The Supermarine Spitfire had the measure of the Messerschmitt Bf 109 all throughout WWII, but then in 1941 the Germans did something different. A small, neat, radial-engined fighter appeared, and the Focke-Wulf 190 slaughtered the RAF’s premier interceptor.
It took Rolls-Royce and Supermarine about a year to produce the answer to the ‘Butcher Bird’, in the form of the Merlin 61 fitted into a long-nose airframe, and the combination became the Spitfire Mk IX. Perhaps the definitive Spitfire variant, the Mk IX, first flew on 20 September 1941, and remained in service from 28 July 1942 until the end of WWII and beyond.
The Merlin 61 had a two-stage supercharger with intercooler which boosted power from the 990 bhp of the Merlin II to 1560 bhp. The Spitfire IX was some 40 mph faster than the MkV, and could reach an altitude of 43,000 feet ~ 6,000 feet higher than the Spitfire Vb. The 190 was almost a match for the Spitfire IX below 20,000 feet, but above that altitude the Focke-Wulf was outclassed.
Suddenly it was the turn of Fw 190 pilots to be astonished , they were used to outflying Spitfires but the MkIX achieved superiority over both the Fw 190 and the Bf 109G. The unpleasant thing for Luftwaffe fighter pilots was the deadly Mk IX looked exactly like the Spitfire V they were used to shooting down.
The Spitfire IX was the best Spitfire. When we got the IX. we had the upper hand, which did for the 190s. ~ Johnnie Johnson.
Test Pilot Jeffrey Quill, who was instrumental in all Spitfire upgrades, described the Spitfire IX and it’s Rolls-Royce Merlin 61 engine as one of two quantum leaps in Spitfire performance during the war, (the other being the introduction of the Rolls-Royce Griffon engine).
Like many very powerful engines shoehorned into tiny fighters, the Merlin 61 was originally designed for use in high-altitude bombers, (see the Bf 109 D). Rolls-Royce were the world leaders in supercharger technologies and the Merlin 61 used two blowers in series, one feeding the other and separated by an intercooler. This crammed as much air as possible into the Merlin’s intake manifold. The Merlin 61 needed a big four-bladed propeller to absorb all that power, and the Spitfire IX needed a second underwing radiator to cool the intercooler. (Tricky for the Lutwaffe pilots to spot in the middle of a dogfight.)
The Spitfire IX weighed 600lbs more than the Mk V, and was usualy armed with two 20mm cannon and four .303 machine guns. There was a variant of the Merlin, the 66, which was used to power a low-altitude version of the Spitfire IX, the Spitfire LF IX. This was designed to better the Focke-Wulf 190 at low and medium altitudes, the 190’s preferred hunting ground. At 21,000 feet the LF Spitfire IX was 30 mph faster than the Fw 190, better in the climb and vastly more maneuverable.
The basic Mk IX also appeared as the modified photo reconnaissance Spitfire PR XI, which could cruise at 42,000 feet, well above the maximum altitude of the Luftwaffe’s best fighters, and fly to Berlin and beyond.
The Spitfire IX was also modified to meet the threat from very high altitude attacks by Junkers Ju 88R and P’s. These German attacks were merely nuisance raids, but in order to meet them the armour and some equipment was stripped from the standard Spitfire IX, which allowed Pilot Officer Prince Emanuel Galitzine to chase a JU88P flown by Feldwebel Horst Götz and Leutnant Erich Sommer to 43,500 feet and damage the bomber before it could escape into cloud. This was the highest altitude air battle of WWII, and ended the high altitude bombing of England.
And finally for this post, in order to meet the threat from V1 flying bombs, (an early cruise missile), Spitfire IX’s were stripped of their camouflage paint, the wings were waxed and polished to a mirror finish, the mirrors were removed, and the armour was taken out. Then, if they were already in the air when the threat was detected, the Spitfire MK IX could catch and destroy the German Terror Weapons. The preferred method of downing a V1 was for the Spitfire to put its wing-tip under the stubby wing of the V1, and then roll sharply. This toppled the flying bomb, destabilised its giro, making it plummet into the ground ~ preferrably in a field somewhere.