Evolution of an Icon
The Spitfire Series
Spitfire Mk I
The story of the Spitfire began in 1931 with the Air Ministry's specification F.7/30 - Operational Requirement 1 - which called for a fighter capable of 250 mph. R. J. Mitchell and his team at Supermarine responded with a design that would first fly in February of 1934 - the Type 224. She was a chunky ship to say the least, not reminiscent at all of the streamlined lineage that would follow, and she duly lost out in competition to the Gloster Gladiator.
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Re-thinking his approach, Mitchell looked to Supermarine's seaplane racers, which had proven so successful through Schneider Trophy events. Modifying these designs led to another proposal before the end of 1934 - the Type 300.
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When this was not accepted by the Air Ministry either, perhaps a less committed engineer might have moved on to other projects - but not Mitchell. More changes to the Type 300 now came, including an enclosed cockpit and thinner wings, but perhaps the most significant alteration was the inclusion of the Rolls-Royce PV XII V-12 engine - a power plant that would later be known as the Merlin.
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Just before the end of the year, the Air Ministry finally took note, awarding ten thousand pounds to Supermarine for the development of the Type 300. The following Spring, the Operational Requirements Section approached Mitchell regarding a new upcoming specification - F.10/35 - which would call for a fighter with a minimum of six, preferably eight machine guns, and a reduced fuel capacity to save weight and increase speed.
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On 5th March 1936, four months after Sir Sydney Camm's Hawker Hurricane had made its maiden flight, the newly christened Spitfire took to the skies.
Prototype K5054
By mid-May, K5054 had clocked a top speed of 348 mph and was handed over to the Aeroplane and Armament Experimental Establishment (A&AEE). In a clear vote of confidence, before receiving the full report on the aircraft from A&AEE, the Air Ministry placed an order for 310 Spitfires.
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Many at the Ministry likely wondered if their faith had been misplaced when, 23 months later, the first Spitfire still had not appeared from the production line. Supermarine were not themselves a large company, parented as they were by Vickers-Armstrong, and the Spitfire contract was only one among many for other types. Sub-contracting was the obvious solution and should have quickly enabled production, but Vickers-Armstrong were slow to distribute to other companies the design materials needed to complete the work.
An unhappy Air Ministry decided that the existing order for 310 aircraft would be the limit of the run, after which Supermarine could focus on other types. But the company had great faith in their machine, and managed to convince the Ministry that further production delays would be a thing of the past. They were successful in this argument, so much so that a further order for 1,000 Spitfires was placed. At this point, unbeknownst to all, the Münich Crisis was only a few months away.
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August 1938, and the Spitfire entered service with the RAF. 19(F) Squadron would be the first to receive them.
Spitfire Mk Is of 19(F) Squadron in October 1938 (you'll also find this image on the cover of The Eagle and the Empire)
As the Spitfire joined the RAF's frontline strength, the crisis around the Sudetenland was coming to a head. War was still a year away, although of course no-one could know that, and while the Spitfire was a capable machine and perfect stablemate to the Hurricane, in the complex of the Bayerische Flugzeugwerke an opponent was being developed from combat experience in Spain that would prove a true test for the Spitfire - the Bf 109 Emil.
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A word on propellers - it's an interesting aside to the Spitfire story and a crucial detail that made the aircraft (and also the Hurricane) competitive with Luftwaffe fighters. Almost the first hundred Spitfires had been delivered with fixed-pitch twin-blade wooden propellers - essentially manual cars with only one forward gear. It was quite obvious at the time this was a limitation to the Spitfire's performance and so the De Havilland two-pitch three-bladed propeller rapidly became the standard and was the case for new production aircraft as the Phoney War in the west came to an end.
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But the Spitfire now lagged behind the Bf 109 in this respect. While the RAF fighter could choose between two selections, fully fine or a coarser pitch for cruise, the Luftwaffe Emil provided full propeller pitch control authority to the pilot through the use of a manual switch on the instrument panel, using the switch to drive the propeller to finer or coarser pitch as desired. While this control was not at first automatic (akin to a governor), it did provide a Bf 109 pilot with greater authority to make more efficient use of his propeller.
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This was a problem for Hurricanes too - stationed in France as Blitzkrieg began, they urgently started to receive Rotol (Rolls-Royce / Bristol) Constant Speed Units for their propellers. De Havilland proposed to do the same for the RAF's Spitfires, all of which were based in the UK, and they undertook the work in earnest in the Spring of 1940 as Hitler's armies crashed across French territory.
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A Spitfire with a Constant Speed Unit could accelerate faster, take-off in a shorter distance, climb more quickly and attain a higher top speed than its fixed-pitch two-blade forbears. Through a herculean effort, De Havilland managed to retrofit almost the entire frontline complement by the time the Battle of Britain approached its height in August. Even a few months of delay could have proven catastrophic...
Mk Ia of 602 Squadron
Even before the 'Phoney Way' had come to an end, the installation of Hispano 20mm cannons into the Spitfire was under consideration. Supermarine's acting Chief Designer Joseph Smith, who had taken over after R. J. Mitchell's death and after Mitchell's deputy had been expelled on account of his German born wife, proposed a design in which the cannons were mounted on their sides so that they might be installed within the wings, with only small blisters needed to accommodate the drums of ammunition in the locations where they would otherwise protrude from the fuselage. 19(F) Squadron would be first to trial the Hispano-equipped Spitfire Mk Is, and those armed with the 'standard' eight Browning MGs became type Ia while those with cannon were type Ib. The Squadron's experience with the new cannon was something less than satisfactory, with only a small number of aircraft on a sortie typically able to fire off their entire complement of ammunition without experiencing problems.
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The importance of the Spitfire as an interceptor was obvious, but it would also revolutionise another air power role - photographic reconnaissance.
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To date the preserve of twin-engined light and medium bomber types, which the RAF had all but assumed would continue to undertake the task, before the end of 1939 it was proposed that fast, lightweight fighters might be better platforms to undertake such work. The first Photographic Reconnaissance (PR) Spitfire versions then came into being, taking a Mk I aircraft and removing armament and radios to permit the addition of extra fuel and cameras. A small number were converted during the height of the Battle of Britain, but the pressing need for frontline fighter aircraft meant that the demand for PR variants would only really be satisfied once the intensity of the conflict had ebbed.
Spitfire Mk IIa
By April 1941, all Mk Is on the RAF's frontline had been replaced by the Mk II, which also came in flavours of IIa and IIb dependent upon whether armed with 20mm cannon - by this time much of the jamming issue had been resolved. The Mk II brought the Merlin XII, a significant upgrade from the Merlin III of the Mk I - power output was increased from just over a thousand horsepower to nearly twelve hundred. Paired with the new Rolls-Royce Bristol (Rotol) manufactured 'wide-blade' propeller, climb rate was much improved over the Mk I.
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It's at this point that the complex assigning of marks and sub-types for the Spitfire begins to kick into gear. There are some staggeringly extensive reference works out there and I certainly won't try to replicate that content in a single article, so forgive me dear reader as we largely overlook the Mk III and examine the version that several late Mk IIs became - the Spitfire Mk V.
Spitfire Mk Vc AR501 of the Shuttleworth Collection
The Mk V was in large part a response to a new Luftwaffe threat - extremely high altitude incursions, flown by the new Ju 86P. Fundamentally the Mk V was a Mk I or Mk II upgraded to utilise the new Merlin 45 engine. Horsepower had been increased once again, this time to over fourteen hundred at takeoff.
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But on the other side of the Channel, the Third Reich had not been idle in their own developments. Kurt Tank, Chief Designer at Focke-Wulf, had realised by late 1941 his vision for a radial-engined fighter to complement, perhaps even supplant, the Bf 109, which was felt to be close to its evolutionary limit. The Fw 190 would prove an unpleasant new opponent for the Royal Air Force as Fighter Command pursued an offensive strategy to try to gain air superiority in north-western Europe.
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At best, the Spitfire Mk V found itself on broadly equal terms with the new BMW 801 powered fighter. At worst, against a Luftwaffe veteran of two years of war, a Mk V pilot could easily find himself outclassed. Some urgent modifications were made - one example being the 'clipping' of the Mk V's wings to improve roll rate - but in fact, the next iteration of the Spitfire was imminent and would, in short order, see the balance tilted once again.
Spitfire Mk IX MH434
Once again it would be the next generation of Merlin engine that held the key to pushing the Supermarine fighter still further - the Merlin 61 and its two-stage supercharger.
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In April 1942, the Air Fighting Development Unit tested the first Mk IX example, which was a Mk Vc modified to use the new engine. There was much about the new aircraft to praise:
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'The performance of the Spitfire IX is outstandingly better than the Spitfire V especially at heights above 20,000 feet. On the level the Spitfire is considerably faster and climb is exceptionally good. It will climb easily to 38,000 feet and when levelled off there can be made to climb in stages to above 40,000 feet by building up speed on the level and a slight zoom. Its manoeuvrability is as good as a Spitfire V up to 30,000 feet and above is very much better. At 38,000 feet it is capable of a true speed of 368mph and is still able to manoeuvre well for fighting'