Deliveries of production Spitfire I's began in June 1938, two years after the first production contract had been placed . In those two years Supermarine laid out their Woolston factory for large-scale production and organized one of the largest subcontract schemes ever envisaged in Britain. Until that time, as it was becoming increasingly obvious that there was no limit to the likely demand for the Spitfire. It was also obvious that one factory alone was not going to be able to meet the demand even with sub-contracting. Large scale plans were laid during 1937 for the construction by the Nuffield Group of a large new shadow factory at Castle Bromwich near Birmingham for Spitfire production. On April 12,1938 a contract was placed for 1,000 Spitfires to be built at this new factory, of which the actual construction had not then even begun. In the following year, on April 29 further contracts were placed with Supermarine for 200 Spitfires and on August 9 for 450. When Britain went to war on September 3,1939 a total of 2,160 Spitfires were already on order.
Structurally the Spitfire was a straightforward design with a light alloy monocoque fuselage and a single spar wing with stressed-skin covering and fabric-covered control surfaces. The Spitfire was adapted from Reginald Mitchell's aesthetically pleasing 1925 F.7/30 design. To preserve the clean nose-cowling lines originally conceived by Mitchell, the radiator was located beneath the starboard wing with the smaller oil cooler causing some asymmetry beneath the port wing, and the carburetor air intake under the center fuselage. A DeHavilland two-blade wooden fixed-pitch propeller was employed by the prototype and the first Spitfire I's had the Airscrew Company's wooden fixed-pitch two-blade. Later a DeHavilland three-blade, two position propeller was adopted after trials on the first prototype. The new propeller gave a 5 mph increase in speed. In 1940 DeHavilland three-blade constant-speed propeller were substituted. Production Spitfires had a fixed tail wheel and triple ejector exhaust manifolds. The X80 HP Rolls-Royce Merlin II and later the Merlin III engine was installed.
The Spitfire I weighed 5,280 lb. had a wing loading of 24 lb./s. ft. and a fuel capacity of 85 Imperial gallons. Its maximum speed was 362 mph its maximum diving speed was 450 mph its initial climb rate was 2,500 ft./min. and it took 9.4 minutes to climb to 20,000 feet. Its combat range was 395 miles and its roll rate was 140 deg./sec. Standard armament in what was subsequently to become known as the A wing was eight 0.303-in. Browning machine-guns with 300 rounds of ammunition. The speed of the Spitfire I was marginally higher than that of its principal opponent the Luftwaffes Messerschmitt Bf 109E and it was infinitely more manaeuvrable than the German fighter although the Bf 109E could out climb and out dive the British fighter and its shell-firing cannon had a longer range than the Spitfire's machine-guns.
The 1,175 h.p. Merlin XII was adopted as the standard power plant in the Type 329 Spitfire II with a Rotol three-blade propeller and 73 lb. of amour protection but this variant was otherwise similar to the Spitfire I. Deliveries commenced in 1940 the Spitfire II having followed the Mark I on the production lines and becoming the first major production variant to be delivered from Castle Bromwich. In 1941 the Merlin 45 series of two-stage single-speed engines was adopted and the Type 349 Spitfire V so powered followed the Mark II into production and service.
The Spitfire V loaded weight had crept up to 6,417 lb. and the maximum speed up to 369 mph. The first squadron to fly the Spitfire V was the No. 92 and in March 1942, fifteen Spitfire VBs which had been shipped to Malta on H.M.S. Eagle, became the first Spitfires to serve outside Europe. Spitfires of this Mark were later to serve in the Western Desert and the Pacific and Burma areas.
In the normal course of development, means were sought to increase the altitude performance of the Spitfire which was inferior to that of the Messerschmitt Bf 109E . This called for two principal modifications, the introduction of a pressurized cabin and the use of an engine suitably rated for higher altitude. The first version of the Spitfire so equipped was the Mark VI derived directly from the Mark VB as a result of work on pressure cabins at the Royal Aircraft Establishment and Supermarine during 1940-41. At the R.A.E., R7120 was fitted with a Merlin 47 (the high rated version of the Merlin 45) with a four-blade Rotol propeller with Jablo blades and a pressure cabin. The same engine was employed by the 100 Spitfire VI (Type 350) fighters built by Supermarine the first two of these AB176 and X4942 serving as prototypes. The production Spitfire VI also had an increase in wing area to improve controllability at high altitudes the wing being of pointed planform with a span of 40 ft. 2 in. The pressure cabin was contained between the bulkheads fore and aft of the cockpit and a special non-sliding hood was fitted to simplify the sealing problem. A Marshall blower provided a cabin differential of 2 lb./s. in. reducing apparent altitude from 40,000 feet to 28,000 feet. In other respects including armament the Spitfire VI was similar to the Mark VB.
The Spitfire VII (Type 351) was a more extensive re-design for high-altitude work and was the first of the Spitfire series intended to make use of the two speed Merlin 60 series of engines. These two-stage engines were coupled with a re-designed cooling system which showed itself in the enlarged air intake under the port wing matching that to starboard. The wing outline remained similar to that of the Spitfire VI but the ailerons were reduced in span. The chord and area of the rudder were increased and the elevator horn balance was extended. Structural changes were made to the fuselage to take the increased engine loads and a double-glaze sliding hood was fitted to the cockpit. The retractable tail wheel first developed for the Spitfire III was applied in production for the first time on the Mark VII and the universal C -type wing was employed. Maximum speed jumped by 44 m.p.h. to 408 m.p.h. and normal loaded weight climbed to 7,875 lb.
Production of some 40 different variants of the Spitfire took place throughout the war and after. They served in every combat area, operating as fighters, fighter-bombers, reconnaissance aircraft and carrier-based fighters with the Royal Navy. Griffon engines replaced Merlins after a time, and the Spitfire XIX reconnaissance version became the fastest of all the wartime Spitfires with a speed of nearly 748 km/h (460 mph). The last Spitfire was built in 1947. As a fighter, at all altitudes it had proved superb, while continuous edges gained firstly by German Bf 109s and Focke Wulfs 190s and then by different versions of the Spitfire led to closely-matched battles throughout the war.
From: Larry Dwyer
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