Graham M. Simons - Fighters under construction in World War Two : rare photographs from wartime archives

Original Caption: Supermarine Spitfire I eight-gun single-seater fighters, believed to be the fastest military aircraft in large-scale production in the world, on the final assembly line at Southampton. Rolls-Royce Merlin IIs are awaiting installation in the foreground. Despite its extreme performance the Spitfire is reasonably easy to build and even easier to fly.

The Supermarine Spitfire was a British single-seat fighter aircraft used by the Royal Air Force and many other Allied countries throughout the Second World War. It continued to be used into the 1950s both as a front line fighter and in secondary roles. It was produced in greater numbers than any other British aircraft and was the only Allied fighter in production throughout the war.

The Spitfire was designed as a short-range high-performance interceptor machine by R. J. Mitchell, chief designer at Supermarine Aviation Works (from 1928 a subsidiary of Vickers-Armstrong). Mitchell continued to refine the design until his death from cancer in 1937, whereupon his colleague Joseph Smith became chief designer. The Spitfires elliptical wing had a thin cross-section, allowing a higher top speed than several contemporary fighters. Speed was seen as essential to carry out the mission of home defence against enemy bombers.

A line of assembly fixtures for the monocoque main section of the fuselage.

Mitchells design aims were to create a well-balanced, high-performance bomber interceptor and fighter aircraft capable of fully exploiting the power of the Merlin engine, while being relatively easy to fly.

From the seventh frame, to which the pilots seat and (later) armour plating was attached, to the nineteenth, which was mounted at a slight forward angle just forward of the fin, the frames were oval, each reducing slightly in size and each with numerous holes drilled through them to lighten them as much as possible without weakening them.

A close up of one of the main fuselage assembly fixtures in which the assembly and plating of the monocoque portion was completed.

A rear view of the main assembly fixture with the fuselage framework in position, along with two women workers.

The Spitfires airframe was complex: the streamlined, semi-monocoque duralumin fuselage featured a large number of compound curves built up from a skeleton of frames, starting from the main engine bulkhead to the tail unit attachment frame. Aft of the engine bulkhead were five half-frames to accommodate the fuel tanks and cockpit.

The jig in which the attachment holes in the stub spars were finish-reamed and the wing-root fillet attachment holes drilled.

Once the frames were skinned the fuselage was transferred to a series of jigs for a number of machining processes.

These jigs formed a guide for the tools used in a machining operation.

Paired-up assembly fixtures for rear fuselage units.

The U-shaped frame 20 was the last frame of the fuselage proper and the frame to which the tail unit was attached. Frames 21, 22 and 23 formed the fin; frame 22 incorporated the tailwheel opening and frame 23 was the rudder post. Before being attached to the main fuselage, the tail unit frames were held in a jig and the eight horizontal tail formers were riveted to them.

A combination of fourteen longitudinal stringers and two main longerons helped form a light but rigid structure to which sheets of alclad stressed skinning were attached. The fuselage plating was 24, 20 and 18 gauge thickness in order of thickness towards the tail, while the fin structure was completed using short longerons from frames 20 to 23, before being covered in 22 gauge plating.

Spitfire Mk IIA, P7666, EB-Z, Observer Corps, was built by Castle Bromwich, and delivered to 41 Squadron on 23 November 1940.

First stage showing the structural framework almost completed.

Mitchell has sometimes been accused of copying the wing shape of the Heinkel He 70, which first flew in 1932; but as Beverly Shenstone, the aerodynamicist on Mitchells team, explained Our wing was much thinner and had quite a different section to that of the Heinkel. In any case it would have been simply asking for trouble to have copied a wing shape from an aircraft designed for an entirely different purpose.

A port wing structure in the main assembly fixture. The skin plating has been applied to the upper surface. Final stages of wing assembly were performed out of the fixture with the wing held in a felt-lined cradle.

A completed wing - with an undercarriage leg and wheel - sits in a felt-lined cradle awaiting to be turned through ninety degrees and placed on a flat trolley (right) before being moved to the Spitfire final assembly line. The spar roots were mounted at the correct assembly height.

Lowering the Rolls-Royce Merlin engine on to its mounting in the early stages of intermediate assembly.

The tubular engine mounting for the Spitfire was assembled in the inverted position.

The skins of the fuselage, wings and tailplane were secured by rivets and in critical areas such as the wing forward of the main spar where an uninterrupted airflow was required, with flush rivets; the fuselage used standard dome-headed riveting. From February 1943 flush riveting was used on the fuselage, affecting all Spitfire variants.