Supermarine Spitfire (early Merlin-powered variants)

Supermarine Spitfire

Industry	Aerospace, Military aviation
Founded	1936
Founder	R. J. Mitchell
Headquarters	Southampton , United Kingdom
Products	Fighter aircraft

This article is about Spitfires equipped with early Merlin engines. For variants with later Merlin engines, see Supermarine Spitfire (late Merlin-powered models). For Spitfires fitted with Rolls-Royce Griffon engines, see Supermarine Spitfire (Griffon-powered models).

File:Spitfire F VB BM597.jpg

Spitfire Mk Vb BM597 from Duxford's Historic Aircraft Collection, displayed in the colours of 317 (Polish) "Wileński" Squadron.

Early Rolls-Royce Merlin engine-powered Supermarine Spitfire variants predominantly featured single-stage, single-speed superchargers. The British Supermarine Spitfire stood as the sole Allied fighter aircraft to serve continuously on the front lines throughout the entirety of the World War II, from its outbreak in September 1939 until August 1945. Its operational life extended into the post-war era, remaining active into the 1950s. The fundamental airframe demonstrated remarkable flexibility, accommodating significantly more powerful engines and heavier armaments than initially intended for its original role as a short-range interceptor. This adaptability resulted in the production of 19 distinct marks and 52 sub-variants during and following the war. Modifications were driven by evolving Royal Air Force needs and the necessity to counter increasingly advanced enemy fighters. Following the passing of the original designer, R. J. Mitchell, in June 1937, all subsequent Spitfire designs were developed under the leadership of his successor, Joseph Smith, alongside a dedicated team of engineers and draftsmen.

Wing configurations

Spitfires equipped with single-stage Merlin engines featured five distinct wing configurations: Type A, B, C, D, and E wings. While these shared identical dimensions and outlines, their internal layouts for armament and fuel storage varied. All Mk I, II, and V models along with their variants were fitted with small rectangular undercarriage indicator pins that extended at an angle from the upper wing surfaces when the landing gear was securely lowered. This provided a definitive mechanical confirmation of gear deployment since the pilot lacked direct visual access to the landing gear. These pins served as a fail-safe alongside the instrument panel indicator lights, ensuring warning in case of electrical failure. Across these variants, Dunlop AH2061 tyres were used on five-hole alloy main wheels, while fixed castering tailwheels ran on Dunlop AH2184 tyres.

Beginning with the Mk V series, certain Spitfires featured modified wing tips where the characteristic rounded elliptical ends beyond the ailerons were "clipped" and replaced with shorter squared-off fairings. This adjustment aimed to boost low-altitude agility and improve roll responsiveness—a performance area where the Mk V lagged behind its competitor, the Fw 190. Although these modified aircraft are commonly referred to as "LF" models due to their designation as Spitfire LF Mk V, the "L" actually denotes the variant of Rolls-Royce Merlin engines optimized for low-altitude operation. These engines employed "cropped" supercharger impellers (such as Merlin 45M, 50M, or 55M). While many "LF" Spitfires adopted clipped wings to complement these engine variants, several retained their original elliptical tips.

A type

The A-type wing represented the initial design and was armed with eight .303 calibre Browning machine guns, each supplied with 300 rounds. This wing’s fundamental structure remained consistent until the introduction of the C type in 1942. One significant modification early in production was the installation of a heating system within the gun bays to prevent freezing at high altitudes. To facilitate this, open elements such as wing ribs enclosing the gun bays were sealed off to create enclosed compartments for each weapon. Heated air was channeled from the engine radiator through ducting into these sealed bays. Air was expelled via vents beneath the wings covered by streamlined triangular blisters positioned just inside the wingtips; this created a pressure differential that drew in warm air continuously without needing mechanical assistance. To prevent cold air ingress through the muzzle openings on the leading edge, ground crews applied red fabric adhesive tape during ammunition loading. The guns fired through this tape; however, it was not replaced after combat sorties. Additionally, late in 1940, fabric-covered ailerons were substituted with those made from light alloy. The A-type wing configuration was solely compatible with an armament of eight .303 calibre Browning machine guns.

B type

The B-type wing was essentially an adaptation of the A type, altered to mount a single 20 mm Hispano cannon on each wing, replacing the two inner .303 machine guns. The retractable landing lamp beneath the wing was relocated. The cannon was positioned in the innermost machine gun bay adjacent to the wheel well, while the second inner gun was completely removed. The space previously occupied by the ammunition trays for the inner guns, located outboard of the cannon bay, was transformed into a compartment designed to hold a 60-round drum magazine for the cannon. To accommodate the large ammunition drum, bulges were incorporated into both upper and lower wing skins (with underwing blisters appearing in two distinct shapes). The outer pairs of .303 machine guns remained unchanged. Only one armament configuration could be installed on a Spitfire equipped with B-type wings: two 20 mm Hispano Mk II cannons, each supplied with a 60-round drum, combined with four .303 caliber Browning machine guns in the outer positions, each carrying 350 rounds per gun. Ailerons with alloy coverings became standard equipment on this wing variant.

C type

Known as the "C-type" or "Universal wing," this design was extensively reworked to streamline production and assembly times while enabling various armament setups within a single adaptable wing structure. This universal design permitted multiple weapon configurations without significant structural changes—an approach mirrored in the Hawker Hurricane, which could be outfitted with anything from eight to ten .303 Brownings, four 20mm Hispanos, or twin anti-tank 40mm Vickers "S" guns alongside two .303s. Without alterations, the universal wing could accept "A," "B," "C," or "E-type" armaments, though the "E" type was introduced only in later Spitfire models. Among these configurations, the "B" type layout featuring two cannons and four Brownings was most frequently observed on "C" wing Spitfires until superseded by the Mk IX and its "E" wing. Differences in the "C" wing include an additional cannon bay adjacent to the first and repositioning of the #3 Browning slightly outward from ribs 13 to 14, resulting in the outer machine guns being closer together than on earlier "B" wings.

Officially, any aircraft fitted with a universal wing is classified as a "C" variant regardless of its armament setup (excluding "E" types). However, in later common but inaccurate usage, "C" variants armed identically to "B" types are often referred to as "B" variants despite structural differences from original "B" wings. The redesigned wing featured two inner cannon bays, though typically only one was armed. Additionally, the outer pair of .303 machine guns were spaced closer together compared to those on "A" or "B" wings—this serves as a key visual cue distinguishing genuine "B" wings from later universal-wing-equipped Spitfires with similar armaments. The second cannon bay ports remain visible even when unarmed and are usually sealed with rubber plugs when empty. Cannon mounts were also shifted rearward within the wing, resulting in shorter barrel fairings compared to those on original "B" Spitfires.

Few if any Spitfires with universal wings were produced using the eight .303 Browning "A" armament setup since it was considered outdated by Mk V’s introduction into combat. The C-type wing marked the first instance capable of supporting an all-cannon loadout of four 20mm Hispanos; thus, four-cannon Spitfires (such as Mk Vc) are commonly associated with the "C" designation. Nevertheless, this armament configuration was seldom employed due to added weight impairing performance and maneuverability; many Spitfires initially equipped with this setup had extra cannons removed in operational conditions to reduce weight. Although theoretically possible for a universal-wing Spitfire to carry four 20mm cannons plus four .303 Brownings simultaneously, this heavily burdened arrangement was never utilized. (The later-developed "E" type wing—found on Mk IX and subsequent models—offered a similar layout but replaced the inner pair of Hispanos with two American .50 caliber Browning AN/M2 heavy machine guns, yielding an armament of two Hispanos and two .50 caliber Brownings.)

The Universal wing also reflected modifications made when Hispano cannons were converted to belt-feed, doubling their ammunition capacity to 120 rounds per gun housed in trays rather than 60 rounds in drums as seen on Mk Vb’s original drum-fed cannons. This advancement eliminated the need for large under- and over-wing blisters that accommodated bulky ammunition drums, requiring only a small blister for covering the electrical "Chattellerault" feed mechanism. The undercarriage mountings underwent redesigns as well; undercarriage doors were given a bowed cross-section allowing landing gear legs to sit lower within their wells, removing upper-wing blisters over wheel wells and pivot points.

Strengthened undercarriage legs were angled forward by approximately 2 inches (5.08 cm) when extended, enhancing ground stability and reducing nose-over incidents during taxiing or landing. Furthermore, retractable landing lights were omitted. Structural hardpoints were added outside wheel wells to enable attachment of racks beneath each wing capable of carrying one 250 lb (113 kg) bomb apiece.

D type

The D type variant was adapted specifically for unarmed, extended-range photo-reconnaissance Spitfires, such as the PR Mk Id (with PR models detailed further below). In these versions, weapon compartments were left empty, and the leading edge wing section ahead of the main spar—characterized by its relatively thick skin—was transformed into integral auxiliary fuel tanks. These tanks could hold an additional 66+1⁄2 Imperial gallons (300 L) on top of the fuel stored in the fuselage tanks located forward of the cockpit. The filler caps were positioned well outboard, between ribs 19 and 20 on the leading edge, due to the wing tips being elevated relative to the rest of the wing because of dihedral, making this the only feasible location for a fuel filler cap. To prevent tank rupture from vapor expansion caused by solar heating on the thin metal wing skin—which also served as tank walls—an expansion and overflow vent was installed. This vent was situated further outboard, between ribs 20 and 21, at the highest point within the tank where vapor naturally accumulates.

Mark numbers, type numbers

Mark numbers did not always follow a strict chronological sequence; for instance, the Mk IX was introduced as an interim solution prior to production of Mks VII and VIII. Additionally, aircraft originally built as one mark or variant were sometimes converted to another—for example, several early Mk Vbs were modified from Mk Ibs; similarly, initial Mk IXs originated as Mk Vcs and were converted in certain cases by Rolls-Royce at their Hucknall facility.

Up to late 1942, the RAF consistently employed Roman numerals for mark designations. Between 1943 and 1948, a transitional phase occurred during which new aircraft entering service received Arabic numerals while older models retained Roman numerals. From 1948 onward, Arabic numerals became standard exclusively. This article follows the convention of using Roman numerals for Mks I through XVI and Arabic numerals for Mks 17 to 24. Type numbers (such as Type 361) refer to Supermarine's internal design drawing numbers.

Prototype K5054 (Supermarine Type 300)

Main article: Supermarine Spitfire prototype K5054

Construction on K5054 commenced in December 1934 and incorporated various modifications during its build. A significant alteration involved the Merlin engine’s cooling system, which adopted ethylene glycol coolant combined with a ducted radiator inspired by Frederick Meredith’s research at the Royal Aircraft Establishment, Farnborough.

Its maiden flight occurred on 5 March 1936. The aircraft was initially unpainted with fixed undercarriage lacking fairings and carried no armament. The powerplant was a prototype Merlin C engine delivering 990 hp (738 kW).

Following several initial flights, K5054 returned to the factory and reemerged approximately ten days later featuring an overall glossy pale blue-grey paint scheme. Engine cowlings were modified; the fin tip changed from angled to straight-topped with a corresponding reduction in rudder balance size. Undercarriage legs were fitted with fairings, and an improved propeller was installed. With performance now meeting expectations, it was handed over to the RAF for service evaluation.

Later in that year, standard armament comprising eight .303" Browning machine guns was installed. On 22 March 1937 K5054 made a forced landing with its undercarriage retracted. During repairs it received a standard Dark Earth/Dark Green camouflage pattern on top surfaces and silver dope underneath. On 19 September 1938 it flew for the first time equipped with ejector exhausts that provided an additional thrust of seventy pounds.

The aircraft’s operational career concluded on 4 September 1939 during testing at Farnborough, when a miscalculated landing caused it to overturn onto its back, resulting in fatal injuries to pilot Flt Lt. White and total loss of the airframe.

Mk I (Type 300)

File:Commons-logo.svg Media related to at Wikimedia Commons

File:SpitI19a.jpg

K9795, the ninth production Mk I, serving with 19 Squadron, features the wooden two-blade fixed-pitch propeller, the early "unblown" canopy, and the "wraparound" windscreen lacking bulletproof glass. The original style aerial mast is also present.

In 1936, prior to the prototype's maiden flight, the Air Ministry placed an order for 310 Spitfires. Despite assurances from the Chairman of Vickers-Armstrongs—Supermarine’s parent company—that production could reach five aircraft per week, it quickly became apparent this target was unattainable. At that time, Supermarine employed around 500 workers and was already committed to manufacturing 48 Walrus amphibian reconnaissance planes and 17 Stranraer patrol flying boats. The limited design team responsible for creating production blueprints was operating at full capacity. Although subcontracting much of the work was inevitable, Vickers-Armstrongs’ board hesitated to approve outsourcing. When other firms began fabricating Spitfire components, persistent delays occurred due to ill-fitting parts or incomplete blueprints; subcontractors faced numerous challenges producing components that were often more complex and advanced than anything previously attempted.

As a result of these setbacks, the RAF received its first two production Spitfires only in July 1938, with 19 Squadron becoming the first unit to receive a Spitfire in early August. At one point, the continuation of the Spitfire program was uncertain, with the Air Ministry proposing cancellation and suggesting Supermarine switch to licensed production of the Bristol Beaufighter. Eventually, Supermarine and Vickers management persuaded the Air Ministry that production issues could be resolved. Consequently, in 1938 an order for an additional 1,000 Spitfires was placed with Morris Motors Limited to be manufactured at a new large facility planned for Castle Bromwich. This was supplemented in 1939 by orders for 200 more from Woolston, followed just months later by another 450 units. These combined orders totaled 2,160 aircraft—among the largest in RAF history. Over the subsequent three years, numerous modifications were implemented based largely on combat experience.

Early operational use revealed a significant issue: above approximately 15,000 ft (4,572 m), condensation could freeze inside the guns. To address this problem, a gun heating system initially fitted to K5054 was introduced on the 61st production Mk I. At World War II’s outbreak, flash-hiders were removed from gun muzzles and fabric patches were used to seal gun ports; these patches kept barrels clean and enhanced heating efficiency. Initial production models featured a ring and bead gunsight, though provision existed for installing a reflector sight once selected. In July 1938, the Barr and Stroud GM 2 reflector gunsight was chosen as standard RAF equipment and fitted from late that year onward. These early Mk Is achieved a top speed of 362 mph (583 km/h) at 18,500 ft (5,600 m), with a peak climb rate of 2,490 ft/min at 10,000 ft (3,000 m) and a service ceiling (defined as climb rate dropping to 100 ft/min) of 31,900 ft (9,700 m).

All Merlin I through III engines required external electric power for starting; a common sight at RAF fighter bases was the "trolley acc"—a mobile battery unit wheeled up to aircraft. The power lead connected into a small recess on the starboard side cowling of the Spitfire. On Supermarine-built models, a small brass instruction plate was affixed beneath the starboard exhausts.

Initial Mk Is were equipped with the 1,030 hp (768 kW) Merlin Mk II engine paired with an Aero-Products "Watts" two-blade wooden fixed-pitch propeller measuring 10 ft 8 in (3.3 m) in diameter and weighing 83 lb (38 kg). From the 78th airframe onward, this was replaced by a heavier (350 lb/183 kg) three-bladed metal de Havilland propeller measuring 9 ft 8 in (2.97 m), featuring two pitch positions that significantly enhanced takeoff performance, top speed, and service ceiling. The Merlin Mk III engine with a "universal" propeller shaft compatible with de Havilland or Rotol propellers was introduced starting from the 175th aircraft produced. In response to pilot feedback, an improved "blown" canopy began replacing the original flat version in early 1939; it offered increased headroom and better lateral and rear visibility.

Simultaneously, manual hand-pumps used for undercarriage operation were replaced with hydraulic systems powered by an engine bay-mounted pump. Spitfire Is incorporating these upgrades attained a maximum speed of 367 mph (591 km/h) at 18,600 ft (5,700 m), climbed at up to 2,150 ft/min at 10,000 ft (3,000 m), and had a service ceiling of 34,400 ft (10,500 m).

A voltage regulator housed under a black cylindrical cover was installed low on frame 11 behind the pilot’s seat: beginning with N30xx series aircraft it was relocated higher within the rear transparency area; from N32xx onwards it sat directly behind the pilot's headrest on frame 11. Additional changes introduced in late 1939 included fitting a simplified pitot tube design and replacing the "rod" aerial mast with a streamlined tapered version. To enhance protection for pilot and fuel tanks, thick laminated bulletproof glass plates were installed on curved one-piece windscreens along with a light-alloy cover approximately three millimeters thick over both fuel tanks capable of deflecting small-caliber rounds. Around mid-1940, about seventy-three pounds (33 kg) of armored steel plating was added as head and back protection on seat bulkheads and shielding over glycol header tanks. Furthermore, lower petrol tanks received fire-resistant "Linatex" coverings later succeeded by self-sealing rubber layers.

In June 1940 de Havilland began producing kits converting two-pitch propellers into constant speed propeller units. Although substantially heavier (500 lb/227 kg versus previous 350 lb/183 kg), these offered marked improvements in takeoff distance and climb rate. Starting on June 24th engineers commenced retrofitting all Spitfires with these propellers; by August 16th every Spitfire and Hawker Hurricane had been upgraded accordingly. Frontline Spitfires received "two step" rudder pedals permitting pilots to raise feet higher during combat maneuvers—enhancing blackout thresholds under high G-forces and enabling tighter sustained turns. Another addition was a small rearview mirror mounted atop windshields—initially an enclosed design later replaced by simpler rectangular adjustable types.

File:Spitfire1602a.jpg

A Spitfire Mk Ia from 602 Squadron circa early 1940 displaying a de Havilland three-blade propeller alongside "blown" canopy, laminated bulletproof windscreen, and updated aerial mast. The brass plate below starter plug is visible on engine cowling.

Beginning September 1940, Identification Friend or Foe (IFF) equipment weighing approximately forty pounds (18 kg) was installed featuring wire aerials stretched between tailplane tips and rear fuselage. Although this added weight and drag reduced maximum speed by about two mph (three km/h), it enabled radar identification as friendly units—a deficiency contributing to incidents like the Battle of Barking Creek. Around this time new Very High Frequency (VHF) T/R Type 1133 radios started replacing older High Frequency (HF) TR9 sets—initially fitted in May to Spitfires in No. 54 Squadron RAF and No. 66 Squadron RAF, but widespread installation delayed by production issues until roughly five months later. Pilots benefited from clearer communications aiding coordination within Wing formations adopted across RAF Fighter Command by 1941. This upgrade eliminated wires between aerial mast and rudder as well as removing triangular prongs atop masts.

Later-production Spitfire Is experienced reduced maximum speeds due to increased weight and aerodynamic changes but gained superior takeoff distances and climb rates thanks to constant-speed propellers. During the Battle of Britain, these aircraft attained speeds up to 353 mph (568 km/h) at 20,000 ft (6,100 m), climbing at rates reaching 2,895 ft/min at 10,000 feet (3,000 m).

Although running on standard-grade (87 octane) fuel with Merlin II engines delivering around 1,030 hp (768 kW) at +6.6 lbs boost pressure by early 1937 Air Ministry officials recognized benefits of higher octane fuel enabling increased boost pressures especially at lower altitudes—and committed to adopting standardized use of 100 octane fuel across RAF units. By late 1937 contracts sourced supplies from United States and Trinidad refineries but concerns over US neutrality prompted diversification so that by April 1940 deliveries arrived from seven sources including British, Dutch West Indies refineries plus US Shell suppliers. This allowed pilots access to emergency boost settings up to +12 psi for five-minute intervals yielding output near 1,310 hp (977 kW) at 3,000 rpm around 9,000 feet altitude. This enhancement raised maximum speeds by about 25 mph at sea level and 34 mph at 10,000 feet while improving climb performance between ground level and full-throttle altitude limits. Engine damage risks remained minimal if emergency boost protocols outlined in pilot manuals were observed—including mandatory reporting after use via breaking wire 'gates' installed as indicators replaced during ground servicing. Similar boost capabilities applied to Merlin XII engines powering Spitfire II variants.

Late in 1940 Martin-Baker developed quick-release canopy mechanisms retrofitted across all Spitfires allowing pilots to jettison canopies swiftly by pulling red rubber ball cables mounted on canopy arches—the slipstream then carried canopies clear. One critical armament upgrade involved replacing machine guns with wing-mounted Hispano-Suiza HS.404 cannon units. In December 1938 Joseph Smith designed arrangements mounting single Hispano cannons within each wing oriented sideways beneath minimal external blisters covering drum magazines holding sixty rounds each—contrasting earlier proposals for underwing mounts which Smith opposed due to aerodynamic concerns.

The first Hispano-armed Spitfire L1007 underwent squadron trials at Drem January 1940 where it participated in combat resulting in downing a Heinkel He 111. Subsequently Supermarine received contracts converting thirty aircraft with cannon-equipped wings; deliveries commenced June 1940 with No. 19 Squadron RAF receiving initial units followed by twenty-four cannon-armed fighters delivered by mid-August. These variants were designated Mk Ib whereas earlier eight-Browning machine gun configurations became known retrospectively as Mk Ia. Early cannon installations suffered frequent jamming—with one engagement seeing only two out of twelve aircraft able to expend all ammunition successfully—prompting further mount improvements for subsequent deliveries such as those issued to No 92 Squadron before settling on mixed armament layouts combining two cannons with four machine guns typical for initial Mk Vb models.

File:Aircraft of the Royal Air Force, 1939-1945- Supermarine Spitfire. CH1451.jpg

X4474, a late-production Mk I flown by Sergeant Jennings of No 19 Squadron during September 1940 showing absence of triangular prong atop mast indicating VHF radio installation along with visible voltage regulator beneath rear transparency—providing contrast against earlier K9795.

From November 1940 plans were made for Supermarine to transition production from fabric-covered ailerons to light-alloy covered versions—a change driven by combat experience revealing fabric surfaces tended to balloon during high-speed dives causing control lock-ups that increased stick forces dramatically. Trial fittings began November 1940 showing notable handling improvements leading RAF Fighter Command to order rapid retrofit programs across frontline Mk I and Mk II fleets—but despite directives many aircraft continued leaving factories equipped with fabric-covered control surfaces as late as mid-1941.

Foreign Orders: Mk Is

The designations 332, 335, 336, and 341 were assigned to Mk I variants intended for customization according to the specifications of Estonia, Greece, Portugal, and Turkey respectively. Estonia's procurement was terminated following the Soviet annexation of the nation. The Foreign Office declined the requests from Greece and Portugal. Although authorization was granted for 59 aircraft destined for Turkey, only two were delivered before the Foreign Office imposed a suspension in May 1940. Additionally, the 208th Spitfire I produced was sold to France and delivered in June 1939 for assessment.

In 1941, the British government consented to provide Portugal with 18 Spitfire Mk 1as. These units were refurbished from RAF reserves, equipped with TR 9 HF radios but lacking IFF systems. Arriving from late 1942, they were assigned serial numbers 370 through 387 and formed the XZ Esquadrilha based at Tancos. All were dismantled by the close of 1947.

Speed Spitfire (Type 323)

Main article: Supermarine Speed Spitfire

In 1937, proposals emerged to adapt a Spitfire for an attempt at the world landplane speed record. At that time, the record stood at 352 mph (566 km/h), held by Howard Hughes piloting a Hughes H-1 racing plane. While an early Spitfire I could reach speeds of 362 mph (583 km/h) at full throttle at approximately 16,800 ft (5,100 m), the official record required flying a 1.86-mile (2.99 km) course no higher than 245 ft (75 m). The sole flying prototype Spitfire could manage 290 mph (470 km/h) at low altitude. On November 11, 1937, Herman Wurster flew a modified Messerschmitt Bf 109 V13 (D-IPKY) to raise the world speed record to 379 mph (610 km/h). Despite this, it was believed that a modified Spitfire might surpass this mark, prompting the Air Ministry to commission funding for such development.

Consequently, a standard Mk I K9834—the 48th Spitfire produced—was withdrawn from production and altered for the speed record challenge. All military hardware was stripped out; hinged gun panels, radio door, and flare chute openings were replaced with removable covers. A specialized "sprint" Merlin II engine running on a unique "racing fuel" blend of petrol, benzol, methanol, and small quantities of tetraethyl lead generated up to 2,100 hp (1,565 kW) for brief intervals. This powered a Watts coarse pitch four-bladed wooden propeller measuring 10 ft (3.0 m) in diameter. Engine cooling was managed via a pressurized water system requiring a deeper radiator housed within an extended duct reaching the trailing edge of the starboard wing. Additionally, an enlarged oil cooler was installed beneath the port wing. The wingspan was shortened to 33 ft 9 in (10.28 m) with rounded wingtips.

Panel seams were filled and smoothed; round-headed rivets on wing surfaces were replaced with flush rivets; an elongated "racing" windscreen was fitted; and a tailskid took the place of the tailwheel. The aircraft's exterior featured a highly polished gloss Royal Blue and Silver paint scheme. Ultimately, this modified Spitfire weighed approximately 298 lb (135 kg) more than a standard late-1930s model. Meanwhile, in June 1938, the Heinkel He 100 V2 established a new speed record of 394.6 mph (635.0 km/h), nearing the anticipated top speed of the Speed Spitfire prior to its maiden flight on November 11, 1938; by late February 1939 it had achieved 408 mph (657 km/h) at around 3,000 ft (910 m).

Further enhancements were deemed necessary. The radiator was removed and replaced by a "total loss" cooling system; the upper fuel tank gave way to an integrated condenser and water tank assembly. Water circulated through the engine before returning to the tank where condensation occurred; excess water was expelled as steam jets from beneath the engine. Calculations indicated that this system would allow completion of speed runs and safe landing before depletion of water and reduced fuel supplies.

Following rapid successive world speed records set by the Heinkel He 100 V8 (463.9 mph (746.6 km/h) on March 30, 1939) and Messerschmitt Me 209 V1 (469.22 mph (755.14 km/h) on April 26, 1939), it became evident that extensive modifications would be required for the Speed Spitfire to compete effectively; consequently, development ceased.

At war’s outbreak, the Speed Spitfire underwent conversion into a hybrid PR Mk II configuration: its specialized Merlin II engine was swapped for a Merlin XII coupled with a variable-pitch de Havilland propeller; additionally, the racing windscreen was replaced by a PR wrap-around type. Due to limited fuel capacity it remained unsuitable for operational deployment but served as a liaison aircraft between British airfields during wartime operations until being scrapped in June 1946.Template:Fix/category

Early photo reconnaissance (PR) models

Prior to the outbreak of the Second World War, the prevailing approach for airborne photographic reconnaissance involved adapting existing bomber aircraft. These bombers retained their defensive weaponry, which was essential due to their inability to evade enemy interceptors. However, it quickly became apparent that modified Blenheims and Lysanders were vulnerable to German fighter attacks, resulting in significant losses during missions over enemy territory.

In August 1939, Flying Officer Maurice Longbottom, influenced by Sidney Cotton, submitted a memorandum titled Photographic Reconnaissance of Enemy Territory in War to RAF Headquarters. He argued that fast, compact aircraft with high operational ceilings would be better suited for reconnaissance tasks, relying on speed and altitude to avoid detection and interception. Longbottom suggested modifying Spitfires by removing armaments and radios to accommodate additional fuel tanks and cameras. Following discussions with Air Chief Marshal Hugh Dowding, Air Officer Commanding RAF Fighter Command, two Spitfires—N3069 and N3071—were released by RAF Fighter Command and assigned to the secretive "Heston Flight," led by Acting Wing Commander Cotton.

These Spitfires underwent "Cottonisation," involving the removal of weapons and radio transmitters. The empty gun ports and panel joints were sealed, and the airframes were meticulously smoothed to eliminate imperfections. They were then coated with a distinctive pale blue-green paint known as Camoutint, which was polished to a smooth finish. Two F24 cameras fitted with five-inch (127 mm) focal length lenses were installed in the wing bays vacated by the inboard guns and ammunition boxes as an interim solution. To prevent camera freezing and lens frosting at high altitudes, heating systems were incorporated in all PR Spitfires. These aircraft, later designated as Spitfire Mk I PR Type A, could reach speeds up to 390 mph. Several subsequent sub-variants were conversions of existing fighter airframes performed by the Heston Aircraft Company. The Type D marked the first specialized ultra-long-range model requiring modifications directly from Supermarine.

The Mk I PR Type B (also referred to as Medium Range or MR) featured upgraded F24 cameras with eight-inch (203 mm) focal length lenses, producing images roughly one-third larger than previous versions. A supplementary 29-gallon (132 L) fuel tank was added behind the cockpit fuselage section. Initially, larger cameras were planned for installation immediately aft of the pilot; however, RAF engineers doubted this would maintain proper balance. Cotton demonstrated that removing lead ballast weights from the extreme rear fuselage—which had been installed to counterbalance constant speed propellers—allowed fitting cameras with longer focal lengths without compromising center of gravity. The Type B eliminated the heavy bulletproof windscreen and many early PR Spitfires of this type were equipped with Merlin XII engines paired with Rotol constant-speed propellers featuring the blunt spinner typical of Mk II Spitfires.

The Mk I PR Type C carried a total fuel capacity of 144 gallons (655 L) and was notable as the first photo reconnaissance aircraft capable of reaching targets as distant as Kiel. Additional fuel was stored both behind the pilot and within a 30-gallon (136 L) blister tank mounted under the port wing; this was balanced by a camera fairing beneath the starboard wing. A larger oil tank necessitated reshaping the nose into what became known as the distinctive PR Spitfire "chin." This variant was also called the Long Range or LR Spitfire.

The Mk I PR Type D—sometimes termed Extra Super Long Range Spitfire—was unique as it was not a conversion but rather a purpose-built PR model. Nicknamed "the bowser" due to its substantial fuel load, this version utilized modified D-shaped leading edges on its wings to house integral tanks; starting in early 1940, ribs four through twenty-one were sealed off to create space for approximately 57 gallons (259 L) of fuel per wing. Due to lower priority amid urgent fighter demands, only two hand-built prototypes emerged by October; these also included a rear fuselage tank holding 29 gallons (132 L). An additional 14-gallon (63 L) oil tank was placed in the port wing. Camera installations consisted of two vertically mounted F24s equipped with either eight-inch (20.3 cm) or twenty-inch (50.8 cm) lenses or two vertically mounted F8s fitted with twenty-inch lenses in the rear fuselage compartment. With full fuel loads, the center of gravity shifted rearward significantly, making flight challenging until rear tanks were depleted. Despite these handling difficulties, this type quickly demonstrated its value by capturing images of far-reaching locations such as Stettin, Marseille, Trondheim, and Toulon.

Following successful trials with prototypes P9551 and P9552, production versions—soon renamed PR Mk IV—were adjusted to increase leading edge tank capacity to 66.5 gallons (302 L), eliminating the rear fuselage tank for improved balance. These aircraft featured more powerful Merlin 45 engines used on Mk V models along with heated cockpits enhancing pilot comfort during extended missions. In total, 229 Type Ds were manufactured.

A single example of Mk I PR Type E, serial N3117, was developed specifically for oblique close-up photography rather than high-altitude vertical shots. This model carried an F24 camera within streamlined pods under each wing; these cameras pointed forward but angled slightly outward and downward at approximately fifteen degrees below horizontal. A rear fuselage fuel tank holding 29 gallons (132 L) was also installed. The versatility of N3117 allowed effective target imaging under weather conditions unsuitable for high-altitude photography and informed subsequent development of the Type G.

The Mk I PR Type F served as an interim "super-long-range" variant entering service in July 1940 while awaiting Type D availability. It carried thirty-gallon fuel tanks beneath each wing plus a further twenty-nine gallons in a rear fuselage tank; an enlarged oil tank was also fitted beneath the nose section. This upgrade proved sufficiently effective that most existing Type B and C aircraft were eventually converted to meet Type F standards. Operating from bases in East Anglia, it could just reach Berlin for photographic missions before returning safely home. Fifteen examples utilized Mk V airframes.

The Mk I PR Type G represented the first fighter-reconnaissance variant performing low-level tactical operations similar to those of Type E models. It was equipped with one oblique F24 camera featuring either an eight-inch or fourteen-inch lens positioned on the port side between fuselage frames thirteen and fourteen; two additional vertical F24 cameras were installed within the fuselage—one forward below the oblique camera capable of using five- or eight-inch lenses, and another aft fitted with either eight- or fourteen-inch lenses. A twenty-nine gallon (132 L) fuel tank was located just aft of the cockpit area. Initial PR G conversions used Mk I airframes fitted with Merlin II engines replaced by Merlin 45s; later conversions employed Mk V airframes. Unlike earlier unarmed versions, Type G retained full armament consisting of eight .303 caliber Browning machine guns along with armored windscreens and gunsights.

A hallmark feature among most PR Spitfires was their specially designed "Blown" canopies incorporating large teardrop-shaped side blisters that significantly enhanced pilot visibility rearward and downward—critical for accurate camera operation during missions. The lateral cameras were aligned by matching a small "+" mark on each blister’s side with a fine black line painted on the port outer aileron surface. In all unarmed PR conversions, traditional gunsights were replaced by compact camera control panels allowing pilots to activate cameras remotely, set exposure intervals, and select photo counts.

In 1941, a distinct marking system for PR variants was introduced independent from fighter mark numbers; several earlier conversions were subsequently reclassified:

• The former Type C became known as PR Mk III.
• The former Type D was redesignated as PR Mk IV.
• The former Type E took on the title PR Mk V.
• The former Type F became PR Mk VI.
• The former Type G was renamed PR Mk VII.

Altogether, production totaled 1,567 Mk I airframes: Supermarine manufactured 1,517 between May 1938 and March 1941 while Westland produced an additional fifty from July through September 1941.

Mk II (Type 329)

File:Commons-logo.svg Media related to at Wikimedia Commons

File:Spitfire IIA P7666.jpg

Spitfire Mk IIa P7666 from 41 Squadron. Squadron Leader Donald Finlay piloted P7666 "Observer Corps" and achieved two Bf 109 kills in November 1940.

During the summer of 1939, an early Mk I aircraft, K9788, was equipped with the Merlin XII engine variant for testing purposes. Following the successful trials, it was decided that this version of the Merlin would power the Mk II, which was designated as the first model to be manufactured solely at the extensive new Lord Nuffield shadow factory located at Castle Bromwich.

The primary modification involved the installation of the enhanced 1,175 horsepower (876 kW) Merlin XII engine. Unlike earlier and some subsequent Merlin engines that used an electric starter, this model employed a Coffman engine starter, necessitating a small "teardrop" shaped bulge on the forward starboard cowling. Cooling for the Merlin XII was achieved through a 70% water and 30% glycol mixture, differing from the pure glycol coolant used in previous Merlin versions.

In early 1940, Spitfire Is from 54 and 66 Squadrons were fitted with wide-bladed propellers produced by Rotol, measuring 10 ft 9 in (3.27 m) in diameter. These propellers were distinguished by a larger, more rounded spinner. It was decided that this propeller type would be exclusively adopted for the Mk II. The combination of this engine and propeller boosted top speed by approximately 6–7 mph below 17,000 feet (5,200 m) compared to late Mk Is and also enhanced climb performance. Although added weight resulted in maximum speed figures lower than those of early Mk Is, overall combat effectiveness was significantly improved. The Mk II came in two main variants: the IIa with eight machine guns and the IIb armed with cannons. Production proceeded rapidly, swiftly replacing all remaining Mk Is in active service; those older models were reassigned to Operational Training Units. By April 1941, the RAF had fully transitioned to this updated version. Later on, de Havilland constant-speed propeller units similar to those on Mk Is supplemented the Rotol units.

In early 1941, a limited number of Mk IIs were modified into "Long Range" Spitfires, identifiable by a fixed 40-gallon (182 L) fuel tank mounted beneath the port wing. Carrying full fuel reduced maneuverability and decreased maximum speed by 26 mph (42 km/h), along with diminished climb rate and service ceiling. Several squadrons employed this variant for extended-range bomber escort missions. After withdrawal from frontline duties, fifty Mk IIs were converted for air-sea rescue roles initially designated as Mk IIc (type 375) before being renamed ASR Mk II. These conversions replaced the Merlin XII with the Mark XX engine; additionally, a "rescue pack" was installed in the flare chute and smoke marker bombs were carried under the port wing.

A total of 921 Mk IIs were manufactured exclusively at Castle Bromwich. Some Mk IIs underwent conversion to Mk V standards.

Mk III (Type 330)

The Mk III represented the initial effort to enhance the original Spitfire design, incorporating multiple innovations that influenced subsequent variants. It was equipped with a Rolls-Royce RM 2SM engine, later designated as the Merlin XX, which produced 1,390 hp (1,036 kW) thanks to its two-speed supercharger. The wingspan was shortened to 30 ft 6 in (9.3 m), and the wing area was decreased to 220 square feet (20.4 sq m), while the overall length extended to 30 ft 4 in (9.2 m). The main landing gear was reinforced and angled forward by two inches to improve stability on the ground, featuring flaps that fully enclosed the wheels when retracted. Additionally, the tailwheel became fully retractable. The windscreen underwent a redesign, incorporating an internal laminated glass bulletproof panel and optically flat laminated quarter panels.

The first Mk III, identified as N3297, took to the air on 16 March 1940. Early in 1941, a Spitfire Mk V, W3237, was converted into a Mk III model; however, it lacked the retractable tailwheel feature. Following this modification, W3237 replaced N3297 when the latter was transferred to Rolls-Royce. Subsequently, W3237 served as a test aircraft and remained operational until at least September 1944. Although designed to supersede earlier versions in production, the allocation of limited Merlin XX engines to the Hurricane II series caused the Mk III project to be discontinued. Focus then shifted primarily toward the Mk V series. The Mk III powered by the Merlin XX could reach a top speed of 400 mph (640 km/h) at an altitude of 21,000 ft (6,400 m). The N3297 airframe was repurposed for engine development; its wings were replaced with standard Type A units before delivery to Rolls-Royce at Hucknall. Later, it was fitted with a prototype Merlin 60 two-stage engine and redesignated as type 348, serving as a prototype for the Mk IX.

Mk V (Types 331, 349 and 352)

File:Spitty with clipped wings.jpg

Spitfire LF Mk Vb, BL479, piloted by Group Captain M.W.S Robinson, station commander at RAF Northolt, August 1943. This aircraft features wide-bladed Rotol propellers, an internally armoured windscreen, and "clipped" wings.

By late 1940, the RAF anticipated that the introduction of pressurised Junkers Ju 86P bombers over Britain signaled a forthcoming sustained high-altitude bombing campaign by the Luftwaffe. In response, development commenced on a pressurised Spitfire variant powered by an updated Merlin engine (Mk VI). Since this advanced fighter required time for development, an immediate interim solution was necessary: this resulted in the Mk V.

Fundamentally, the Mk V was based on the Mk I airframe but equipped with the Merlin 45 series engine delivering 1,440 hp (1,074 kW) at take-off. This engine featured a new single-speed single-stage supercharger design. Enhancements to the carburettor enabled fuel flow stability during zero-gravity maneuvers. Numerous Mk I and Mk II airframes were upgraded to Mk V specifications by Supermarine and began entering service with fighter squadrons from early 1941 onward. Most production of the Mk V took place at Castle Bromwich.

Three primary versions of the Mk V were manufactured, each comprising various sub-models:

Mk Va (Type 331)

The Va model retained the Type A wing configuration, armed with eight .303" Browning machine guns. It achieved a maximum velocity of 375 mph (603 km/h) at an altitude of 20,800 ft (6,340 m) and could ascend to 20,000 ft (6,096 m) within 7.1 minutes. Production totaled 94 units. Among the notable Va aircraft was W3185 D-B, piloted by Douglas Bader while leading the Tangmere Wing in 1941. During a "Circus" operation—fighter escorts accompanying a small bomber formation—over Northern France on 9 August 1941, Bader was downed in this plane, possibly due to friendly fire, and subsequently remained a prisoner of war for the remainder of the conflict. In April 1941, two Spitfire Vas, designated R7347 and W3119, were dispatched to Wright Field, Dayton, Ohio, USA, serving as representative samples. Both aircraft underwent evaluation by NACA, including tests involving the installation of specialized NACA "jet-propulsion" exhaust stacks.

Mk Vb and Vb (trop) (Types 349 and 352)

The Mk Vb emerged as the predominant production variant within the Mark V series. Standard equipment included the B wing paired with the Merlin 45 engine series. As manufacturing continued, various alterations were introduced, many of which became standard features on subsequent Spitfire models. Initial production involved converting several Mk Ibs into Mk Vbs at Supermarine. Beginning early in 1941, the original round-section exhaust stacks were replaced by fishtail-shaped versions, providing a slight boost to exhaust thrust. Late-production Vbs and Vcs occasionally featured six shorter exhaust stacks per side—similar to those found on Spitfire IXs and Seafire IIIs—a modification initially specified for Vb(trop) variants. Early issues with undersized oil coolers from the Mk I were resolved by installing larger oil coolers beneath the port wing; these were recognizable by their deeper housings with circular intakes. From mid-1941 onward, alloy-covered ailerons became standard fittings.

File:Spitfire VCs 417 Sqn RCAF in Tunisia 1943.jpg

Spitfire Vc(trop), equipped with Vokes filters and disc wheels, operated by 417 Squadron RCAF in Tunisia during 1943.

Throughout production, continuous refinements were implemented. Malcolm-manufactured "blown" cockpit canopies were introduced to enhance pilot headroom and field of vision. Many mid-to-late production Vbs—and all Vcs—adopted an improved windscreen assembly originating from the Mk III, featuring an integrated bullet-resistant central panel and flat side panes. Due to the increased height of the rear windscreen frame compared to earlier models, these later cockpit canopies were not interchangeable and could be distinguished by their wider rear framing.

Propeller types varied based on manufacturing location: Supermarine and Westland-produced Vbs and Vcs utilized 10 ft 9 in (3.28 m) diameter three-bladed de Havilland constant-speed propellers with narrow metal blades. Conversely, Castle Bromwich-built variants employed wide-bladed Rotol constant-speed propellers of either 10 ft 9 in (3.28 m) diameter with metal blades or, in later production runs, slightly smaller 10 ft 3 in (3.12 m) diameter versions fitted with broader "Jablo" compressed wood blades. Rotol spinners were longer and more pointed than their de Havilland counterparts, extending overall length by approximately 3.5 in (8.9 cm). The use of Rotol propellers contributed to modest speed gains above 20,000 ft (6,096 m) as well as improvements in service ceiling performance. Numerous Spitfire VBs incorporated "gun heater intensifier" systems attached to the exhaust stacks; these delivered additional heated air into gun bays via a small tubular intake at the front of the first stack and a narrow pipe connecting to the engine cowling at the rear.

The Vb series marked the first Spitfires capable of carrying specially designed slipper-type drop tanks mounted beneath the wing center section. Small hooks placed just ahead of the inboard flaps secured these tanks; upon release, the hooks engaged with the trailing edge of the tank to swing it clear away from the fuselage.

Following the introduction of the formidable Focke-Wulf Fw 190 in August 1941—which initially outperformed the Spitfire—the development of an interim Mk IX was accelerated. To address this new threat at lower altitudes, clipped wingtips became an optional feature on production Vbs for the first time, reducing wingspan to 32 ft 2 in (9.8 m). These clipped wings improved roll rate and low-altitude speed. Various Merlin 45/50 family engines were installed, including the Merlin 45M variant featuring a smaller "cropped" supercharger impeller and increased boost pressure up to +18 lb. This powerplant produced 1,585 hp (1,182 kW) at 2,750 ft (838 m), enhancing the L.F VB's peak climb rate to approximately 4,720 ft/min (21.6 m/s) at around 2,000 ft (610 m).

File:Spitfire VBs 40 Sqn SAAF with pilots at Gabes 1943.jpg

Vb Trop from 40 Squadron SAAF, outfitted with streamlined Aboukir air filters, broad-bladed Rotol propeller measuring 10 ft 3 in (3.12 m) in diameter, and clipped wings.

The Mk Vb(trop) variant (type 352) is distinguishable by its prominent Vokes air filter mounted beneath the nose; however, this filter reduced airflow velocity to the supercharger causing a decrease in top speed by about 8 mph (13 km/h) and climb rate by roughly 600 ft/min (3.04 m/s). Despite these drawbacks, performance losses were deemed acceptable for desert operations. Additional features included an enlarged oil tank and desert survival equipment installed behind the pilot's seat along with a revised desert camouflage pattern. Numerous Vb(trop)s underwent modifications at RAF Maintenance Unit-103 depots located at Aboukir, Egypt, where factory-new aircraft were upgraded prior to squadron deployment; here, original Vokes filters were replaced with locally produced Aboukir-style filters that were lighter and more aerodynamically efficient. Photographic evidence shows two distinct filter designs: one with a bulky square housing and another more streamlined version. These modified aircraft typically carried wide-blade Rotol propellers paired with clipped wings.

Mk Vc and Vc (trop) (Types 349 and 352/6)

In addition to incorporating many of the standard Mk V characteristics, this variant featured several significant improvements over the earlier Mk V models, most of which were initially trialed on the Mk III. Among these enhancements were a reinforced and re-stressed fuselage frame and a redesigned windscreen, which was also adopted on certain Vb Spitfires. The Vc model introduced the Type C or "Universal" wing combined with an updated main landing gear; the upper surfaces of these wings had prominent, bulging fairings designed to accommodate the ammunition feed motors for two Hispano cannons. Since fitting two cannons was uncommon, these fairings were subsequently downsized into more streamlined contours. A deeper radiator housing was installed beneath the starboard wing, while a larger oil cooler with an extended, kinked air outlet was placed under the port wing. Additional armor plating was also incorporated to shield the underside of the pilot's seat and the wing ammunition compartments.

File:British Spitfire takes off from USS Wasp (CV-7).jpg

Spitfire Vc taking off from Wasp during Operation Bowery. This represents part of the initial batch of Spitfires delivered to the RAF stationed in Malta. A 60-gallon "slipper" type drop tank was attached beneath the center section, and the upper surfaces were painted blue or blue/gray to aid camouflage during the extended flight over the Mediterranean.

The first Spitfire adapted for bomb carriage was a Malta-based Vc, designated EP201, capable of carrying a single 250 lb bomb beneath each wing. In correspondence with the Air Ministry, Air Vice Marshal Keith Park stated that "[w]e designed the bomb gear so that there was no loss of performance when the bombs were dropped. Unlike the Hurricane bomb gear our Spitfire throws away all external fittings with the exception of a steel rib which protrudes less than one inch from the wing."

One particular Vc (trop), BP985, underwent modifications by 103 MU to serve as a high-altitude interceptor targeting Ju 86P photo reconnaissance aircraft operating over Allied naval installations in Egypt. This aircraft was stripped of all superfluous weight, including removal of armor plating and Hispano cannons, while the Merlin 46 engine’s compression ratio was increased by altering the cylinder block. It was equipped with a four-bladed de Havilland propeller, an Aboukir filter, a larger 9.5-gallon oil tank, and extended wingtips.

The Mk Vc (trop) marked the first Spitfire variant deployed overseas in substantial quantities. Most served with Allied air units across the Mediterranean theater—including North Africa—as well as in Burma and Australia with No. 1 Fighter Wing RAAF. Initially, in Australia, this model experienced frequent mechanical failures caused by corrosion in engine cooling pipes that had been shipped empty and exposed to salt air during transit from the UK.

Following the introduction of the Mk IX, only a limited number of Mk Vc Spitfires engaged in combat operations over Europe.

Spitfire V production and international deliveries

A total of 300 Mk Vc (trop) units were dispatched to Australia for use by the RAAF, with the initial batch arriving toward the end of 1942. The Soviet Union received 143 Spitfire Vb aircraft, including some converted from Mk II models. Portugal was supplied with two separate shipments of Spitfire VBs: the first, comprising 33 refurbished former RAF planes, began arriving in early 1944, followed by a final delivery of 60 predominantly clipped-wing LF Mk Vbs in 1947. These aircraft were all upgraded with TR 9 HF radios but lacked IFF systems. The Portuguese Spitfires remained operational until their retirement in 1952. Additionally, twelve units were delivered to the Royal Egyptian Air Force.

In 1944, Turkey was provided with enough Spitfire Vb (trop)s to outfit a complete squadron. Some of these later received the larger, pointed rudder design developed for subsequent Merlin-powered Spitfires. These aircraft operated alongside German-supplied Focke-Wulf Fw 190A-3 fighters within the Turkish Air Force.

Overall production reached 6,479 aircraft, including 94 Mk Va models constructed by Supermarine; 3,911 Mk Vb variants (with 776 built by Supermarine, 2,995 at Castle Bromwich, and 140 by Westland); and 2,467 Mk Vc types (478 from Supermarine, 1,494 Castle Bromwich, and 495 Westland), plus an additional 15 PR Type F units manufactured at Castle Bromwich.

Daimler-Benz engine fitted Spitfire Vb

In November 1942, a Spitfire Vb marked EN830 NX-X from 131 Squadron was forced to land in a turnip field near Dielament Manor on Trinity Island, Jersey, which was under German occupation at that time. The aircraft was salvageable and subsequently underwent test flights bearing Luftwaffe insignia at the central research facility Erprobungsstelle Rechlin. During testing, it was proposed to replace the original Merlin engine with a Daimler-Benz DB 605A inverted V-12 powerplant. The plane was transferred to Daimler-Benz’s flight test center located at Echterdingen, near Stuttgart.

Upon removal of the Merlin engine, it was found that the fuselage cross-section closely matched that of the Messerschmitt Bf 110G’s engine nacelle. This allowed engineers to construct a new engine mount on the Spitfire’s fuselage frame to accommodate the DB 605 engine along with its cowling panels. The installation was completed using a propeller assembly and supercharger air intake sourced from a Bf 109G.

Additional modifications included replacing the original Spitfire cockpit instruments with German equivalents and converting the electrical system from a 12-volt setup to a German-standard 24-volt configuration. This Daimler-Benz powered Spitfire began flying in early 1944 and gained favor among German pilots until it was destroyed during a USAAF bombing raid on August 14, 1944.

Mk VI (Type 350)

File:Spitfire VI No 124 Sqn at North Weald c1942.jpg

Template:Center

When production of the Mk V began, concerns were rising that the Luftwaffe might soon deploy large numbers of very high-altitude bombers, such as the Junkers Ju 86, capable of flying beyond the effective range of most fighters at that time. This prompted the development of a new Spitfire variant with enhanced performance at high altitudes. On 17 February 1941, during a meeting at the RAE in Farnborough, the Air Ministry requested a Spitfire equipped with a pressurized cockpit able to maintain a pressure difference of 1 pound per square inch (69 hectopascals; 0.068 standard atmospheres) at an altitude of 40,000 feet (12,000 m). A compressor produced by Marshall Aerospace was selected for this purpose, and it was agreed that the sliding canopy could be replaced by a fixed canopy that could not slide open but could be jettisoned by the pilot if necessary.

The pressurized cockpit addressed the physiological challenges faced by pilots operating at extreme altitudes. Unlike modern airliners with fully pressurized cabins, the Mk VI’s modified cockpit provided only a 2 psi (140 hPa; 0.14 atm) pressure differential—twice the Air Ministry's original specification. To achieve this level of pressurization, both the forward and rear bulkheads of the cockpit were fully sealed, with control and electrical cables passing through specialized rubber grommets to maintain airtight integrity. The side cockpit door was replaced with an alloy panel, and the canopy was no longer designed to slide; externally, slide rails were absent. Once inside, pilots secured the canopy using four toggle fasteners and sealed it with an inflatable rubber tube. The canopy could be ejected in emergencies by pilot action. The windscreen used on production Mk VIs was identical to that fitted on Mk III and some Mk V models but featured an inward-opening clear-view panel on the port quarter window. This arrangement made an altitude of approximately 37,000 ft (11,000 m) feel like 28,000 ft (8,500 m) to the pilot, who still required an oxygen mask. Pressurization was maintained by a Marshall compressor mounted on the starboard side of the engine, supplied through a long intake beneath the starboard exhaust stubs. The Mk VI retained the Coffman cartridge starter with a small teardrop-shaped fairing positioned just ahead of this compressor intake.

Power came from a Rolls-Royce Merlin 47 engine turning a four-bladed Rotol propeller measuring 10 ft 9 in (3.27 m) in diameter; this new propeller design improved thrust in thin air conditions encountered at high altitudes. To optimize airflow over the wings’ tips, standard rounded wingtips were replaced with elongated pointed tips, extending wingspan to 40 ft 2 in (12.2 m). Apart from this modification, the wings conformed to Type B specifications.

The Mk VI achieved a top speed of 356 mph (573 km/h) at 21,800 ft (6,600 m), but due to limitations inherent in its single-stage supercharger, maximum velocity dropped to 264 mph (425 km/h) at 38,000 ft (12,000 m). Its service ceiling reached 39,200 ft (11,900 m).

Ultimately, fears of a prolonged high-altitude offensive by the Luftwaffe did not come to fruition, resulting in only 100 Mk VIs being produced by Supermarine. The variant was fully adopted by just two squadrons: No. 124 Squadron RAF and No. 616 Squadron RAF, although several others operated limited numbers as interim equipment. More frequently employed at lower altitudes where it was outclassed by standard Spitfires, it was found that modified Spitfire Vs could nearly match Mk VI performance at altitude. Pilots often flew with canopies removed due to excessive cockpit heat and concerns over emergency jettison reliability.

In 1943, five Mk VIs (registrations BS106, BS124, BS133, BS134, and BS149) underwent conversion into makeshift PR Mk.VIs by No. 680 Squadron RAF in Egypt. These aircraft were 'tropicalised' using bulky Vokes filters and similar equipment as found on Spitfire Vb (trop) variants and painted with desert camouflage patterns.

Though initially intended to counter high-flying Junkers Ju 86P reconnaissance aircraft—which had become less relevant—there arose a demand for pressurized photo-reconnaissance Spitfires capable of operating over Crete and Greece more broadly. Modifications were carried out by 103 MU at Aboukir: armaments were removed and vertical F8 cameras installed within the rear fuselage. These aircraft saw limited use during April and May 1943 before being retired by August. They represented the first pressurized photo reconnaissance Spitfires deployed by the RAF.

PR Mk XIII (Type 367)

The PR Mk XIII represented an advancement over the preceding PR Type G, retaining the same camera equipment but incorporating a new powerplant, the Merlin 32 engine, which was specifically optimized for operations at low altitudes. Its armament consisted of a modest loadout of 4 × .303" Browning machine guns. The initial prototype of the Mk XIII underwent testing in March 1943.

A total of twenty-six Mk XIII aircraft were converted from either the PR Type G, Mk II, or Mk V models. These aircraft were deployed primarily for low-level reconnaissance missions in the lead-up to the Normandy landings.

Production

Most early P.R. Spitfires originated from conversions of existing airframes and are not catalogued separately. Since the earliest Mk Vs were adapted from Mk I and some Mk II airframes, the first genuine production Spitfire V is documented accordingly.

Production by Mark

Mark	Manufacturer	Quantity produced	Remarks
Prototype	Supermarine	1	K5054. First flight on 5 May 1936.
Ia, Ib	Supermarine, Westland	1,567	Initial production Spitfire K9787 flew on 14 May 1938.
IIa, IIb	Castle Bromwich	921	First Castle Bromwich-built Spitfire P7280, June 1940.
III	Supermarine	2	Converted aircraft: N3297 from Mk I and W3237 from Mk V.
Va, Vb, Vc	Supermarine, Castle Bromwich, Westland	6,487	First Mk V; P8532 (Vb) flew in June 1941.
VI	Supermarine	100	Initial Mk VI AB136 flown December 1941.

External links

• Alan Le Marinel's Supermarine Spitfire resource
• Performance evaluations of the Spitfire
• Detailed records of Spitfire/Seafire serial numbers, manufacturing contracts, and aircraft histories
• Warbird Alley: Current information on operational Spitfires
• History of the K5054 Supermarine Type 300 prototype and production Spitfires
• NACA documentation on Spitfire Mk VA W3119
• Flight characteristics of the Spitfire VA
• Stall behavior analysis of the Spitfire VA
• Research on jet propulsion exhaust stacks Accessed: 29 January 2009.
• Spitfire Mk1 – Routine Inspection by Squadron 609