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 is a British single-seat fighter that was used by the Royal Air Force and many other Allied countries during the Second World War. The Spitfire was designed by Reginald Joseph Mitchell, Chief Designer at Supermarine Aviation Works, originally as a private venture, but the British Air Ministry quickly became interested and a specification, F.37/34, was issued to cover the purchase of a prototype for evaluation. Mitchell’s design drew heavily on experience gained with the Schneider Trophy-winning Supermarine seaplanes in the late 1920s and early 1930s. The combination of a streamlined, semi-monocoque fuselage of light all-metal construction and thin elliptical wings enabled the Spitfire to have a higher top speed than several contemporary fighters. The aircraft was powered by the new Rolls-Royce PV-12 engine, later known as the Merlin, and armed with eight wing-mounted .303 in (7.7 mm) Browning machine guns. Mitchell lived just long enough to see the prototype, K5054, fly for the first time on 5 March 1936 at Eastleigh Aerodrome before dying of cancer three months later. He was succeeded as Chief Designer at Supermarine by Joseph Smith, who oversaw the further development of the Spitfire. Following successful test flights at Martlesham Heath, the Air Ministry placed an order for 310 aircraft. The Spitfire Mk I entered RAF service with No. 19 Squadron at RAF Duxford on 4 August 1938. Much loved by its pilots, the new fighter was fast, powerful, and highly manoeuvrable. The bubble canopy gave the pilot excellent visibility. The performance of the aircraft was enhanced further by the introduction of the constant speed propeller and the increased availability of 100 octane fuel from the United States. By July 1940, an additional eighteen RAF squadrons were equipped with the Spitfire.

During the Battle of Britain, the Spitfire became a symbol of national defiance and achieved legendary status mainly due to the famous “Spitfire Fund” organised and run by Lord Beaverbrook, the Minister of Aircraft Production. However, initial production delays meant that the more numerous Hawker Hurricane shouldered a greater proportion of the burden against the Luftwaffe and shot down around 60% of enemy aircraft credited to Fighter Command. Whenever possible, Spitfires were used to counter the German escort fighters whilst the Hurricane squadrons attacked the slower bomber formations. The Spitfire and its main adversary, the Messerschmitt Bf 109, were well-matched in overall performance. The Bf 109 could climb and dive faster than the British fighter but was less maneuverable. In a dogfight, the Spitfire was unable to nose down into a deep dive without the engine temporarily cutting out. This was due to fuel being forced out of the carburetor by negative g-forces. RAF fighter pilots soon learned to half-roll their aircraft before diving to pursue their opponents. The issue was later resolved by “Miss Shilling’s orifice”, a small metal disc similar to a metal washer that restricted fuel flow to the carburetor.

In August 1940, the Spitfire Mk II entered service with the more powerful 1,175 hp Rolls-Royce Merlin XII engine. This was the first version to be produced exclusively by the huge new Lord Nuffield shadow factory at Castle Bromwich. All Mk IIs were fitted with Rotol manufactured wide-bladed propellers, which increased top speed by about 6–7 mph below 17,000 feet (5,200 m), and improved climb rate. Although combat capability was far better, maximum speed performance was still lower than that of early Mk Is due to all of the weight increases.

The majority of Mk Is and Mk IIs were armed with eight .303 in (7.7 mm) Browning machine guns carrying 2,800 rounds in total, enough for around 15 seconds of firing. It was discovered that the small calibre bullets were often unable to penetrate armour plating, which was being increasingly used in Luftwaffe aircraft to protect crew and vital areas. Although the introduction of the ‘De Wilde’ incendiary bullet increased overall effectiveness, the RAF had already begun to examine the heavier-calibre cannon as a solution. In June 1940, No. 19 Squadron received several Mk Is fitted with two 20 mm Hispano-Suiza cannon for operational trials. This version was referred to as the Mk IB, the Browning-armed Spitfires were retrospectively called the Mk IA. The initial installation had the guns mounted on their sides to fit the large drum magazines inside the wings. As a result, the Hispanos became unreliable, frequently jamming after only one shot. Work continued on a reliable cannon installation and by late 1940, a number of Mk IBs armed with two cannon and four .303 in machine guns entered service.