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.

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.

[10] 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.

Nevertheless, the Gs design features figured and influenced the E-4 which went into production as the aircraft that was envisaged to be the backbone of the Luftwaffe's bomber fleet in the Battle of the Atlantic.

[12] At the end of August 1938 arguments against the floatplane version were made and proposing a land based aircraft to serve as a torpedo bomber, with more potential applications, were accepted.

The four-seat aircraft was adaptable to both land and maritime operations wherein the tactical emphasis was on bombing from a 50-degree dive angle, and it had a maximum speed of 680 kilometres per hour (370 kn).

In contrast with earlier specifications for a modified version of the Do 17M, the proposed Do 217E had a new nose section design in which the A-Stand position was armed with a MG 15 machine gun.

This had a jettison pipe which was attached to the roof of the fuselage and extended to behind the tail wheel..[23] Above the two rear bomb cells in the centre section there was an armoured dinghy stowage place.

[23] The horizontal stabilizer surfaces were conventional, as part of a twin tail empennage with "endplate" vertical fin/rudder units, as on the previous production Do 17 airframes.

[17] The adoption by the Luftwaffe midway through the war, of a general system of unitized powerplant installations for twin and multi-engined combat aircraft incorporating as many of the engine's auxiliary components (radiator and oil cooler, and all fluid and mechanical connections) into a single, easily interchangeable unitized "bolt-on" package, known as the Kraftei (power-egg) concept, was being widely adopted by the time of the Do 217's initial frontline appearance.

[44] The failure of the Heinkel He 111, Dornier Do 17, and Junkers Ju 88 during the Battle of Britain and the Blitz led the OKL to see the Do 217 as the only heavy bomber with the range, bombload and defences for long-range bombing.

The previous lattice air brake was removed; the drag was too much and it bent the fuselage out of shape, making the aircraft unsafe and hastening metal fatigue.

[1] Testing with glide bombs was halted as the electrics were too sensitive to moisture, rockets prone to icing and the radio valves in the control units (in the aircraft) were disrupted by vibrations.

Owing to the problems with the He 177A, Air Inspector General Erhard Milch returned his attention to the Do 217 and demanded a greater number of improved variants for Precision-guided munition (PGM) operations.

E-2s were fitted with a new streamlined "stepless cockpit" following its conceptual debut in January 1938 for the He 111P, as this design philosophy became the standard for almost all German bombers later in World War II, which eliminated the separate windscreen panels for the pilot of earlier versions of the Do 217.

[58] Serious shortages of the BMW 801 led to the cancellation of the K series but tests with BMW 801ML Motoranlage unitized-mount format radial engines, added a supplementary command unit to the usual 801 Kommandogerät engine control unit for each radial, which could engage the booster switch, ignition timing and the weak-rich mixture control automatically, which made the 801L powerplants easy to operate.

[72] In 1941, with Germany under increased night-time attack by RAF Bomber Command and with shortages of the Messerschmitt Bf 110 and the preferred Junkers Ju 88C night fighters, it was decided to supplement the night-fighter force with a version of the Do 217 E, despite its much greater size and 15-ton weight.

[73] This aircraft, the Do 217 J, was fitted with a new "solid" nose, similar to that used by Dornier in night fighter versions of the Do 17 and Do 215, with four forward firing 2 cm MG FF cannon and four 7.92 mm machine guns.

[78] Part of the types performance issues lay with the fact the MG 131 defensive guns and bomb release mechanisms had remained, and been built into the J-1 to allow for its use as a bomber.

Schoenert suggested to his Commanding officer, in July 1942, that trials be made of weapons slanting upwards at an angle of 70° (later known as Schräge Musik) in the fuselage in the hope of increasing the efficiency of his Do 217.

Unlike the B-17 Flying Fortress or B-24 Liberator, the British bombers did not have a ventrally-located Ball turret, and the new Dornier design attempted to take advantage.

Other tactical improvements involved fitting a semi-rigid brake parachute in October 1942, allowing the Dornier to adjust to the speed of the bomber before firing on its target.

The no longer needed bomb release gear remained, bringing the aircraft up to 15,000 kilograms (33,000 lb) on take-off, so it was barely able to reach 7,400 metres (24,300 ft).

[69] Some modified with dorsal and ventral guns replaced by wooden fairings as Do 217 N-1/U1, conversion with Schräge Musik arrangement of four upward-firing 20 mm MG 151s as Do 217 N-1/U3.

Brown made a straight dive to 700 km/h (430 mph), the maximum permitted below 3,000 m (9,800 ft) in order to get a feel for the controls, which began to stiffen considerably.

[102][103] Deliveries of the Do 217E started late in 1940, with some aircraft joining another reconnaissance unit, 2 Staffel of Fernaufklärungsgruppe 11, which was also involved in spyflights over the Soviet Union from bases in Romania.

It had suffered serious losses of trained personnel during operations during 1942, with the number of combat ready crews in KG 2 falling from 88 at the start of the year to 23 by September.

[115] This attack lead to a temporary withdrawal of Royal Navy surface ships from the Bay of Biscay until the guided weapon equipped aircraft were transferred to the Mediterranean following the allied landings at Salerno.

[117][118] As American forces broke out of the bridgehead at the end of July, III/KG 100 sent its remaining Do 217s to carry out attacks on bridges over the Rivers Sée and Sélune with Hs 293 missiles.

[115] The Dorniers of KG 100 continued to be deployed against convoys in the Mediterranean, but by the time of the Anzio landings in January 1944, heavy allied fighter cover and jamming reduced the effectiveness of the attacks, although Hs 293 missiles sank the cruiser HMS Spartan and several destroyers and merchant ships.