Supermarine Spitfire. At Royal Air Force's service. Part two. Prototypes and early Spitfires.

 

After the disappointment of the Type 224, Mitchell and his design staff, began to draw cleaner designs using the experience with the Schneider Trophy seaplanes as a departing point. This, eventually led to the Type 300, which featured retractable undercarriage and a reduced wingspan. This original design was submitted to the Air Ministry but it was rejected, so it had to undergo a series of changes such as an enclosed cockpit, oxygen-breathing gear, smaller and slimer wings, and it was to be powered by the, back then, cutting edge Rolls-Royce PV XII V-12 engine, which was later commonly known as the Rolls-Royce Merlin. 
In November 1934, Mitchell was given permission from Vickers-Armstrong (Supermarine's parent company) to develop and reife the Type 300 and on 1st December he was given £ 10,000 from the Air Ministry for the construction of the Type 300, under contract AM 361140/34. 
On 5th March 1936 the first prototype, registered as K5054, took-off for the first time at Eastleigh Aerodrome, Hampshire. At the controls was Cpt. Joseph "Mutt" Summers, chief test pilot for Vickers, who praised the design. 
The initial prototype was later fitted with a new propeller and it was flown again on 10th March 1936, where the undercarriage was retracted for the first time and, after a fourth flight, a new engine was fitted. After overcoming many small failures and improving the design, it was flown again to RAF Martlesham Heath where it was handed to Squadron Leader Anderson of the Aeroplane & Armament Experimental Establishment (A&AEE) to be delivered to the Royal Air Force (RAF). Soon after the Air Ministry placed a production order for 310 Spitfires.
Although it was presented to the public on 27th June 1936, numerous problems hindered the mass production of the Spitfire and the first production aircraft wasn't completed until mid-1938 and it was delivered to No. 19 Squadron at RAF Duxford on 4th August 1938 and during the next weeks No. 66 Squadron also received the type, albeit at a slower pace. The next unit to receive the Spitfire was No. 41 Squadron at RAF Catterick and the first public sight of the Spitfire in RAF's colours and markings took place on Empire Air Day, on 20th May 1939. Later, more squadrons were gradually equipped with the type.
When World War 2 began, there were a total of 306 Spitfires in service with the RAF, seventy-one of them in reserve and 2.000 under manufacture with 36 written off due to accidents.
On 6th September 1939, shortly after the outbreak of the war, a friendly-fire incident known as the Battle of Barking Creek took place where two Hawker Hurricanes of 56 Squadron were shot down by Spitfires of 74 Squadron over the river Medway, Kent. One of the victims of this incident, P/O Montague Leslie Hulton-Harrop, was the first British pilot fatality of the World War II. This incident placed the manufacture of IFF (Identification Friend or Foe) equipment as a top priority.
On 16th October 1939 the Spitfire clashed against the German Luftwaffe for the first time when three aircraft from 602 and 603 Squadrons intercepted three Junkers Ju.88 belonging to 1./KG.30 over Rosyth (Fife, Scotland) trying to attack the cruiser HMS Southampton and HMS Edinburgh on the Firth of Forth. Two of the Ju.88 were shot down and another one was heavily damaged.

The PR (Photo-Reconnaissance) variants of the Spitfire, was a sub-variant dedicated for photo-reconnaissance missions. Before the war, military aerial doctrine dictated that the best option for long-range reconnaissance duties was to employ converted bombers, as they had defensive armament, however, it was soon discovered that Bristol Blenheims and Westland Lysanders were easy targets for German fighters so, following a memorandum made back in August 1939 by Flying Officer Maurice Longbottom, two Spitfires, N3069 and N3071 were released from RAF Fighter Command and sent to the Heston flight, a secret reconnaissance unit. 
Those two Spitfires were stripped from their armament and radio gear, two F24 ventral cameras were installed, heating equipment was added to prevent photographic cameras from freezing and the lenses from frosting. These Spitfires were later known as Spitfire Mk. I PR Type A and achieved a high speed of 390 mph (627 km/h) and were employed for the first in late 1939 to perform photographic reconnaissance flights over western Germany.

The Speed Spitfire was an racer-built variant which was built in late 1938 to achieve world speed records, mainly against German aircraft such as the Messerschmitt Bf.109 V13, Heinkel He.100 V2 and the Messerschmitt M.209 V1, which eventually got the prize achieving a top speed of 755.14 km/h (469.22 mph) on 26th April 1939.
It featured many design changes to make the type more aerodynamic and lacked radio equipment and armament to make it lighter. The Speed Spitfire was eventually handed to the RAF at the beginning of World War 2 where it was suited for photographic reconnaissance, given its high top speed. 

Sources:
1st https://en.wikipedia.org/wiki/Supermarine_Spitfire
2nd https://en.wikipedia.org/wiki/Supermarine_Spitfire_operational_history
3rd https://en.wikipedia.org/wiki/Supermarine_Speed_Spitfire
4th https://en.wikipedia.org/wiki/Supermarine_Spitfire_variants:_specifications,_performance_and_armament
5th https://en.wikipedia.org/wiki/Supermarine_Spitfire_(early_Merlin-powered_variants)