The British Supermarine Spitfire was the only Allied fighter aircraft of the Second World War to fight in front line service from the beginnings of the conflict, in September 1939, through to the end in August 1945.

[1] 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 called for.

To keep cold air from blowing in via the muzzle openings in the leading edge, they were sealed with red fabric adhesive tape by ground crew while loading the ammunition trays.

Only one armament suite could be fitted to a Spitfire with the B-type wing: Two 20 mm Hispano Mk II cannon, each with a 60-round drum, and four .303 caliber Browning machine guns in the outer positions, with 350 rpg.

The stronger undercarriage legs were angled 2 inches (5.08 cm) forward when extended, making the Spitfire more stable on the ground and reducing the likelihood of the aircraft tipping onto its nose.

[5] The D type was modified for use on unarmed, long-range photo-reconnaissance versions of the Spitfire, such as the PR Mk Id (PR versions described in more detail below), with weapon bays left empty, and the relatively heavy-skinned leading edge wing structure ahead of the main spar converted to integral auxiliary fuel tanks capable of carrying 66+1⁄2 Imperial gallons (300 L) in addition to that stored in the fuselage tanks ahead of the cockpit.

[11] The Mark numbers did not necessarily indicate a chronological order; for example, the Mk IX was a stopgap measure brought into production before the Mks VII and VIII.

One major change was to the Merlin engine's cooling system, with the adoption of ethylene glycol coolant together with a ducted radiator based on the work of Frederick Meredith at the Royal Aircraft Establishment, Farnborough.

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.

[20][nb 1] 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.

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.

[28] 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.

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.

The system employed unlocking pins, actuated by cables operated by the pilot pulling a small, red rubber ball mounted on the canopy arch.

[51] In August 1939, Flying Officer Maurice Longbottom, inspired by Sidney Cotton, filed a memorandum Photographic Reconnaissance of Enemy Territory in War with RAF Headquarters.

In the memorandum Longbottom advocated that airborne reconnaissance would be a task better suited to fast, small aircraft which would use their speed and high service ceiling to avoid detection and interception.

[51] 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.

[nb 7] Two F24 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.

[54] In the Mk I PR Type B (also known as Medium Range [MR]) conversions which followed, the F24 camera lenses were upgraded to an eight-inch (203 mm) focal length, giving images up to a third larger in scale.

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.

[61] A feature of most PR Spitfires were the specially modified "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.

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.

[77] He was shot down in this aircraft (possibly by friendly fire) during a "Circus" (a wing of fighters escorting a small number of bombers) over Northern France on 9 August 1941 and spent the rest of the war as a POW.

Some late production Vbs and Vcs were fitted with six shorter exhaust stacks per side, similar to those of Spitfire IXs and Seafire IIIs; this was originally stipulated as applying specifically to Vb(trop)s.[79] 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.

Many mid to late production Vbs – and all Vcs – used the modified, improved windscreen assembly with the integral bullet resistant centre panel and flat side screens introduced with the Mk III.

[91]" 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, while the compression ratio of the Merlin 46 was increased by modifying the cylinder block.

The Vc initially suffered a high rate of mechanical failure in Australia, due to corrosion in engine cooling pipes that were unfilled and exposed to salt air, while being shipped from the UK.

[64] 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, under German occupation at the time.

[100] To achieve this, the forward and rear cockpit bulkheads were completely enclosed, with all control and electrical cables exiting though special rubber sealing grommets.