The Dornier Do 17 is a twin-engined light bomber designed and produced by the German aircraft manufacturer Dornier Flugzeugwerke. Large numbers were operated by the Luftwaffe throughout the Second World War.
The Do 17 was designed during the early 1930s as a Schnellbomber ("fast bomber") that was intended to use its speed to outrun opposing fighter aircraft. It was a lightly built aircraft, possessing a twin tail, "shoulder wing" and typically powered by a pair of Bramo 323P radial engines. The first prototype made its maiden flight on 23 November 1934, and it entered regular service with the Luftwaffe three years later. Sometimes referred to as the Fliegender Bleistift ("flying pencil") or the Eversharp, the Do 17 was a relatively popular aircraft among its crews due to its handling, especially at low altitude, which made the type harder to hit than other German bombers of the era.
During 1937, the Do 17 made its combat debut during the Spanish Civil War, where it operated as part of the Condor Legion in various roles. Along with the Heinkel He 111, it was the main bomber type of the Luftwaffe at the start of the Second World War. The Do 17 was used extensively throughout the first half of the conflict, seeing action in significant numbers in every major campaign theatre as a front line aircraft. As such, it was deployed during the Polish Campaign, the Norwegian campaign, the Battle of France, the Battle of Britain, and Operation Barbarossa amongst others. Its usage continued unabated up until the end of 1941, when its effectiveness and usage was curtailed by its limited bomb load and range capabilities.
Production of the Do 17 ended in mid-1940 in favour of the newer and more powerful Junkers Ju 88. The successor of the Do 17 was the much more powerful Dornier Do 217, which started to appear in quantity during 1942. The type was not withdrawn at this point; instead, the Do 17 continued to serve with the Luftwaffe during the latter years of the conflict in various secondary roles, including as a glider tug, research, and trainer aircraft. A considerable number were transferred to other Axis-aligned nations, including the Finnish Air Force, Bulgarian Air Force and the Spanish Air Force amongst others. Only a few aircraft are known to have survived the war and none are intact as of the twenty-first century.
Development
In 1932, the Ordnance Department (Heereswaffenamt) issued a specification for the construction of a "freight aircraft for German State Railways", and a "high speed mail plane for Deutsche Luft Hansa". Dornier began work on the design on 1 August 1932.
In April 1934, the Dornier works at Friedrichshafen began project "definition." During this month, the defensive armament was designed and the bomb release mechanism details ironed out. Production of these prototypes began on 20 May 1934 and, on 23 November 1934, the Do 17 V1, with a single fin and powered by a pair of BMW VI 7.3 motors, took off on its maiden flight. Testing was delayed by a series of accidents, with V1 being damaged in landing accidents in February and April 1935. The twin-tailed V2 (powered by low-compression BMW VI 6.3 engines) first flew on 18 May 1935 and was evaluated together with the V1 by the Ministry of Aviation at Rechlin in June. During the tests, the single fin proved to be only marginally stable, resulting in the V1 being modified with a twin tail. The aircraft was destroyed in a crash after an engine failure on 21 December 1935. The V3, also fitted with a twin tail, was originally planned to be powered by Hispano-Suiza 12Ybrs engines, but as these were unavailable, it was fitted with BMW VI 7.3 engines like the V1 and flew on 19 September 1935. The V1 prototype remained the only built machine with the single stabilizer. It has been suggested that it was rejected by Luft Hansa, as the cramped cabin was too uncomfortable for passenger use and the operating costs were too high for a mail plane. According to the story, the three prototypes remained unused in the Dornier factory in Lowental for almost six months, until Flugkapitän Untucht of Luft Hansa came across them. After receiving permission to fly one of the machines, he proceeded to put it through an almost stunt flying routine. After landing, he said that "the machine is as nimble as a fighter, give it more lateral stability and we'll have a high speed bomber!" Untucht's comments prompted Dornier to redesign the tail unit and revived interest in the type.
Dornier was then ordered to produce the V4 prototype. Some sources state this differed from the V3 in that the passenger portholes were removed and the single fin was replaced with two smaller ones. Photographic evidence demonstrates the V3 had twin stabilizers from the start of its construction. The tests of the "twin-tailed" V4, V6 and V7 prototypes were positive and more prototypes like the V8 emerged as the forerunner of the long-range reconnaissance version, while the V9 was tested as a high-speed airliner. The V9 machine was still flying in 1944. As with contemporary German bombers, the crew were concentrated in a compartment.
The cockpit layout consisted of the pilot seat and front gunner in the forward part of the cockpit. The pilot sat on the left side, close up to the Plexiglas windshield. One of the gunners sat on the right seat, which was set further back to provide room for the MG 15 machine gun to be traversed in use. The Do 17 usually carried a crew of four: the pilot, a bombardier and two gunners. The bomb-aimer also manned the MG 15 in the nose glazing and Bola-housed rear lower position. The two gunners operated the forward-firing MG 15 installed in the front windshield, the two MGs located in the side windows (one each side) and the rearward firing weapon. The cockpit offered a bright and panoramic view at high altitude.<!-- the description is described by a series of photographs and captions in Goss--> The standard ammunition load was 3,300 rounds of 7.92 mm ammunition in 44 double-drum magazines.
thumb|left|The Do 17 carried one pilot; to his right sat one of two gunners
The wings were of a broad area and had a span of with a straight leading edge which curved in a near-perfect semicircle into the trailing edge. The positions of the wing roots were offset. The leading edge wing root merged with the top of the fuselage and cockpit. As the wing extended backwards, by roughly two thirds, it declined downwards at a sharp angle so that the trailing edge wing root ended nearly halfway down the side of the fuselage increasing the angle of incidence. This design feature was used on all future Dornier bomber designs, namely the Dornier Do 217. The trailing edge was faired into the round fuselage shape. The engine nacelle was also faired into the flaps. The extreme rear of the nacelle was hollow and allowed the flap with an attached vertical slot to fit into the cavity when deployed.
thumb|upright|[[Luftwaffe radio equipment of World War II#Airborne communications|FuG 10 radio set]]
The fuselage was long. It was thin and narrow, which presented an enemy with a difficult target to hit. The fuselage had twin vertical stabilizers to increase lateral stability. The power plant of the Z-1 was to have been the Daimler-Benz DB 601 but, owing to shortages from priority allocation for Bf 109E and Bf 110 fighter production, it was allocated Bramo 323 A-1 power plants. The Bramos could only reach at . The limited performance of the Bramo 323s ensured the Do 17 could not reach at in level flight when fully loaded. The range of the Do 17Z-1 at ground level was ; this increased to 1,370 km (850 nm) at . This gave an average attack range of . The introduction of the Bramo 323P increased the Z-2 performance slightly in all areas. When fully loaded, the Z-1 weighed .
The Do 17E-1 was equipped with two BMW VI 7.3D inline engines of 750 PS each. The crew numbered three. The radio operator manned the two 7.92 mm MG 15 machine guns within a B-Stand pod in the rear cockpit; they had 750 rounds of ammunition. The bomb bay was divided into two compartments. Each had five bomb racks with individual capacity of . A single ETC 500/IX bomb rack could be mounted externally underneath the aircraft to carry a 500 kg bomb. A Do 17 E-1 with the designation D-AJUN was tested with an unusual configuration, two SC 500 bombs mounted side by side under the fuselage. It showed a notable performance reduction due to the increase in weight and drag, this configuration was not used operationally. The E-1 continued to carry low bomb loads into the Second World War. The performance of the E-1 enabled it to reach a speed of at . Conducting a shallow dive the light frame of the Do 17 could reach . Its maximum ceiling was . Several E-1s were rebuilt as E-2 or E-3, at least three E-2 and one E-3 were used by DVL and Hansa-Luftbild GmbH (Hansa Aerial Photography Ltd) in a secret military reconnaissance role prior to the war.
The Do 17F-1 was a long-range reconnaissance aircraft based on field modified Do 17Es. The Do 17 prototype V8 was used to test the configuration of the F-1 and V11 for the F-2. The defensive armament consisted of a MG 15 in the B- and C-Stand (B-Stand - an upper rear firing position, C-Stand — lower gun emplacement). The fuselage had two cameras along with six ejector tubes for flashlight cartridges. The F-1 saw service until replaced by the Do 17 P in 1938. Only one F-2 was ever built, it was designated D-ACZJ and was used by Zeiss-Jena Company as a factory aircraft.
The Do 17L-0 and Do 17M-0 were developed in parallel as replacements for the earlier E and Fs, the L being the reconnaissance version. Both were designed around the more powerful DB 600A engines, delivering about . Two L and one M versions were built as prototypes, both with another MG 15 in the nose. The first prototype of the revised version, the Do 17M V1 (D-ABVD) was powered by two DB 600s, and demonstrated impressive performance, including a maximum speed of .
At the International Military Aircraft Competition at Zürich, Switzerland, in 1937, the Dornier Do 17M V1 proved a leader in its class and was faster than the fastest foreign fighter, the French Dewoitine D.510.
Radial variants
Despite its success, owing to shortages in the supply of the Daimler-Benz engine, the production Do 17M was fitted with the Bramo 323 engine, with the corresponding reconnaissance aircraft, the Do 17P, being powered by BMW 132Ns to give better range.
The supply of the DB 600 remained extremely limited as production was soon switched over to the fuel-injected DB 601, which was reserved for the Messerschmitt Bf 109 and Messerschmitt Bf 110 fighters. Therefore, production versions of the basic Do 17M model airframe were fitted with the new Bramo 323A-1 Fafnir engines of , which gave reasonable performance and raised the bomb load to . The resulting Do 17 M-1 was produced in small numbers and operated until 1941.
The prototypes for the M-1 series were Do 17M V1 (Werk Nr 691) and Do 17M V2 (Werk Nr 692) which were tested with bomb loads of a medium bomber. The third prototype, Do 17M V3 was evaluated as a fast bomber. The M V1 was fitted with two Daimler Benz DB 601 inline engines while the M V2 and M V3 had the Bramo 323 A and D respectively. The Ministry of Aviation favoured the widespread use of the DB 601, but demand for the DB 601s in fighter aircraft and the lack of production forced the use of the Bramo.
The Do 17 M-1 started its service as a medium bomber and was able to carry of bombs. It was equipped with two air-cooled Bramo 323 A-1 or A-2. The defensive armament consisted of two, and later three, MG 15 machine guns. The first was operated in an A-Stand pod operated by the navigator through the windshield. The position was allocated 370 rounds of ammunition. The rearward firing B-Stand was operated by the radio operator and allocated 750 rounds. The rear position in the lower fuselage was allocated 375 rounds in a C-Stand pod. The Do 17M could carry a bomb load of either 20 SC50 or two SC250 bombs or 10 SC50 and a single SC250 bomb. The speed of the M was superior to that of the E variant. The Do 17M could reach at altitudes of and could achieve a maximum service ceiling of and a range of . The L version would not be able to enter production with the DB 600 owing to its use in the Bf 109, and the Bramo engine was rather thirsty on fuel and left the M models with too short a range for reconnaissance use. BMW 132N radials of 865 PS were selected instead, which had lower fuel consumption for better range. Another two prototypes with DB 600 engines were produced as the Do 17R-0, but did not enter production. During reconnaissance missions the P-1 was armed with four MG 15s in the A, B and C—Stands. One machine gun was located in the rear of the cockpit, another in the lower rear Bola mount, one facing forward through the windscreen and the other in the nose glazing. In earlier variants the B-Stand (the gun position in the upper rear cockpit) was open to the elements, but the P-1 now provided an enclosed bulb-shaped mount protecting the radio operator from the weather.
The P variant had similar features to the Do 17M-1, with added blind flying and camera equipment for reconnaissance work. The Do 17P-1 was powered by two BMW 132N radial engines with a maximum performance of 865 PS ( each. The machine was fitted with several radio variations. The FuG IIIaU radio (Funkgerät), the PeilG V direction finder (PeilG - Peilgerät) and the FuBI 1 radio blind-landing device (FuBI - Funkblindlandegerät). The cameras were controlled remotely by the crew from the cockpit.
The Z-3 formed part of the bomber versions of the Z series, it was, however, also used as a reconnaissance aircraft by the staff flight of the particular unit. The engines and the general equipment were identical to the Z-2 standard; however two cameras — the Rb 50/30 and Rb 20/30 - were incorporated into the crew entry hatch. A handheld camera was issued to the crew to validate the success during bombing missions. Autopilot equipment was added later. The Z-2 and Z-3 were identical visually, and could only be distinguished from each other by the altered crew hatch on the Z-3. Owing to spacing problems because of the added camera equipment, the ammunition supply was reduced from 44 to 42 magazines. The power plant of the Z-3 was upgraded to the Bramo 323P-2. The Bramo P-2 remained the engine of all the remaining Z series variants. Usually the flotation devices took the form of inflatable bags stored in the rear of the engine nacelles and in bulges on either side of the nose, just behind the front glazing.
Later variants of the Z model were developed. The Z-6 was to be a reconnaissance aircraft, although it was only built as a prototype. During the war only a few were converted from existing combat variants. The type was selected for weather check flights. It was identical to the Z-1/Z-2 variants, but offensive armament was omitted and extra fuel cells fitted. This increased the fuel load to 2,890 L (578 imperial gallons). As flights required higher altitude, the oxygen supply was increased from 20 to 24 bottles. For long-range flights over water, the larger dinghy of the Z-5 with its updated emergency escape equipment was mandatory during operations.]]
The Z-8 Geier (Vulture) was not produced. It was intended as a ground attack aircraft and reached the first planning phase but was given up due to lack of performance and protective armour. An increase in armour would have meant a decrease in speed which would have exposed the aircraft further to enemy fire. The Z-9, which was fitted with special bomb release equipment, and delayed release gear for low-level attack missions. Its purpose was to suppress enemy air defences. Therefore, it was designed to fly over anti-aircraft positions and drop Butterfly Bombs, an early form of cluster bomb munitions. This could only be done with air superiority, as the Z-9 was unarmoured. The airframe and equipment was identical to the Z-1/Z-2 version. Only the bomb bay was altered to accommodate 16 bomb-dispenser systems. The maximum weight of the Z-9 was . The design did not reach serial production.
thumb|Dornier Do 17Z-10 night fighter with [[Lichtenstein radar#FuG 202 Lichtenstein B/C|FuG 202 Lichtenstein B/C UHF radar]]
Later, the design was further modified to the Do 17Z-10 Kauz II, the solid nose now containing an infrared searchlight for the Spanner Anlage infrared detection system. The infrared lamp in the nose was used to illuminate the target while the display unit in the windshield made the reflection visible to the pilot. The Z-10 was armed with four 7.92 mm (.312 in) MG 17 machine guns grouped above the IR light and two 20 mm MG FF in the lower nose. A single Kauz II was equipped with and tested the Lichtenstein radar.
Only 10 of these Kauz II designs were converted from Z-series airframes. The Spanner system proved to be essentially useless and many Z-10 were left without any detection system. At least one Z-10, coded CD+PV, was used as a flying test bed to help developing the early low-UHF band B/C version of the Lichtenstein radar system in late 1941–1942.