The Junkers Ju 188 was a German Luftwaffe high-performance medium bomber built during World War II, the planned follow-up to the Ju 88 with better performance and payload.
In 1936, Junkers submitted proposals for the Ju 85 and Ju 88 into competition for the new standardized Luftwaffe high-speed tactical bomber, known as the Schnellbomber (fast bomber).
The two designs were almost identical, differing only in that the Ju 85 used a twin-rudder and the Ju 88 a single fin.
At the same time, they offered modified versions of each as the Ju 85B and Ju 88B, again similar to the original designs but using an “egg shaped” stepless cockpit forward fuselage design that comprised a greenhouse-like, well-framed network of some three-dozen compound-curved window panels in total.
This was another example of the “bullet-nose” design philosophy that almost all new German bomber designs exhibited, from the time of the Heinkel He 111P onwards.
The new nose design for the Ju 88B also tightly integrated the forward end of the under-nose Bola ventral gondola defensive gun position into the newer nose design, when compared to the “added-on” Bola unit pioneered on the Ju 88 V7 prototype.
This meant the Ju 88B offered somewhat lower drag and better visibility.
At the time, this was considered too radical and the Ju 88A with its simpler, separately glazed dorsal cockpit “greenhouse” framed canopy, and “beetle’s eye” framed, multi-flat panel nose glazing comprising a “stepped” cockpit design from the separation of the pair of glazed units by the sheet metal of the upper fuselage nose winning the initial Schnellbomber production contract.
The Reich Air Ministry (RLM) was already in the process of looking for the replacement for the Schnellbomber, a new design that would be faster, fly higher, and have a larger payload.
This emerged as the “Bomber B” program, but this was extensively delayed due to the failure of the large 2,500 PS (1,800 kW; 2,500 hp)-class engines, like Junkers’ Jumo 222, to become reliable enough for production use.
Although Junkers’ Ju 288 was leading the contest, there was no delivery date on the engines.
To address the immediate need, the Ju 88B project was re-submitted as a stopgap.
For this version, they used the latest short-wing Ju 88 A-1 airframe as a baseline with the Ju 88B’s new stepless cockpit design, with the new Junkers Jumo 213 engine, which had recently started bench testing and was expected to deliver 1,500 PS (1,100 kW; 1,500 hp) and required a redesigned annular radiator system for engine and oil cooling.
The RLM also stipulated that the aircraft should also be able to accept the BMW 801 radial engine in a Kraftei (power-egg) unitized installation, with no modification to the engine nacelles.
The RLM was not impressed with the new design, as it offered only small improvements over the Ju 88A model in service but suggested that Junkers continue with the prototype work anyway and that they consider fitting the design with the BMW 139 radial.
This engine was cancelled only a few weeks later and all designs based on it moved to the newer and more powerful BMW 801.
Ju 188 A & E
The Ju 188 was designed to be fitted with either the 1,750 PS (1,290 kW; 1,730 hp) Jumo 213A or 1,700 PS (1,250 kW; 1,680 hp) BMW 801 G-2 engines without any changes to the airframe, with the exclusion of the re-design for Jumo-powered examples, of the annular radiators from their Jumo 211 layout for the A-series to better match the more powerful 213’s cooling needs, while using similar broad-chord three-blade propellers as the A-series did.
It was intended that both would be known as A models, but the naming was later changed: the Ju 188A model powered by the 213 and the Ju 188E by the 801.
It was planned all along to skip over a “B model” to avoid confusion with the original Ju 88 B but in the original plan the A and E models would be called As, and the Ju 188 C would be the next model.
The C series was built to the extent of a single example, by modifying one of the few A-1 machines.
A new power-operated, remotely operated FA 15 turret was mounted in the tail and had two 13 mm (0.512 in) MG 131s, aimed with a double-periscope (top and bottom) system mounted in the cockpit.
This modification would have greatly improved defensive firepower, always lacking on German designs but reliability was so poor it was decided to abandon the system.
Ju 188D & F
In early 1944, it was decided to focus on reconnaissance versions of the A and E models.
The airframe was modified with the removal of the bomb
aimer and forward gun and additional fuel cells were added to extend the range to 3,400 km (2,100 mi). The Ju 188 D-1 was otherwise similar to the A-1 and the Ju 188 D-2 had nose radar for naval reconnaissance.
Similar conversions of the E models were the Ju 188 F-1 and Ju 188 F-2.
Ju 188G & H
One problem with the Ju 88 that carried into the 188 was the lack of internal room for bomb storage.
Both carried the majority of their bomb load on racks under the wing, where it greatly affected performance.
This was to have been addressed in the G and H models, which extended the fuselage downward for more room with the addition of a wooden pannier.
The modification also left enough room at the tail to fit a manned turret in place of the C model’s remote-control one, but this system proved to be just as limited as the remote-control FA 15.
It was so small that only the smallest men could fit into it and left them with no room to escape in an emergency.
The RLM rejected the manned turret and planned on mounting the FA 15 even if it were unreliable.
Oddly, the designs still possessed the Bola under nose feature for a rear-facing gunner, when this would no longer be needed, and its removal would have greatly streamlined the aircraft.
With the Jumo 213s now being sent to fighter production, the Ju 188G-2 was to use the BMW 801 only, with the reconnaissance conversion known as the Ju 188 H-2.
Neither entered production before the war ended; the Ju 188G remained at the prototype stage.
Tail empennages of the few Ju 188G prototypes built were used in construction of the first two Ju 287 prototypes.
Ju 188 R
In the summer of 1944, three E models were modified as night fighters with the addition of radar and either four 20 mm MG 151/20s or two 30 mm (1.18 in) MK 103 cannons in the nose.
The better visibility of the 188 was not useful in night fighting and because the added drag of the radar washed out any speed difference, the Ju 188 R-0 was not ordered.