squadron and 616 Squadron, were fully equipped with this version, although several other units used them in small numbers as a stop-gap. The threat of a sustained high altitude campaign by the Luftwaffe did not materialise and, more often than not, the Spitfire VIs were used at lower altitudes where it was outperformed by conventional Spitfires. At high altitudes it was discovered that modified Spitfire Vs could perform almost as well as the Mk VI. At low levels, especially, pilots were often forced to fly with the canopy removed because the cockpit would get uncomfortably hot and they were not confident it would be possible to jettison the canopy in case of an emergency.

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.

Supermarine Spitfire variants part two describes the evolution of the Spitfire with the Two-Stage Merlin engine and the Griffon engine

See also

Related development

• Supermarine S.6B
• Seafire
• Spiteful
• Seafang

See also

• British military history of World War II
• Rolls-Royce Merlin and Griffon
• Supermarine
• Allied technological cooperation during World War II

References

Bibliography

• Bader, Douglas. Fight for the Sky: The Story of the Spitfire and Hurricane. London: Cassell Military Books, 2004. ISBN 0-30435-674-3.
• Dibbs, John and Holmes, Tony. Spitfire: Flying Legend. Southampton UK: Osprey Publishing, 1997. ISBN 1-84176-005-6.
• Jackson, Robert. Spitfire: The History of Britain's Most Famous World War II Fighter. London, UK: Parragon Publishing, 2005. ISBN 0-75258-770-6
• Jane, Fred T. “The Supermarine Spitfire.” Jane’s Fighting Aircraft of World War II. London: Studio, 1946. ISBN 1-85170-493-0.
• Lopes, Eng Mârio Canongia. "Fighters of the Cross of Christ; Fighter Squadrons in the Portugese Air Force, 1940 to 1952". Air Enthusiast Thirteen, 1980. Bromley, Kent, UK
• McKinstry, Leo. Spitfire - Portrait of a Legend. London: John Murray, 2007. ISBN 0-71956-874-9.
• Palfrey, Brett R. and Whitehead, Christopher. Supermarine Spitfire - History of a Legend. Royal Air Force (RAF). [1] Access date: 27 December 2006.
• Quill. Jeffrey. Spitfire: A Test Pilot’s Story. London: Arrow Books, 1983. ISBN 0-09-937020-4.
• Price, Alfred. Spitfire Mark I/II Aces 1939-41. London: Osprey Aerospace, 1996. ISBN 1-85532-627-2.
• Price, Alfred. The Spitfire Story: New edited edition. London: Weidenfeld Military, 1999. ISBN 1-85409-514-5.
• Smallwood, Hugh. Spitfire in Blue. London: Osprey Aerospace, 1996. ISBN 1-85532-615-9
• Spick, Mike. Supermarine Spitfire. New York: Gallery Books, 1990. ISBN 0-8317-14034.

• Spitfire: Frontline Fighter (IWM DVD)
• Spitfire-the pilot's view (DVD)

External links

Wikimedia Commons has media related to:

Supermarine Spitfire

• The Spitfire Site
• The Spitfire Society
• Alan Le Marinel hosts Supermarine Spitfire
• Spitfire Performance Testing
• Spitfire/Seafire Serial Numbers, production contracts and aircraft histories
• Warbird Alley: Spitfire page - Information about Spitfires still flying today
• K5054 - Supermarine Type 300 prototype Spitfire & production aircraft history
• The Spitfire: Seventy Years On - Includes images of the factory
• Spitfire Mk. VIII and Mk. XVI - Temora Aviation Museum page
• National Heritage Warbird Foundation

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Supermarine Spitfire variants part one".