The arrival of the Spitfire IX in Fighter Command and its threat to combat domination by the Fw 190A led to the development of the Fw 190B series with GM-1 power-boosted BMW 801D-2 engine and pressure cabin, but trouble with the latter led to the abandonment of this version after only a few prototypes had been produced. The Fw 190C series, of which five prototypes were completed with DB603 inline engines, annular radiators, Hirth 9-2281 superchargers and four-bladed propellers, was also abandoned early in 1944.
The Fw 190D, with 1,770hp Junkers Jumo 213A-1 engine and annular radiator in a much-lengthened nose (necessitating increased fin and rudder area), proved very successful after it had first flown at Langenhagen in May 1944. The first production Fw 190D-9s (so termed because they followed the Fw 190A-8s at the factories, and widely known as ‘Dora-Nines’ in the Luftwaffe) joined IIL/JG 54 in September 1944 to defend the jet base of Kommando Nowotny. Among the sub-variants of the Fw 190D series was the Fw 190D-10 with a single 30-mm MK 108 cannon located between the engine cylinder banks and firing through the propeller hub. The Fw 190D-12/R21, a ground-attack version of the hub-gunned Fw190D-10 and power-boosted with MW50 water-methanol injection, was almost certainly the fastest of all Fw 190s with a top speed of 730 km/h at 11000 m. Dora equipped most of the Luftwaffe’s fighter units during the last fateful months of the Third Reich, but in combat with the Allies – particularly their P-51s and Spitfire XIVs – they were frequently overwhelmed. The Luftwaffe’s problems centred on a shortage of fuel, which allowed only small formations of fighters, and of battle-hardened veteran pilots. For instance, when JG 6 (commanded by Major Gerhard Barkhom, the German pilot who had a combat record of 301 air victories) in April 1945 took delivery of 150 brand-new Dora-Nines, it could only fly patrols by four aircraft at a time against massed wings of Allied fighters.
David Donald: Fighters of World War II