Structurally the plane 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 design 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 plane 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 planes had a fixed tail wheel and triple ejector exhaust manifolds. 4 The PV.12 engine which became the X80 HP Rolls-Royce Merlin II and later the Merlin III engine was installed.

The plane weighed 5,280 lb. had a wing loading of 24 lbs/ft sq. 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 known as the A wing was eight 0.303-in. Browning machine-guns with 300 rounds of ammunition. The speed of this plane I was marginally higher than that of its principal opponent the Luftwaffes Messerschmitt Bf 109E and it was infinitely more maneuverable 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 this plane's machine-guns. 6

The 1,175 hp Merlin XII was adopted as the standard power plant in the Type 329 with a Rotol three-blade propeller and 73 lb. of armour protection but this variant was otherwise similar to the earlier version. Deliveries of the Mk IIs began in 1940 following the Mark I production lines and became the first major production variant to be delivered from Castle Bromwich. By April 1941 650 Mk IIs had left the Bromwich factory and the changeover was complete. Most of the Mk Is were then relegated to the training role. 7 In 1941 the Merlin 45 series of two-stage single-speed engines was adopted and the Type 349 so powered followed the Mark II into production and service. The planes 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 VBs which had been shipped to Malta on H.M.S. Eagle, became the first to serve outside Europe. Aircraft 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 plane 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 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 the manufacturer 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 VI (Type 350) fighters built by the manufacturer the first two of these AB176 and X4942 serving as prototypes. The production VI version 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 VI version was similar to the Mark VB. 9

The VII (Type 351) was a more extensive re-design for high-altitude work and was the first of the 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 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 III version 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 mph to 408 mph and normal loaded weight climbed to 7,875 lbs.

Production of some 40 different variants of the plane 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 XIX reconnaissance version became the fastest of all the wartime planes with a speed of nearly 460 mph (748 km/h). The last aircraft 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 plane led to closely-matched battles throughout the war.