It was produced only in limited numbers, due both to the presence of improved versions of the Ju 88, as well as the increasingly effective Allied strategic bombing campaign against German industry and the resulting focus on fighter production.

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 sheetmetal 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 warload.

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.

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 fuselage and tail surfaces were identical to the Ju 88 A-1, which presented a problem: with the extra power, 1,560 PS (1,150 kW; 1,540 hp), the design could now carry considerably more load than the small bomb bay could fit.

The A-4 used a longer wing of 20.08 m (65.9 ft) span from new rounded wingtips for better altitude performance, when compared to the initial Ju 88A-1's shorter 18.26 m (59.9 ft) span, but attention to streamlining and new pointed wing tips, somewhat resembling those fitted to the British Spitfire Mks.VII and VIII for their own intended high-altitude flight requirements, kept drag to about what it was earlier.

One of these was fitted with the slightly updated 801L engines and a small power-operated turret on the extreme top of the cockpit mounting a 13 mm (0.512 in) MG 131 machine gun.

Two other airframes had their engines and outer wings removed to act as testbeds for water ditching, as it was planned to use the Ju 188 in long overwater flights against British shipping.

Concerns about the Jumo 213, now years overdue, were offset by this engine's better altitude performance, so it made sense to delay the aircraft slightly if that meant it could switch to the 213 as soon as they became available.

[3] 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.

By the time deliveries were finally picking up in late 1943, the Jumo was available in a new MW 50 methanol-water injection "boosted" version that delivered 1,648 kW (2,241 PS; 2,210 hp) for takeoff.

The dorsal turret had only one gun, yet the type retained the single-gun flexible position only a few centimeters away from it; various projects finally to provide the 188 with tail armament were abandoned.

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.

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).

[7] Oddly, the designs still possessed the Bola undernose feature for a rear-facing gunner, when this would no longer be needed and its removal would have greatly streamlined the aircraft.

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.

Before any of these could start production, the entire lineup was renamed the Ju 388, the vastly improved performance warranting a different 8-388 airframe number from the RLM for the design.