Dornier Do 217

The Dornier Do 217 was a bomber used by the German Luftwaffe during World War II. It was a more powerful development of the Dornier Do 17, known as the Fliegender Bleistift (German: "flying pencil"). Designed in 1937–1938 as a heavy bomber but not meant to be capable of the longer-range missions envisioned for the larger Heinkel He 177, the Do 217 design was refined during 1939 and production began in late 1940. It entered service in early 1941 and by the beginning of 1942 was available in significant numbers.

The Dornier Do 217 had a much larger bomb load and a much greater range than the Do 17. In later variants, dive bombing and maritime strike capabilities using glide bombs were experimented with, considerable success being achieved. Early Do 217 variants were more powerful than the contemporary Heinkel He 111 and Junkers Ju 88, having a greater speed, range and bomb load. Owing to this it was called a heavy bomber rather than a medium bomber. The Do 217 served on all fronts in all roles. On the Eastern Front and Western Front it was used as a strategic bomber, torpedo bomber and reconnaissance aircraft. It was also used for tactical operations, either direct ground assault or anti-shipping strikes during the Battle of the Atlantic and Battle of Normandy. The Do 217 was also converted to become a night fighter and saw considerable action in the Defence of the Reich campaign until late in the war.

The type also served in anti-shipping units in the Mediterranean, attacking Allied convoys and naval units during the Battle of the Mediterranean. In 1943, the Do 217 was the first aircraft to deploy precision-guided munitions in combat, when Fritz X radio-guided bombs sank the Italian battleship Roma in the Mediterranean. After the end of the war, at least one Dornier Do 217 continued in military operational service with the Swiss Air Force until 1946.

At the beginning of 1938, Dornier issued manufacturing specification No. 1323, recognising the need for a twin-engine bomber or long-range reconnaissance aircraft powered by Daimler-Benz DB 601B engines. In February 1938 the Reichsluftfahrtministerium (RLM/German Aviation Ministry) authorized a testing program. Dornier worked on a version of the Do 17M with the all round vision cockpit of the Do 17Z and a fuselage with a large bomb bay capable of holding a maximum of two 500 kilograms (1,100 lb) and ten 50 kilograms (110 lb) bombs. For reconnaissance an Rb 50/30 movie camera was fitted ahead of the front spar of the wing, and an Rb 20/30 was mounted in the second bomb bay. Jettisonable fuel tanks were carried in the forward bomb bay. For smoke-laying, the aircraft could be fitted with two Type S200 smoke generators. Dornier also envisaged the Do 217 as a naval dive bomber, in which case it was to be fitted with twin floats. In April and May 1938, the Do 217 WV1 and WV2 prototypes were produced.

The wing span was to be one metre greater than that of the Dornier Do 17, giving an overall span of 19 metres (62 ft 4 in). Under the wing a retractable diving air brake was to be installed. To power the aircraft the Dornier office at Manzell favoured two DB 601B engines, which could generate 1175 PS (1159 hp, 864 kW) for take off. The Jumo 211, Bramo 329 and BMW 139 (forerunner to the BMW 801) were also considered. Whichever power plant was selected, the RLM expected the aircraft to have a maximum speed of 520 kilometres per hour (280 kn) and weigh 10,200 kilograms (22,500 lb) fully loaded. On 5 June 1938 Dornier's overview of its design submitted to the Technical Bureau (Technisches Amt) highlighted some structural differences from the Do 17. In particular, the proposed increase in the bomb load to 1,500 kilograms (3,300 lb) had to have been a vital factor in the design's acceptance. The fuselage was to be not only bigger but also stronger.

The RLM also had other requirements for Dornier to satisfy. Since 1933 the Kriegsmarine had pressed for the formation of a Naval Air Arm. In January 1938 the Naval Air Arm Inspectorate of the Luftwaffe presented its requirements for a multi-role twin-engined all-metal aircraft which could also conduct maritime operations. On 5 February 1938 it was agreed with the General Staff. The ineffectiveness of horizontal bombing of ship targets had already been noted. At the Erprobungsstelle Travemünde military aviation test centre at Greifswald, training units together with a few naval air units practiced bombing the ship Zähringen with concrete bombs. The results were a two percent hit rate. Junkers Ju 87 dive bombers repeated the assault with a 40% hit rate. The superior accuracy of dive bombing was clearly demonstrated. The Luftwaffe also wanted a machine that could operate as a fighter aircraft to combat enemy aircraft. Essentially they wanted a "sea Stuka" (Junkers Ju 87). The aircraft was to have floats and a range of 1,500 kilometres (930 mi) and a maximum speed of 400 kilometres per hour (220 kn).

Dornier set about designing a floatplane. For hitting targets in the air and sea surface, four automatic weapons would be fitted in the nose. The armament would consist of two MG 17 machine guns (500 rounds of ammunition each) and two MG 204 (aka Lb 204) 20mm autocannon (200 rounds of ammunition) as part of the Dornier Do P.85 project (in German sources these were all classified as "machine guns", since the Luftwaffe considered anything 20mm or lower a "machine gun", rather than a cannon like Western nations, hence the "MG" designation). Heavy weapons consisted of one 500 kg or two 250 kg bombs for assaulting enemy warships. Dornier faced competition from Heinkel and Junkers who were developing the Junkers Ju 88 and Heinkel He 115. Instead of MG 204s, MG 151 or MG FF was installed instead. Defensive armament was to consist of MG 15s to cover the aft approach. In addition the payload could be modified to one 500 kilograms (1,100 lb) and eight 50 kilograms (110 lb) bombs or even two SC 500 bombs. The floats had a volume of 8,100 litres (1,800 imp gal) and were broken into compartments for safety reasons. Each float was to contain a fuel tank with a capacity of 500 litres (110 imp gal). The tail was to consist of the same twin stabilizer configuration as the Do 217, although a single fin was planned.

For dive bombing capability a dive brake was installed underneath the wing. The power plants were to reflect the speed requirements. It was envisaged as having two DB 601G engines, generating 1,300 horsepower (970 kW), or two Jumo 211s. The fuel tanks were located in the wing and fuselage which had a capacity for 2,000 litres (440 imp gal) of fuel and 190 litres (42 imp gal) of oil. At full weight the Dornier would reach 360 kilometres per hour (190 kn) and its effective range was expected to be 1,880 kilometres (1,170 mi). Its optimum range at an average cruising speed of 270 kilometres per hour (150 kn) at an altitude of 4,000 metres (13,000 ft), was 2,800 kilometres (1,700 mi). The specifications were dated 8 March 1938. The Do 217 lost out in the naval aircraft race to the Ju 88 and Blohm & Voss Ha 140, as the Luftwaffe favoured these designs owing to the Do 217 failing to live up to the specifications given. Although specifically ordered to cease development of the naval version of the Do 217, Dornier unofficially pursued the project and produced the Do 217W V1 and W V2 prototypes.