Spitfire Mk I Specifications
Crew: Pilot only
Powerplant: One 1,030 hp Rolls-Royce Merlin III twelve-cylinder liquid-cooled engine
Span: 36 ft 10 in (11.23 m)
Length: 29 ft 11 in (9.12 m)
Max Speed: 367 mph (582 km/h) at 18,600 ft (5,669 m)
Armament: Eight .303 in (7.7 mm) Browning machine guns mounted in wings
Photo Description: Spitfire Mark IA, X4179 QV-B, of No. 19 Squadron, on the ground at Fowlmere, Cambridgeshire, as the pilot, F/O Francis N Brinsden, undertakes a cockpit check prior to take off, 21 September 1940.
The Supermarine Spitfire was a British single-seat fighter aircraft that served as a cornerstone of the Royal Air Force (RAF) and several Allied air forces during the Second World War. It was conceived as a short-range, high-performance interceptor and designed by Reginald J. Mitchell, Chief Designer at Supermarine Aviation Works, a subsidiary of Vickers-Armstrongs. Development of what became the Spitfire began in 1934 as the private venture Type 300, following the failure of Supermarine’s earlier Type 224 prototype to meet Air Ministry expectations.
Drawing on Supermarine’s experience with the Schneider Trophy-winning racing seaplanes of the late 1920s and early 1930s, Mitchell’s design featured a streamlined, semi-monocoque all-metal fuselage and distinctive elliptical wings. These thin, aerodynamically efficient wings not only housed the aircraft’s armament but also gave it a high top speed and excellent handling characteristics. The prototype, powered by the new Rolls-Royce PV-12 engine—which would later become the famed Merlin—was armed with eight wing-mounted .303 inch (7.7 mm) Browning machine guns. On 1 December 1934, the Air Ministry issued contract AM 361140/34, authorising £10,000 for a single prototype, which first flew as K5054 on 5 March 1936 at Eastleigh Aerodrome. Mitchell died of cancer just three months later, but his legacy was carried forward by Joseph Smith, who became Chief Designer at Supermarine and oversaw the Spitfire’s continued development.
Following successful trials at Martlesham Heath, the Air Ministry placed an initial order for 310 aircraft. The Spitfire Mk I officially entered service with No. 19 Squadron at RAF Duxford on 4 August 1938. Fast, powerful, and highly manoeuvrable, the Spitfire was a favourite among pilots. The early variants benefited from a bubble-style canopy, which gave excellent all-round visibility, and its performance was further improved with the introduction of constant-speed propellers and the increased availability of 100-octane aviation fuel from the United States. By the summer of 1940, eighteen squadrons were equipped with Spitfires in time for the Battle of Britain.
During the Battle of Britain, the Spitfire became a national symbol of resistance and technical excellence. Its status was elevated in part by the “Spitfire Fund,” a high-profile campaign spearheaded by Lord Beaverbrook, the Minister of Aircraft Production, which encouraged public donations for fighter production. However, due to early production bottlenecks, the more numerous Hawker Hurricanes bore the brunt of the fighting, accounting for around 55% of enemy aircraft destroyed by Fighter Command. Spitfires were credited with downing 529 enemy aircraft during the battle, at the cost of 230 of their own. Spitfire squadrons were generally tasked with engaging German escort fighters such as the Messerschmitt Bf 109, allowing the Hurricanes to attack the slower bombers.
In terms of performance, the Spitfire and the Bf 109 were closely matched. While the Bf 109 had better climb and dive characteristics, the Spitfire had superior manoeuvrability in level flight and tighter turning ability. One notable drawback of early Spitfires was their carburettor system, which caused the engine to cut out under negative-G manoeuvres. Pilots learned to half-roll their aircraft before diving, a workaround until engineer Beatrice Shilling developed a simple but effective restrictor—“Miss Shilling’s orifice”—to regulate fuel flow and resolve the issue.
In August 1940, the improved Spitfire Mk II entered service. It was equipped with the more powerful 1,175 hp Rolls-Royce Merlin XII engine and produced exclusively at the Castle Bromwich Aircraft Factory, a large-scale “shadow factory” established under the direction of Lord Nuffield. The Mk II featured a Rotol wide-blade constant-speed propeller, improving low-altitude speed by around 6–7 mph and enhancing the aircraft’s climb rate. While the added equipment marginally reduced its top speed compared to the lightest Mk I models, the Mk II offered improved overall combat effectiveness.
Most Mk I and Mk II Spitfires were armed with eight .303 inch Browning machine guns, carrying a total of 2,800 rounds—roughly 15 seconds of continuous fire. However, the effectiveness of this armament declined as Luftwaffe bombers began incorporating more armour protection. The RAF tested new ammunition types, including the De Wilde incendiary bullet, which offered some improvement, but attention quickly turned toward mounting heavier weapons. In mid-1940, No. 19 Squadron began trials with Spitfires fitted with two 20 mm Hispano-Suiza cannon, designated the Mk IB. These early installations, which used drum-fed cannons mounted sideways inside the wings, proved unreliable—often jamming after a single shot. Despite these issues, refinement continued, and by late 1940, improved versions of the Mk IB, with two cannon and four machine guns, entered service alongside the standard Mk IA variant.
The Spitfire’s legacy was established not only by its graceful lines and engineering excellence but also by the critical role it played in the defence of Britain. As the war progressed, the aircraft would be further developed into a wide range of variants and serve in multiple theatres, but it was during the summer of 1940 that the Spitfire etched its name into aviation history.