This piston-engine fighter aircraft is probably the most powerful German design of its type and represented the pinnacle – as well as the end - of this era of military aircraft design. However, it was not the result of the initiative of Professor Claude Dornier – as often asserted – but came about through one of his sons, Peter Dornier. The design was based on the concept of equipping an aircraft with a nose engine and a rear engine plus the appropriate propeller. The aim was to transfer the engine output of the rear engine with an extension shaft, while the cockpit was to be configured between the two engines. This configuration achieved a powerful twin-engine aircraft with the air resistance of a single-engine design. In 1937, a fighter aircraft with an appropriately modular design was developed in the project P.59 and protected under patent law. Three years later Dornier successfully tested his engine concept in practice using the Göppingen Gö 9 test-support aircraft. Nevertheless, the authorities only became interested in his concept when they put out a tender for a fast bomber. The P.231, a single-seater low-wing aircraft with a cruciform tail unit, nose and rear engine and tricycle landing gear, was intended to achieve a speed of more than 750 km/h. Although the P.231 won the tender for the fast bomber, no priority was given to realizing the aircraft.
Work started on converting the P.231 to a fighter aircraft when Luftwaffe commanders requested a new high-speed fighter plane with a piston engine at the end of 1942. The aim was to implement this project as quickly as possible to provide a stop gap until reliable jet engines were introduced. Construction of the first prototypes was approved in January 1943. The technical features of the aircraft included installation of a pneumatically operated ejector seat, which was intended to provide pilots with a safe emergency exit, together with explosive charges for blowing off the upper vertical tail plane and the rear propeller in case of an emergency. Daimler Benz DB 603 E engines were projected as power units – if available. Alternatively, the DB 603 A or the Jumo 213 was to be installed. The airframe also offered adequate opportunities to mount a wide range of heavy weapons, especially since a dedicated bomb bay was to be provided.
The first pre-production model for the aircraft now designated as the Do 335 took off on its first flight on 26 October 1943. Although the aircraft was not easy to fly, it was astonishingly manoeuvrable. Pilots also quickly attained speeds of 770 km/h. Another eight test aircraft with different engines followed until the end of June 1944. Ten A-0 pre-production aircraft were then produced. However, since the Do 335 had been in direct competition with the generally favoured jet fighters for a long time, preparations for volume production only proceeded very slowly. Even an experimental command unit 335 created especially for this aircraft was unable to change matters.
No less than 23 different sub-versions of the aircraft were requested and planned for a wide range of different operational aims with continually changing priority and urgency. This was also one of the reasons for the ongoing delay in setting up large-scale volume production. Apart from single-seater reconnaissance aircraft, high-altitude fighters, fast bombers and destroyers in the versions A-2 to A-5 and A-7 to A-9, as well as B-0 to B-4, planners also envisaged the twin-seater night bomber or trainer variants A-6, A-10 to A-13, B-5 to B-8 and B-12. There were also numerous projects for advanced development of the aircraft through to a jet-powered variant or for example the twin-fuselage Do 635, which was intended as a strategic long-distance reconnaissance aircraft and was to be produced in conjunction with Junkers and Heinkel.
The first production aircraft of the Do 335 only left the final assembly halls in Oberpfaffenhofen starting in November 1944. However, these were only individual examples of the A-1 version and the twin-seater A-11 or A-12. The aircraft were never deployed operationally, although the Americans, Britons and French showed considerable interest in testing aircraft that had been captured at the end of the war. Although there were no more moves towards future fighter aircraft planning, the performance of the Do 335 left a strong impression. Only one of the pre-production aircraft of the type A-0 captured by the Americans escaped being scrapped subsequently. It underwent expensive restoration at Dornier in Oberpfaffenhofen in 1974/75 and is now exhibited in Washington.
