Supermarine Spitfire (early Merlin powered variants)

Infobox Aircraft
name =Spitfire
type =Fighter
manufacturer =Supermarine



caption =Spitfire Vc launching from USS "Wasp"
designer =R. J. Mitchell
first flight =5 March 1936
introduction =1938
retired =1955, RAF
status =
primary user =Royal Air Force
more users =
produced =1938–1948
number built =20,351
unit cost =
variants with their own articles =Seafire Spiteful

The British Supermarine Spitfire was one of the most 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. This article deals with Spitfires powered by early Rolls-Royce Merlin engines which mostly utilised single-speed, single-stage superchargers. The second article describes Spitfire variants powered by later Merlins, with two-stage, two-speed superchargers, and Spitfires powered by Rolls-Royce Griffon engines.

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 20 mm 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 gun bays. 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.

In practice, most aircraft carried the two 20 mm Hispano IIs with 120 rpg and four .303 Browning machine guns 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 litres).

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.

ingle-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. [ [http://mildb.org/app/air/model.php?Keys=Supermarine Type numbers] Retrieved: 10 February 2008.]
*All liquid capacities and measurements are in Imperial units.

Prototype "K5054" (Type 300)

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. The carburettor air intake was shorter and flatter than that of the Mk Is, and was recessed into the centre-section. 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 plan 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. [ [http://www.spitfiresite.com/reference/camouflage-markings/2008/02/k5054-spitfire-prototype.htm Spitfire prototype colours and markings] Retrieved: 11 March 2008.]

After the first few flights "K5054" was returned to the factory, reappearing about 10 days later with an overall pale blue-grey finish (there are still arguments over the actual colour), a high-gloss automotive nitrocellulose-lacquer applied by people from the Rolls-Royce car plant. The tailskid had been replaced by a Dowty manufactured, fully castoring tail-wheel unit. The tailwheel was to be modified several times on the prototype, including using twin tailwheels, each smaller than the single wheel which was standardised. The engine cowlings had been altered slightly and the angled fin tip had become straight topped - the rudder balance was correspondingly reduced in size. Undercarriage fairings had now been fitted to the legs. Although the propeller was still the fixed-pitch, wooden bladed unit the pitch had been changed in an attempt to increase the top speed. Several different types of propeller unit were to be fitted to the prototype. Later in 1936 the wings were replaced with a set which, for the first time, incorporated the famous eight .303 Browning machine-gun armament. Also, some time in late 1936, sets of three special "flame dampening" exhaust stacks were fitted to the exhaust ports. [ [http://www.k5054.com/ K5054 site] Retrieved: 11 March 2008.]

The Spitfire was to fly in this form until 22 March 1937, when a major oil pressure failure led to a "forced-landing" with the undercarriage up. When "K5054" re-emerged from the factory the pale blue finish, which had deteriorated badly, was replaced by the soon to be familiar RAF "Dark Earth"/"Dark Green" camouflage on the top surfaces and a silver finish underneath. This finish was to be worn for the remainder of the airframe's life.

Mk I (type 300)

In 1936, before the first flight of the prototype, the Air Ministry placed an order for 310 Spitfires. Already the biggest problem facing the entire programme was the inability of Supermarine to build the new fighter in the required numbers. In spite of the promises made by the Chairman of Vickers-Armstrongs (the parent company of Supermarine) that the company would be able to deliver Spitfire at a rate of five a week, starting 15 months after the order was placed, it soon became clear that this would not happen. In 1936 the Supermarine company employed 500 people and was already engaged in fulfilling orders for 48 Walrus amphibian reconnaissance aircraft and 17 Stranraer patrol flying boats. In addition the small design staff, which would have to draught the blueprints for the production aircraft, was already working at full stretch. Although it was obvious that most of the work would have to be sub-contracted to outside sources, the Vickers-Armstrongs board was reluctant to allow this to be done. When, finally, other companies were able to start building Spitfire components there were continual delays because either parts provided to them would not fit or the blueprints were inadequate; the sub-contractors themselves faced numerous problems building components which in many cases were more advanced and complicated than anything they had faced before.

As a result of these problems the first production Spitfire "K9788" was not delivered to the RAF until July 1938 with front line service commencing in August 1938. [Price 1999, pp. 61–69.] For a time the future of the Spitfire was in serious doubt, with the Air Ministry suggesting that the programme be abandoned and that Supermarine change over to building the Bristol Beaufighter under licence. The managements of Supermarine and Vickers were able to finally convince the Air Ministry that the problems would be sorted out and, in 1938, an order was placed with the Morris Motor Company for an additional 1,000 Spitfires to be built at new factory at Castle Bromwich. This 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. [Morgan and Shacklady 2000, p. 45.] Over the next three years a large number of modifications were made, most 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).ref label|Note1|a|a

All Merlin I to III series engines relied on external electric power to start; a well known sight on RAF fighter airfields was the "trolley acc" (trolley accumulator) [ [http://www.perth.igs.net/~long/slang.htm RAF slang terms] [http://www.schweboo.com/html/trolley_acculmulator.html Trolley acc] Retrieved: 5 March 2008.] 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 to the side cowling, just beneath the starboard exhausts.

Early on in the Spitfire's life it was found that at altitudes above about 15,000 ft (4,572 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 II, 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, these were replaced by the ground-crew during rearming. Early production aircraft were fitted with a ring and bead gunsight, although provision had been made for a reflector sight to be fitted once one had been selected. In July 1938 the Barr and Stroud GM 2 was selected as the standard RAF reflector gunsight and was fitted to the Spitfire from late 1938. [Morgan and Shacklady 2000, p. 47.]

From the 78th production airframe 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. From the 175th production aircraft, the Merlin Mk III, which had a "universal" propeller shaft able to take a de Havilland or Rotol propeller was fitted. 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. Late in 1940, a Martin-Baker designed quick-release mechanism, allowing the pilot to quickly jettison the cockpit canopy, began to be retroactively fitted to all Spitfires. The system employed unlocking pins, actuated by cables operated by the pilot pulling a small, red rubber ball mounted on the canopy arch. When freed, the canopy was taken away by the slipstream. [Morgan and Shacklady 2000, p. 57.]

Also in early 1939 the manual hand-pump for operating the undercarriage was replaced by a hydraulic system driven by a pump mounted in the engine bay. Before this change was made pilots had the awkward task of having to pump the undercarriage up with their right hand while simultaneously trying to keep the Spitire controlled using the left hand on the control column. This often led to a condition known as "Spitfire knuckle" where pilots skinned their hand on the side of the cockpit while pumping. [Price 1999, p. 70.]

A voltage regulator was fitted in the bay directly behind the pilot. At first this was mounted low in the fuselage. Starting in the N30 series the regulator was repositioned to the rear of the seat bulkhead, appearing low in the rear transparency. From N32, the regulator, which was under a black, cylindrical cover, was secured to the bulkhead directly behind the pilot's headrest. Other changes were made later in 1939 when a simplified design of pitot tube was introduced and the "rod" aerial mast was replaced by a streamlined, tapered design. Also, to improve protection for the pilot and fuel tanks, a thick, laminated glass, bullet proof plate was fitted to the curved, one piece windscreen and a 3 mm thick cover of light alloy was fitted over the top of the two fuel tanks.ref label|Note2|b|b

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. In addition the lower petrol tank was fitted with a fire resistant covering called "Linatex", whach was later replaced with a layer of self-sealing rubber.

In June 1940 de Havilland began manufacturing a kit to convert their two pitch propeller unit to a constant speed propeller. Although this propeller was a great deal heavier than the earlier types (500 lb (227 kg) compared with 350 lb (183 kg)) it provided another substantial improvement in take-off distance and climb rate. Starting on 24 June de Havilland engineers began fitting all Spitfires with these units and by 16 August every Spitfire and Hurricane had been modified. [Morgan and Shacklady 2000, pp. 53–55.] Spitfire Mark I/II Aces] "Two step" rudder pedals were fitted to all frontline Spitfires; 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. Another modification was the small rear view mirror which was added to the top of the windscreen: an early "shrouded" style was later replaced by a simplified, rectangular, adjustable type. 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 which was 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./sq.inch to +12 lbs./sq.inch without damaging the engine. With the +12 lbs./sq.inch "emergency boost", the Merlin III was able to generate 1,160 hp (973 kW) at 9,000 ft in a five minute burst.ref label|Note3|c|c

One of the most important modifications to the Spitfire was to replace the all machine gun armament with wing mounted Hispano 20 mm cannon. In December 1938 Joseph Smith was instructed to prepare a scheme to equip a Spitfire with a single Hispano mounted under each wing. Smith objected to the idea and designed an installation in which the cannon were mounted on their sides within the wing, with only small external blisters on the upper and lower wing surfaces. The first Spitfire equipped with single Hispanos in each wing was "L1007" which was posted to Drem in January 1940 for squadron trials. On 13 January this aircraft, piloted by Plt Off Proudman of 602 Squadron took part in an engagement when a Heinkel He 111 was shot down. Soon after this Supermarine was contracted to convert 30 Spitfires to take the cannon armed wing; 19 Squadron received the first of these in June 1940 and by 16 August 24 cannon armed Spitfires had been delivered. [Morgan and Shacklady 2000, pp. 57–61.]

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).

From November 1940, a decision was taken that Supermarine would start producing light-alloy covered ailerons which would replace the original fabric covered versions. However, seven months after the decision was taken to install them on all marks, Spitfires were still being delivered with the original fabric covered ailerons.Morgan and Shacklady 2000, p. 142.] From this time on, metal ailerons were fitted to all Spitfires coming off the production lines.ref label|Note4|d|d Retrofitting of older Spitfires with the new ailerons proceeded slowly due to the limited capacity of Supermarine, at the rate of 10 sets a week.

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. [Lopes 1990, pp. 19, 20.]

peed 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.ref label|Note5|e|e [ [http://www.fai.org/news_archives/fai/cat_world_records.asp FAI record (current)] Retrieved: 29 April 2008.]

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. [ [http://www.aeroscale.co.uk/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=1500 id=1500 Speed Spitfire] ]

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 Commander 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"ref label|Note6|f|fwere applied and polished. Two two F .24 cameras with five inch (127 mm) 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 PR 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 PR 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. [ [http://ipmsstockholm.org/magazine/2006/05/stuff_eng_profile_pr_spitfires.htm Early PR Spitfire camouflage] Retrieved: 11 February 2008.]

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 (203 mm) 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 convert|20|in|mm|sing=on 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 PR 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. [Smallwood 1996, pp. 40, 41.]

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)

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 engine 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 convert|17000|ft|m, 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.ref label|Note7|g|g

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.The Spitfire Story]

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 (types 331, 349 & 352)

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 convert|20800|ft|m|abbr=on, and could climb to convert|20000|ft|m|abbr=on 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 and VB(trop): The VB became the main production version of the Mark Vs. 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. Starting in early 1941 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. From mid-1941 alloy covered ailerons became a universal fitting.Morgan and Shacklady 2000, p. 142.]

From late 1941 further modifications were made. 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. In addition, a large number of 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 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. [Morgan and Shacklady 2000, p. 148.] A wide bladed Rotol constant speed propeller of 10 ft 10 in (3.29 m) diameter was able to be fitted, resulting in a modest speed increase over 20,000 ft and an increase in the service ceiling. The blades were either "Jablo" (made out of compressed wood) or metal and the spinner was longer and more pointed.

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. In an effort to counter this threat, especially at lower altitudes, the VB 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 and airspeed 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 4720 ft/min (21.6 m/sec) at convert|2000|ft|m|abbr=on [Price 1999, p. 145.]

The Mk VB(trop) (or type 352) 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, but the decreased performance was considered acceptable. This variant was also fitted with a larger oil tank and desert survival gear behind the pilot's seat. A new "desert" camouflage scheme was applied. Many VB(trop)s were modified by 103 MU (Maintenance Unit-RAF depots in which factory fresh aircraft were brought up to service standards before being delivered to squadrons) at Aboukir, 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.ref label|Note8|h|h

*Mk VC and VC(trop) (types 349 and 352/6) 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.ref label|Note9|i|i
* 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.
*More armour plating was added, protecting the bottom of the pilot's seat and the wing ammunition boxes.
* The elevator horn balances were increased in area.

The first Spitfire modified to carry bombs was a VC "EP201" which was modified on Malta to carry one 250 lb bomb under each wing. In a note to the Air Ministry Air Vice Marshal Keith Park wrote:

One VC(trop) "BP985" was modified by 103 MU as a high altitude fighter capable of intercepting the Ju 86P photo reconnaissance aircraft which were overflying Allied naval bases in Egypt. This aircraft was stripped of all unnecessary weight, including all armour plating and the Hispano cannon and the compression ratio of the Merlin 46 was increased by modifying the cylinder block. A four bladed de Havilland propeller was fitted along with an "Aboukir" filter, a larger 9.5 gallon oil tank and extended wingtips. [Morgan and Shacklady, 2000 pp. 155–156.]

The first Spitfires to be sent overseas in large numbers were Mk VBs; many of these were built as VC(trop)s. With the advent of the Mk IX to 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.

A total of 250 Mk VC(trop)s were shipped to Australia for the RAAF; the first of these arrived in late 1942.

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 retrofitted with TR 9 HF radios and had no IFF. The last of these Spitfires were taken out of service in 1952. [Lopes 1980, pp. 21, 22, 24, 25.]

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 VB, (478 Supermarine, 1,494 Castle Bromwich, 495 Westland) plus 15 PR Type F by Castle Bromwich.

Daimler Benz powered Spitfire Vb

In November 1942 a Spitfire Vb "EN830" "NX-X" of 131 Squadron made a "forced landing" in a turnip field at Dielament Manor, Trinity, Jersey. This aircraft was repairable and started being test flown in German markings and colours at the "Luftwaffe" research facilities at Rechlin. There it was proposed that the Spitfire's Merlin engine should be replaced by a Daimler-Benz DB 605A inverted Vee-12 engine; the Spitfire was sent to Echterdingen, south of Stuttgart, where Daimler-Benz operated a flight testing division.

When the Merlin engine was removed it was discovered that the fuselage cross section was virtually identical to that of the engine nacelle of a Messerschmitt Bf110G. Consequently a new engine support structure was built onto the Spitfire's fuselage and the DB 605 engine and cowling panels added. A propeller unit and supercharger air intake from a Bf 109 G completed the installation.

Other changes made were to replace the Spitfire instruments with German types and the electrical system was also changed from the standard 12 volt system to the German 24 volt type. In this form the Daimler-Benz Spitfire started flying in early 1944. The Spitfire was popular with German pilots and was flown regularly until it was destroyed in a USAAF bombing raid on 14 August 1944. [ [http://www.unrealaircraft.com/hybrid/spitfire.php DB powered Spitfire Vb] Retrieved: 4 April 2008.]

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 convert|37000|ft|m|abbr=on seem like convert|28000|ft|m|abbr=on 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 (type 367)

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.

Further|Supermarine Spitfire (late Merlin powered variants) describes the evolution of the Spitfire with the two-stage Merlin engine and the Griffon engine

ee also

Aircontent
related =
* 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

Footnotes

*note label|Note1|a|aProblems with the engine cutting out through carburettor design are described under Rolls-Royce Merlin and Supermarine Spitfire. Early Spitfires were disadvantaged against Bf 109s which, with their direct fuel injection, could push straight into a dive. Spitfire pilots would have to half roll, pull the control column back into a dive (positive -G) then roll back out again, by which time the Bf 109 was usually long gone.
*note label|Note2|b|bThis was capable of deflecting small calibre rounds.
*note label|Note3|c|cIf the pilot resorted to emergency boost, he had to report this on landing and it had to be noted in the engine log book.
*note label|Note4|d|dCombat experience showed fabric covered ailerons seemed to lock solid in high speed dives: this was caused by the fabric "ballooning" which, in turn, increased the control stick forces needed to move them. Supermarine quickly produced a set of ailerons covered with light alloy and, in November 1940, these were fitted to a trial Mk I. Pilots reported a considerable improvement in handling at high speeds. Fighter Command ordered a crash programme to have all front line Mk Is and Mk IIs fitted. However, Spitfires were still being delivered with fabric covered ailerons in June 1941. [Morgan and Shacklady 2000, p.142.] Douglas Bader had the Spitfires of his Wing fitted with the new ailerons after contacting the factory directly. Since his airfield was so close to the factory he arranged for the fighters to fly to the factory airfield and be refitted one at a time.
*note label|Note5|e|eWorld Speed Records and other aviation records were and still are set by the "Fédération Aéronautique Internationale (FAI)". A record needs to be set over a recognised course at a set altitude to be valid. The Speed Spitfire would have came under the category CLASS C, GROUP 1d
*note label|Note6|f|fThe name "Camoutint" was used by the manufacturers of the paint. This blue/green colour was later used by the RAF as the basis of a "Sky (Type S)". It was the first in a new range of smooth, eggshell finish paints replacing the drag inducing matt finishes in use up until 1942. A "Camoutint Pink" was later used on some low-flying PR Spitfires, including the Type E and some Type G and FR IXs.
*note label|Note7|g|g On 9 March 2008, a Spitfire Mk II "P8563", which fatally crashed into a peat bog in 1942, was unearthed by a group of aviation archaeologists [ [http://www.spitfiresite.com/history/articles/2008/03/spitfire-excavation.htm Spitfire excavation] Retrieved: 20 March 2008.]
*note label|Note8|h|hMost VC wings had a large, bulged fairing on top of the wing to provide clearance for the ammunition feed motors of two Hispano cannon in each wing: because two cannon were seldom fitted these fairings were later reduced in size to more streamlined shapes.

Citations

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 Tony Holmes. "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: Parragon Publishing, 2005. ISBN 0-75258-770-6.
* Jane, Fred T., ed. "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 Portuguese 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.
* Morgan, Eric B and Edward Shacklady. "Spitfire: The History." Stamford: Key Books Ltd, 2000. ISBN 0-946219-48-6.
* Palfrey, Brett R. and Christopher Whitehead. [http://www.raf.mod.uk/history/spit1.html "Supermarine Spitfire: History of a Legend".] Royal Air Force (RAF). Retrieved: 27 December 2006.
* Price, Alfred. "Spitfire Mark I/II Aces 1939-41". London: Osprey Aerospace, 1996. ISBN 1-85532-627-2.
* Price, Alfred. "Spitfire Mark V Aces 1941-45". London: Osprey Aerospace, 1997. ISBN 1-85532-635-3.
* 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.
* Quill. Jeffrey. "Spitfire: A Test Pilot’s Story". London: Arrow Books, 1983. ISBN 0-09-937020-4.
* Spick, Mike. "Supermarine Spitfire". New York: Gallery Books, 1990. ISBN 0-8317-14034.
* [http://www.dukevideo.com/General/DVD/Military%20,-a-,%20War/Spitfire%20Frontline%20Fighter%20DVD.aspx Spitfire: Frontline Fighter (IWM DVD)]
* [http://www.dukevideo.com/General/DVD/Aviation/Plane%20Profiles/Spitfire%20-%20the%20Pilot-q-s%20View%20DVD.aspx Spitfire-the pilot's view (DVD)]

External links

* [http://www.spitfiresite.com/ The Spitfire Site]
* [http://www.spitfiresociety.demon.co.uk/ The Spitfire Society]
* [http://www.supermarine-spitfire.co.uk/spitfire.html Alan Le Marinel hosts Supermarine Spitfire]
* [http://www.spitfireperformance.com/spittest.html Spitfire Performance Testing]
* [http://www.spitfires.ukf.net/home.htm Spitfire/Seafire Serial Numbers, production contracts and aircraft histories]
* [http://www.warbirdalley.com/spit.htm Warbird Alley: Spitfire page - Information about Spitfires still flying today]
* [http://www.k5054.com/ K5054 - Supermarine Type 300 prototype Spitfire & production aircraft history]
* [http://www.birmingham.gov.uk/GenerateContent?CONTENT_ITEM_ID=86855&CONTENT_ITEM_TYPE=0&MENU_ID=10468 The Spitfire: Seventy Years On - Includes images of the factory]
* [http://www.aviationmuseum.com.au/aircraft/Spitfire.cfm Spitfire Mk. VIII] and [http://www.aviationmuseum.com.au/aircraft/spitfiremkxvi.cfm Mk. XVI] - Temora Aviation Museum page
* [http://www.warbirdfoundation.org/ National Heritage Warbird Foundation]