WW2 GERMAN LUFTWAFFE DORNIER Do217 BOMBER NIGHTFIGHTER ANTI-SHIP MISSILE CARRIER

MNOGOTSELEVOY BOMBARDIROVSCHIK SOFTBOUND BOOK with RUSSIAN TEXT

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Additional Information from Internet Encyclopedia

The Dornier Do 217 was a bomber used by the German Luftwaffe during World War II as a more powerful development of the Dornier Do 17, known as the Fliegender Bleistift (German: "flying pencil"). Designed in 1937 and 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's 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 capacity and had 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 operated as a strategic bomber, torpedo bomber and reconnaissance aircraft. It also performed 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. It was in the Mediterranean that the Do 217 became the first aircraft in military aviation history to deploy a form of precision-guided munition in combat, in the form of the Fritz-X radio-guided, free-fall bomb, which led to the sinking of the Italian battleship Roma in 1943. 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.3 In February 1938 the Reichsluftfahrtministerium (RLM – Air Ministry) authorized a testing program.4 Dornier worked on a version of the Do 17M with the all round vision cockpit of the Do 17Z and a fuselage having 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.5 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 slightly larger than the Dornier Do 17 by one metre. Its overall span was now 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 had 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 of the power plants was selected, the RLM expected the aircraft to achieve a maximum speed of 520 kilometres per hour (280 kn) and have a weight of 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 with 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 structurally stronger.

The RLM also had other requirements for Dornier to fill. Since 1933 Nazi Germany's 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 that 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).8 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 Dornier floatplane. For hitting targets in the air and sea surface, four machine guns 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 machine guns (200 rounds of ammunition) as part of the Dornier Do P.85 project.9 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 115.9 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 pay load 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, like the Ju 88. 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 to supply the power plant were located in the wing and fuselage which had a capacity for 2,000 litres (440 imp gal) of aviation 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 to be 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 1938.10 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.10 Although specifically ordered to cease development of the naval version of the Do 217,11 Dornier unofficially pursued the project and produced the Do 217W V1 and W V2 prototypes.12

By the summer, 1940 the Luftwaffe had been using the Dornier Do 18, Heinkel He 115, Heinkel He 59, Heinkel He 111 and Junkers Ju 88 in maritime operations in the Baltic. At this point, the Ju 88 and He 111 equipped units were ordered to cease providing maritime support en masse. Instead, the Luftwaffe returned to the idea of the Do 217 and its floatplane version as a specialized naval attack aircraft. At the same time more plans were in place to produce extremely long-range aircraft (probably for operations deep in the Soviet Union). It is possible that the data sheet which Dornier gave the designation Do 217G was a part of that project. Unlike the Sea Stuka, a floatplane, the G was to carry an MG 151 mounted in the nose and three MG 15s fitted for defence. The G was expected to reach 14,900 kilograms (32,800 lb). It was still designed for a crew of four and equipped with sprung floats which would allow the aircraft to land in rough open seas. The G could also carry the entire variation of the E-1 bomb load it could carry a load twice that of the Do P.85 aircraft. However, the Do 217 E-1s performance was favoured. 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.

The Do 217 usually carried a crew of four. Included were a pilot, an observer/bomb aimer/forward gunner, dorsal gunner/radio operator and a flight engineer/ventral gunner. As with the Dornier Do 17, the crew were positioned in the cockpit cabin forward of the engines and leading edge. The pilot sat on the port side, with a spectacle-type control column mounted on a swinging arm centered in the instrument panel. The entire arm could be swung 180deg to starboard, placing the yoke in front of the bombardier, in case of emergencies. In the later Do 217K with stepless windscreen, the center pivot was mounted on a rocking control arm or pedestal, rather than a sliding piston, since the instrument panel itself was eliminated (replaced with smaller panels holding the gauges, hung from the edge of the fueslage wall and from the glazing frames above the yoke, respectively.)16 The bomb aimer sat on his immediate right, slightly below and behind. In combat he could move forward into the nose and operate the bomb release gear or aim the forward machine gun (or 20 mm cannon). On the right side of the nose, the bomb aimer's window penetrates the cockpit and is visible as a bulge on the exterior. Back-to-back with the bombardier’s seat, the flight engineer/ventral gunner sat on the port side, his seat facing to the rear. The seat of the ventral gunner/flight engineer was next to the radio operator facing forward, behind the bomb aimer. During operations the ventral gunner/engineer would lie on his stomach facing aft, his post as a gunner taking immediate and first priority.16 The radio-operator/dorsal gunner sat in a pivoting seat in the extreme rear, above the ventral gun position. His head was inside the B-Stand gun position, and the instruments mounted in a semi-circle around his torso level. The pilot had a curved shield of Armour plating, 8.5 mm thick, placed behind his seat. His seat had a further 5mm (​1⁄4 in) of armour and another 5mm (​1⁄4 in) plate above his head, installed in the top of the cockpit roof.26 The dorsal gunner was also protected by armour plating.27 The Funkgerät or FuG radio communication device compartments were located in the extreme rear of the cockpit, near the leading edge. The automatic pilot panel was located next the FuG boxes. In the right-rear of the cockpit the piping that was also attached to the de-icing ducts in wings also entered the cockpit, as part of a single heating system to emit warm air to heat the cabin if needed.22 The FuG X, 16, navigational direction finder PeilG V direction finder (PeilG – Peilgerät) and the FuG 25 IFF and FuBI 2 blind landing devices were used in the E-2.

The defensive armament consisted of an A-Stand (forward firing machine gun position) in the nose with a MG 15 machine gun. In the C-Stand (lower rear gun emplacement) at the rear end of the undernose Bola gondola – a standard feature on many German twin-engined bombers – and a B-Stand position (rear-upper gun post) at the rear of the cockpit glazing, the crew were provided with MG 15 (E-1) or MG 131 machine guns (E-2). In the side of the cockpit, two MG 15s were mounted (one on each side) on bearings. As well as the manual machine gun positions, the E-2 was equipped with a Drehlafette DL 131 rotating turret armed with 13 mm machine gun.29 In some instances, a moveable 20 mm cannon was fitted in the nose and a fixed 15 mm weapon was installed in the floor of the nose. The weapons could be controlled by the pilot, via a firing button located on the yoke. To assist in acquiring his target, a Revi C12/C was installed in the cockpit.

The maximum permissible bomb load of the E-series without sacrificing fuel load was 3,500 kilograms (7,700 lb) of bombs of which a maximum of 3,000 kg could be carried internally.31 To have the maximum load of 4,000 kg, part of the 1,050 litres (230 imp gal) fuselage fuel tank had to be sacrificed. If long distance operations had to be flown, drop tanks could be fitted under the wings, which affected speed.32 Beside the bomb load a LT F5 Torpedo could be carried in its long bomb bay, as well as three aerial mines (the E-1 did not carry the mine load of the E-2).

To replace the Do 217, the RLM planned for the He 177 A-3 and A-5 to be the long-range carrier aircraft for missiles, owing to the lack of BMW engines to power the Dornier but problems with the engine reliability of the He 177A led to the failure of the plan. The Battle of Stalingrad used up more and more aircrew which prevented them retraining on the Do 217 for glide bomb operations. 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.51

In early 1942, tests on a new and improved, completely glazed cockpit for the Do 217 series had been underway at the Hamburger Schiffbauanstalt (Hamburg Shipbuilding Institute). 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. The lower nose of the K-version also retained the Bola inverted-casemate gondola for a rearwards-aimed ventral defensive armament emplacement, with its forward end fully incorporated with the new nose glazing design. The testing for this new well-framed cockpit glazing format for the later models of the Do 217, was carried out at the Shipbuilding Institute in Hamburg. The design of the cockpit was put to the test using water pressure to simulate a speed of 700 km/h. Only a few of the glass panels failed, caused by inadequate mounting. The cabin design passed the tests easily.52 Initial flights took place on 31 March 1942 after teething problems had been resolved. The Do 217 K V1 flew with BMW 801A-1s from Löwenthal and Erprobungsstelle Rechlin. This was followed by the ten-airframe pre-production batch, Do 217 K-01 to K-010. Mass production of the Do 217 K-1 began at the Dornier factory at Wismar.

The Do 217 K-1 was a night bomber version with the 1560 PS BMW 801L engine.57 It carried the same crew of four in the "stepless cockpit" crew compartment with a revised defensive armament of a twin-barreled 7.92 mm MG 81Z machine gun in the nose, two single MG 81s or twin-barrelled MG 81Z in beam positions, a MG 131 in the B stand position dorsal turret, the DL 131/1C, and another in a ventral position inserted in a Walzenlafette WL 131/1 cylindrical carriage at the rear of its Bola gondola.58 220 were built.2 It had an average flying weight of 12,700 kg, this aircraft achieved speeds of 520 km/h at 5,200 m.

The K-1 was equipped with GM 1 nitrous oxide boost, which increased the K-1s maximum speed by 84 km/h at 8,000 m at a rate of 100 g/s. With 50 g/s the aircraft's operational ceiling could be extended from 8,400 to 9,800 metres. Failure rates of the GM 1 were very high and attention was shifting to other Do 217 variants and the use of GM 1 soon stopped.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. Oil pressures also triggered operation of the VDM propellers, which on the K-1 subtype were 3.9 m in diameter. A smaller, 3.8 meter diameter wood-bladed propeller could be used as an alternative, though with a slight loss of speed. The standard 2,165-litre fuel tank could be supplemented by two fuselage tanks with 700-litre capacity or with either the standardized Luftwaffe 300 litre drop tank used on many German front-line military aircraft or fin-stabilized 900 litre drop tank as the Bf 110D used. An all-up-weight of 15 to 16.5 tonnes could be expected. The K-1 would need some 850 to 1,110 m to get airborne. Taking off from a grass strip, an altitude of 20 m was reached after 1,500 m and from a concrete runway it was 1,300. With two auxiliary tanks its speed dropped by 4.5 percent, and with bombs, by 6 percent. Flame-damper equipment also caused serious speed reductions; 7 percent in level flight and 9 percent when at operational ceiling.

The next variant, the Do 217 K-2, was a specialised anti-shipping version based on the K-1, the Do 217 K-2 was intended to carry the Fritz X guided bomb, being fitted with pylon-faired hardpoints to allow carriage of two Fritz Xs inboard of the engines and the appropriate Kehl guidance system transmitter emplacement. It had longer-span wings (24.8 m (81 ft ​4 1⁄2 in) compared with 19 m (62 ft 4 in) for the K-1) to give better high-altitude performance when carrying the heavy Fritz-X bombs. 50 were converted from K-1 airframes.2 The wing area was expanded by a total of 67 m2, but most of the K-2s internal equipment was the same as the K-1.60 The increase in area was to increase high-altitude performance.58 Some of the K-2s had a rigid tail MG 81Z which was not especially effective.61 It was loaded with 350 rounds and controlled by the use of a rear-facing telescope mounted in the forward section of the canopy left of the pilot. Either the gunners or pilot could fire the weapon, which could be jettisoned in case of an emergency to reduce weight.

As the BMW 801 radial engine used by the Do 217K was in great demand for the Fw 190 fighter, the Do 217M, a version powered by Kraftei-unitized installation versions of the largest displacement inverted V12 then in service, the 44.5 litre displacement Daimler-Benz DB 603 liquid-cooled inverted V12 engine, was developed in parallel with the 217K. It shared the new forward fuselage of the 217K, with the first prototype flying on 16 June 1942.6364 According to RLM plans, production of the M model, which was powered by DB 603 A-1s was due to commence with two aircraft in May 1942 and 10 M-1s in the summer. By March 1943 a production target of 42 aircraft per month was to be achieved. The DB 603 A-3 was chosen as the increased performance handed the aircraft improved characteristics. However, it had not been fully tested and a number of technical problems arose. A Do 217H (a glider-bomber for land operations with E-2 airframe) would be used for endurance testing. This would provide useful testing evaluations for the M-1.

The M-1 night bomber version, equivalent to Do 217 K-1 but with DB603A engines, carried similar armament and bomb load to K-1.6869 Daimler-Benz DB 601s were also used on some variants to keep the airframes in service (the shortage of powerplants made this difficult).70 Mostly though, DB603A-1 engines were used on the M-1, its only major difference with the K series. The M-1/Umrüst-Bausätze 1 (abbreviated "/U1") incorporated the M defensive armament and the lattice air brake of the E-2. The MG 81Z and 131 were to be replaced by the MG 151 in the A-stand position. Problems with the air brakes prevented serial conversions. By November 1943 the M-1/U1 had matured into a night bomber with anti-glare protection in the cabin. The machine was equipped with a MG 131 in the nose, two MG 81Js in the cabin windows and two MG 131s in the B and C stand.67 Some M-1/U2s were fitted for deployment of German PGM guided ordnance with the required FuG 203d Kehl IV guidance transmitter, and rear-looking FuG 216 Neptun R radar equipment.71 438 M-1 were built by Dornier in Munich and Wismar.

In 1941, with Germany under increased night-time attack by the bombers of 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 217E, despite its much greater size and 15-ton weight.72 This aircraft, the Do 217J, 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.5563 By October 1940, the production of heavy night fighters, and night fighters such as the Do 217 and Ju 88, had been discussed comprehensively and by 5 November 1941 these discussions had been concluded. On 23 November the Technische Amt (T.A) had ordered the Dornier bomber fleet to be withdrawn in accordance with a decision made earlier that year on 23 May. Dornier designated the subject of their new project the "Do 217Z", later renamed the Do 217J.

The Japanese Imperial Navy and Japanese Army Air Force had also taken an interest in license building the type in the summer 1942, demonstrating the type's potential. The Luftwaffe, however, had no intention of delivering the Do 217 to Japan, and none were ever exported.73 Dornier encountered many problems in procuring the BMW 801 engines required for the night fighter versions. Junkers had also struggled with BMW deliveries, its Ju 88C variants were to be powered by the BMW as the initial Jumo 211B/F engine plan had been abandoned.73 The Do 217s competitor, the Ju 88C, had only four fixed guns, whereas the Dornier could hold eight. In most cases, the Ju 88C carried only one 2 cm MG FF and three 7.92 mm MG 17s.73

In January 1941 Junkers concentrated on the C variant designs. It planned on producing 60 C-4s and 374 C-6s powered by Jumo 211s. It later transpired to Dornier that Junkers also wanted the BMW 801 to power the C-6. The power plants would also be supplemented with GM-1 nitrous oxide injection engine performance boosters for greater performance or alternatively, using the new, more powerful Jumo 213. The Ju 88s weaponry was improved by the addition of one or two MG FFs in the fuselage. Both the Do 217 and Ju 88 used the FuG 202 Lichtenstein B/C sets, but later Ju 88s were given FuG 212 Lichtenstein C-1s and later FuG 220s. The equipment of the Dornier did not change. Against this competition Dornier needed to improve the types abilities as a night fighter.73 The first problem Dornier attempted to overcome was long and short range capabilities. A modified E-1, (Wrk Nr. 42) was used to test the equipment for the forthcoming Do 217J. During testing the characteristics of the various types fire extinguisher hardware were carried out. Performance trials were carried out in January 1942 using a E-2, Wrk Nr. 1122 which was put through its paces at the Löwenthal testing facility.73

Dornier intended the prototype to ready by February 1942. The machine, Wrk Nr. 1134, was a modified E-2 and equipped with FuG 202 and a Spanner-Anlage Infrared gun sight. These systems enabled the Dornier to detect the heat signature of enemy aircraft. Heat seeking detection at limited range making the Dornier a good proposition for the Defence of the Reich campaign. Testing was set back as the prototype crashed owing to engine failure. The continuing slow development of the IR equipment precluded its use in the J-1. Work on the IR program was sped up until late 1943. Modified IR equipment appeared in 1945 and was installed in the Ju 88 G-6.74

Delays of BMW 801 engine deliveries forced the project to be temporarily abandoned. In November 1941 the directive for the design team had been a J-1 with a Spanner IR system, and a J-2 with Lichtenstein radar. In 1942 the directive changed slightly, and the J-2 was to be fitted with AI radar. Specifically, the Dornier was to be armed with four MG FF fuselage mounted cannon and machine guns for bomber assault, and one MG 131 each in the B-Stand and C-Stand positions for defence from RAF night fighters. Curiously, the night fighter version was ordered to be able to carry eight 50 kg bombs75 so the type could act as a night fighter and intruder over enemy territory.76

The electronic equipment to be installed was listed as the FuG X, 16, 25 Peil G V air-to-ground communications and blind landing devices. The FuB1.1 was also listed as a potential piece, and if possible a FuG 101 radio equipment was to be fitted as standard. It was intended to equip J-1 with the Lichtenstein FuG 202, which had an effective range of 4,000 metre, with three tubes. The weight of the equipment would reduce the performance of the J-1 by 30 – 40 km/h so in January 1942, Dornier opted to install the IR spanner equipment instead of the Lichtensten.75 A rear braking system had also been in the original plan, but it was deemed unnecessary.75 The design was declared ready on 5 January 1942 and first flew later that month. The prototype was delivered to the Tarnewitz test facility where gunnery trials took place with MG FF and MG 17 weapons. Satisfied with the performance, series production began in March 1942.

The operational Dornier night fighter, redesignated J-1, before entering operations was powered by BMW 801L engines. It was fitted with a revised crew compartment housing a crew of three, with a solid nose housing four fixed 7.92 mm MG 17 machine guns, with four 20 mm MG FF/M cannon in the forward part of the ventral gondola. It retained the MG 131s in a dorsal turret and ventral position of the bomber, and could carry eight 50 kilograms (110 lb) bombs in the rear bomb-bay, with a fuel tank in the forward bomb-bay.7879

Production had commenced in March 1942, during which eight J-1s were built. In April, 13 followed and 55 were built in May. Despite this start production declined in June and this trend continued until November 1942, when only four were built. Dornier had been ordered to withdraw Dornier airframes for unspecified reasons. Owing to this, by 31 December 1942, only 130 J-1s had been completed.2 Dornier kept a production run of 19 aircraft for evaluating equipment. These were to be used when Josef Kammhuber, General of the Night fighters demanded the J-1 to have a modified fuselages made available for upward firing cannon installed within the dorsal areas of the fuselage, above the wing roots. This armament configuration was called Schräge Musik ("slanted" or "oblique" Music). A prototype was given four MG 151s in place of its MG FFs and named J-1/U1.77 The prototype was modified in September 1942 and sent to the Tarnwitz Experimental Establishment on 14 October for tests on gunnery performance. The guns delivered 125,000 rounds during tests without problems. The concept was available for adoption, although Dornier had some reservations about the slow firing pattern of the MG 151/20.

The Dornier appeared to be a very effective night fighter with significant hitting power. However it attracted strong criticism from the Luftwaffe. After the first J-1 was delivered to 4./Nachtjagdgeschwader 1, in March 1942, the crew complained it was too heavy, and criticised its take off and landing characteristics. The pilot complained it had "too little performance reserve". The aircraft's high service loading and its poor manoeuvrability in aerial combat did not enhance its performance reputation.77 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. With eight machine guns mounted in the fuselage and the supporting ammunition, the weight was increased and outweighed the Do 217E by 750 kg.

The end of the J series did not mean the end of the Dornier night fighter. One of the few German fighter pilots to side with the type against its critics was Hauptmann Rudolf Schoenert of III./Nachtjagdgeschwader 3. 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. This entailed mounting four to six MG 151/20 guns in the centre of the fuselage. At Technisches Amt, two Do 217s, one with four and the other with six MG/151/20 cannon were ready for inspection on 5 August 1942 and testing in September.82 The idea of the upward firing cannon had originally come from an engineer, Dr. Poppendieck, in June 1942.82 Nevertheless, Schoenert built on it, and with the introduction of the IR spanner and headlight, the bomber could approach from below a British bomber and avoid exposure to its powerful powered turrets guarding its tail, nose and upper fuselage by attacking from behind or head-on. Unlike the B-17 Flying Fortress, the British bombers did not have a Ball turret, and the new Dornier design attempted to take advantage.82 It was decided, due to cost, to limit the upward-firing armament to four guns. 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 prototypes J-1/U2 and J-1/U4 were tested under these conditions.

These designs were to be carried forward into the new variant, the Dornier Do 217N. The BMW 801 that powered the Do 217J proved underpowered, so a night-fighter using the more powerful DB 603 A-183 engines was produced, with the first prototype flying on 31 July 1942.80 While it had much improved performance, it was still unpopular due to its poor agility and climb rate,63 and was prone to engine problems.81 Ten pre-production series N variants were designated as test beds. Trials began in the summer of 1942. On 16 August the second prototype Do 217, N V2, entered trials,. The N V1 and N V2 were the main testbeds, and the DB 603 A-1s they were powered by were tested at high altitude. On 11 October 1942 the N V1 crashed after stalling with its landing gear down and crashing into Müritz Lake, killing the crew. On 21 December 1942, 100-hour engine endurance trials began at Rechlin with the DB engines. The pistons became useless after 91 hours. Testing of DB 603 A-2 inline engines was carried out between 28 April and 8 May 1943, but the programme was beset by continual breakdowns and the project was abandoned. There was no further record of the N variant prototypes after 20 June 1943.83

In April 1943, the four MG FF guns had started but were not completed until the late summer. The third prototype, N-1/U was fitted with MG 151/20 and unspecified aerodynamic refinements. The machine was used in high-altitude de-icing tests, and the aircraft was tested with Lichtenstein BCR and Bernhardine radar. In August ten of these aircraft were constructed, and between 27 and 31 August, they were fitted with their Schräge Musik at Tarnewitz and Wismar Testing Facilities. The tenth N variant, designated N-0, underwent radio trials. The machine was tested with the Peil G VI/APZ 6, a later and more sophisticated variant automatic direction-finding equipment. On 2 December further tactical trials were carried out with infrared target-illuminating equipment. These trials were carried out with DB 601 powered J-1.