German twin engine multirole combat aircraft
The Junkers Ju 88 is a twin-engined multirole combat aircraft designed and produced by the German aircraft manufacturer Junkers Aircraft and Motor Works. It was used extensively during the Second World War by the "Luftwaffe" and became one of the most versatile combat aircraft of the conflict.
The Ju 88 originated from a "Reichsluftfahrtministerium" (RLM) requirement issued in 1934 for a new multipurpose aircraft. Junkers was one of several firms to respond, producing two separate design studies that produced both the Ju 85 and Ju 88. The design work was headed by Junkers' chief designer Ernst Zindel. The Ju 88 was envisioned to function as a so-called "Schnellbomber" ("fast bomber") that would evade interception by enemy fighters of its era by flying at high speed. On 21 December 1936, the first prototype performed its maiden flight. The performance of the third prototype was highly favourable, resulting in the competing Henschel Hs 127 and Messerschmitt Bf 162 being abandoned. During late 1937, the Ju 88 was developed into a heavy dive bomber, but this feat proved to be too stressful for the airframe even with modifications.
A series of technical problems troubled the aircraft's development, delaying its introduction to squadron service from 1938 to September 1939, by which point the Second World War had already started. The Ju 88 first saw action with the Luftwaffe during the invasion of Poland. It would subsequently be deployed into numerous theatres of the conflict, including the Norwegian campaign, the Battle of France, the Battle of Britain, the invasion of Yugoslavia, the invasion of Greece, the Siege of Malta, the North African campaign, and the Eastern Front amongst others. While the Luftwaffe was the primary operator of the Ju 88, numerous other nation's air services also flew the type in quantity during the war; these include the Finnish Air Force, "Regia Aeronautica" and the Royal Romanian Air Force.
The Ju 88 was one of the "Luftwaffe"'s most important and heavily used aircraft during the Second World War. The aircraft, akin to several other German bombers of the era, served as a bomber, dive bomber, night fighter, torpedo bomber, reconnaissance aircraft, and heavy fighter. Perhaps most unusually, it was adapted into a flying bomb towards the end of the war. The assembly line ran constantly from 1936 to 1945, building in excess of 15,000 Ju 88s across dozens of variants, making it the most-produced twin-engine German aircraft of the period and the second-most produced bomber of all time behind the four-engined Consolidated B-24 Liberator. Throughout its production run, the basic structure of the Ju 88 remained unchanged.
Design and development.
Background.
The origins of the Ju 88 can be traced back to the "Reichsluftfahrtministerium" (RLM) and the formulation of a new requirement in 1934 that called for a new multipurpose aircraft. This requirement quickly attracted attention from much of the German aircraft industry. However, in August 1935, the RLM revised its requirements towards the concept of a "Schnellbomber", a high-speed bomber that lacked defensive turrets, seated a crew of three, and carried a payload of . This requirement was issued to a total of four aircraft manufacturers, these being Focke Wulf, Henschel, Junkers, and Messerschmitt; all firms except Focke Wulf opted to produce a response.
Junkers design team opted to perform a pair of design studies in parallel; work began on 15 January 1936. These studies subsequently produced two distinct, yet similar, aircraft, designated "Ju 85" and "Ju 88". Both were twin-engined bomber aircraft, the main difference between the two being the Ju 85's use of a twin fin (and twin rudder) tail unit while the Ju 88 had a single fin (and rudder) tail unit instead. Following deliberation amongst officials, the RLM decided in favour of the Ju 88. According, the passed-over Ju 85 was never put into service.
The detailed design work was performed by Junkers chief designer Ernst Zindel. He was assisted by Wilhelm Heinrich Evers and American engineer Alfred Gassner. Evers and Gassner had worked together at Fokker Aircraft Corporation of America where Gassner had been Chief Engineer. Junkers presented their initial design in June 1936, and were given clearance to build two prototypes (Werknummer 4941 and 4942). The first two aircraft were to have a range of and were to be powered by two DB 600s. Three further aircraft, Werknummer "4943", "4944" and "4945", were to be powered by Jumo 211 engines. The first two prototypes, Ju 88 V1 and V2, differed from the V3, V4 and V5 in that the latter three models were equipped with three defensive armament positions to the rear of the cockpit, and were able to carry two bombs, one under each inner wing panel.
Into flight.
On 21 December 1936, the aircraft's maiden flight was performed by the prototype Ju 88 V1, which bore the civil registration D-AQEN. During its first flight, it managed to reach a speed of about . On 10 April 1937, the first prototype was lost in an accident. The third prototype, Ju 88 V3, which made its first flight on 13 September 1937 and was the first to be powered by the Jumo 211A engine, participated in a series of extensive tests at the Rechlin experimental station. According to the aviation authors J.R. Smith and Antony Kay, the results of this evaluation were so positive that all work on the competing Henschel Hs 127 and Messerschmitt Bf 162 was abandoned quickly thereafter.
Upon reviewing the Ju 88's performance, Hermann Göring, head of the "Luftwaffe", was reportedly ecstatic; it was allegedly viewed as an aircraft that could finally fulfil the promise of the "Schnellbomber". The streamlined fuselage was modelled after its contemporary, the Dornier Do 17, but furnished with fewer defensive guns as a result of the belief still held that it could outrun late 1930s-era fighters. During March 1939, the fifth prototype set a closed-circuit record while carrying a payload at a speed of .
The first five prototypes had conventionally-operating dual-strut leg rearwards-retracting main gear, however, starting with the V6 prototype, a main gear design debuted that twisted the new, single-leg main gear strut through 90° during the retraction sequence, much like that of the American Curtiss P-40 Warhawk fighter. This feature allowed the main wheels to end up above the lower end of the strut when fully retracted and was adopted as standard for all future production Ju 88s, and only minimally modified for the later Ju 188 and 388 developments of it. These single-leg landing gear struts also made use of stacks of conical Belleville washers inside them as their main form of suspension for takeoffs and landings.
By 1938, the design had received a series of radical modifications to adapt the Ju 88 to function as a "heavy" dive bomber in response to a request from the RLM. These changes, which were first implemented on the V8 and V9 prototypes, included the strengthening of the wings, the addition of dive brakes, an extended fuselage, and the number of crewmen being increased to four. 
During August 1938, "Generalluftzeugmeister" Ernst Udet had set out the Takt system of construction for large state-owned firms, including Junkers. Almost all of the tooling and jigs were produced at the company's facility in Schönebeck; the wing and tail sections were constructed at Halberstadt and Leopoldschall while the fuselage was originally produced as two separate shells that were brought together at Aschersleben. Later on, fuselage construction was broken down further, a decision that made it easier to produce the numerous variations of the Ju 88. During early 1939, a pre-production batch of ten Ju 88A-0s was completed to conduct service trials of the type; the A-0 series were almost entirely identical to the Ju 88 V10 prototype.
As the outbreak of the Second World War approached, by the time "Luftwaffe" planners such as Udet had their opportunities to have their own "pet" features added (including dive-bombing by Udet), the Ju 88's top speed had dropped to around . The Ju 88 V7 was fitted with cable-cutting equipment to combat the potential threat of British barrage balloons, and was successfully tested in this role; the V7 also had the Ju 88 A-1 "beetle's eye" faceted nose glazing installed, complete with the "Bola" undernose ventral defensive machine gun emplacement, and was put through a series of dive-bombing tests with bombs, and in early 1940, with bombs. The A-1 series prototypes were Wrk Nrs 0003, 0004 and 0005. The A-1s were given the Jumo 211B-1 or G powerplants.
The choice of annular radiators for engine cooling on the Ju 88, which placed these radiators immediately forward of each engine and directly behind each propeller, allowed the cooling lines for the engine coolant and oil-cooling radiators (integrated within the annular design) to be as short as possible, with integral port and starboard air intakes for cooling the exhaust headers, the starboard inlet also supplying the inlet air for the supercharger.
During autumn of 1938, Dr. Heinrich Koppenberg (managing director of Jumo) assured Göring that a production rate of 300 Ju 88s per month was definitely achievable; indeed, such a rate was achieved during 1940. However, the pre-war ramping up of production was delayed drastically by developmental problems. Although planned for a service introduction in 1938, the Ju 88 finally entered squadron service (with only 12 aircraft) on the first day of the invasion of Poland in 1939. Production was painfully slow at this point, only a single Ju 88 was being manufactured per week as problems kept cropping up. The Ju 88C series of heavy fighter was also designed in early 1940, but its existence was kept secret from Göring, as he only sought bombers at this time.
Dive bomber.
In October 1937, Ernst Udet had ordered the development of the Ju 88 as a heavy dive bomber. This decision was influenced by the success of the Ju 87 "Stuka" in this role. The Junkers development centre at Dessau gave priority to the study of pull-out systems and dive brakes. The first prototype to be tested as a dive bomber was the Ju 88 V4 followed by the V5 and V6. These models became the planned prototype for the A-1 series. The V5 made its maiden flight on 13 April 1938, and the V6 on 28 June 1938. Both the V5 and V6 were fitted with four-blade propellers, an extra bomb bay and a central "control system". Following the release of the bombs, the elevators automatically moved to their full-up position to bring the aircraft out of its dive and into a climb.
As a dive bomber, the Ju 88 was capable of pinpoint deliveries of heavy loads; however, despite all the modifications, dive bombing still proved too stressful for the airframe, and in 1943, tactics were changed so that bombs were delivered from a shallower, 45° diving angle. Aircraft and bomb sights were accordingly modified and dive brakes were removed. With an advanced "Stuvi" dive-bombsight, accuracy remained very good for its time. The maximum bomb load of the A-4 was , but in practice, standard bomb load was . Junkers later used the A-4 airframe for the A-17 torpedo carrier, which did not have the undernose "Bola" gondola for a ventral gun position.
Fighter-bomber.
The Ju 88C series of standard fighter-bomber versions from the C-2 onwards culminated in the Ju 88 C-6, applying experience acquired with the A-4 bomber, equipped with the same Jumo 211J engines but replacing the "beetle's eye" nose glazing with a smoothly curved all-metal nose, pierced only by the barrels of its forward-firing offensive armament. The C-6 was used mostly as fighter-bomber and therefore assigned to bomber units. As a reaction to the increasing number of attacks on German shipping, especially on U-boats in the Bay of Biscay, from July 1942 it started flying anti-shipping patrols and escort missions from bases in France.
"V./Kampfgeschwader 40" was specifically formed to operate the C-6. The aircraft of V./KG 40 (which was redesignated I./"Zerstörergeschwader" 1 in 1943) were a significant threat to antisubmarine aircraft and operated as escort fighters for the more vulnerable Focke-Wulf Fw 200 Condor maritime patrol bombers. Between July 1942 and July 1944, the Ju 88s of KG 40 and ZG 1 were credited with 109 confirmed air-to-air victories, at a cost of 117 losses. They were finally deployed against the Allied Invasion of Normandy in June 1944, incurring heavy losses for little effect before being disbanded