Spitfire Mk I of No 602 Squadron RAF at Drem March 1940
Supermarine secured its initial order for the Spitfire aircraft on June 3, 1936, which encompassed a total of 310 units. By September 3, 1939, when Britain officially entered into conflict with Germany, 2,160 Spitfires had been ordered and 306 had been delivered. At that time, production was occurring at a pace of one aircraft per day; however, deliveries were lagging due to the challenges associated with manufacturing the relatively intricate airframe.
The first production model of the Spitfire I took to the skies on May 14, 1938, and the aircraft was first deployed with No 19 Squadron at Duxford on August 4. Early models were equipped with the Merlin II engine and a two-bladed fixed-pitch propeller. Shortly thereafter, the Merlin III engine, which featured a three-bladed two-pitch de Havilland propeller, was introduced, followed by a three-bladed constant-speed propeller. This advancement in performance led to the conversion of early aircraft to the new propeller configuration in 1940.
By August 1940, a total of 19 squadrons within the RAF Fighter Command were operating Spitfire Is. The aircraft achieved its first aerial victories on October 16, 1939, when two Ju 88 bombers were downed over the Firth of Forth in Scotland.
Between 1938 and 1940, several modifications were made, including the replacement of the original flat canopy with a domed version to enhance pilot visibility, additional armor protection, and the installation of a gun camera. The initial Spitfire I, armed with machine guns, was retroactively classified as Mk.IA. It was succeeded by the Mk.IB, which initially featured two 20mm cannons with no machine guns, and later, a definitive ‘B’ wing with a combination of armaments. Trials with the cannons commenced in March 1939, and some aircraft were equipped with this armament during the Battle of Britain, though malfunctions were a concern. The first Mk.IB aircraft with the ‘B’ wing made its debut flight on August 20, 1940, and production of the Mk.IB reached 30 units.