Despite the Stuka’s vulnerability to enemy fighters having been exposed during the Battle of Britain, the Luftwaffe had no choice but to continue its development, as there was no replacement aircraft in sight. The result was the D-series. In June 1941, the RLM ordered five prototypes, the Ju 87 V21-25. A Daimler-Benz DB 603 powerplant was to be installed in the Ju 87 D-1, but it did not have the power of the Jumo 211 and performed “poorly” during tests and was dropped. The Ju 87 D-series featured two coolant radiators underneath the inboard sections of the wings, while the oil cooler was relocated to the position formerly occupied by the coolant radiator. The D-series also introduced an aerodynamically refined cockpit with better visibility and space. In addition, armour protection was increased and a new dual-barrel 7.92 mm (.312 in) MG 81Z machine gun with an extremely high rate of fire was installed in the rear defensive position. Engine power was increased again, the Jumo 211J now delivering 1,420 PS (1,044 kW, 1,401 hp). Bomb carrying ability was massively increased from 500 kg (1,100 lb.) in the B-version to 1,800 kg (3,970 lb.) in the D-version (max. load for short ranges, overload condition), a typical bomb load ranged from 500-1,200 kg (1,100-2,650 lb.).
The internal fuel capacity of the Ju 87D was raised to 800 L (of which 780 L were usable) by adding additional wing tanks while retaining the option to carry two 300 L drop tanks. Tests at Rechlin revealed it made possible a flight duration of 2 hours and 15 minutes. With an extra two 300 L (80 US gal) fuel tanks, it could achieve four hours flight time.
The D-2 was a variant used as a glider tug by converting older D-series airframes. It was intended as the tropical version of the D-1. It was to have heavier armour to protect the crew from ground fire. The armour reduced its performance and caused the Oberkommando der Luftwaffe to “place no particular value on the production of the D-2”. The D-3 was an improved D-1 with more armour for its ground-attack role. A number of Ju 87 D-3s were designated D-3N or D-3 trop and fitted with night or tropical equipment. The D-4 designation applied to a prototype torpedo-bomber version, which could carry a 750-905 kg (1,650-2,000 lb.) aerial torpedo on a PVC 1006 B rack. The D-4 was to be converted from D-3 airframes and operated from the aircraft carrier Graf Zeppelin. Other modifications included a flame eliminator and, unlike earlier D variants, two 20 mm MG 151/20 cannon, while the radio operator/rear gunner’s ammunition supply was increased by 1,000 to 2,000 rounds.
The Ju 87 D-5 was based on the D-3 design and was unique in the Ju 87 series as it had wings 0.6 metres (1 foot) longer than previous variants. The two 7.92 mm MG 17 wing guns were exchanged for more powerful 20 mm MG 151/20s to better suit the aircraft’s ground-attack role. The window in the floor of the cockpit was reinforced and four, rather than the previous three, aileron hinges were installed. Higher diving speeds were obtained of 650 km/h (408 mph) up to 2,000 m (6,560 ft.). The range was recorded as 715 km (443 mi) at ground level and 835 km (517 mi) at 5,000 m (16,400 ft.).
The D-6, according to “Operating instructions, works document 2097”, was built in limited numbers to train pilots on “rationalised versions”. However, due to shortages in raw materials, it did not go into mass production. The D-7 was another ground attack aircraft based on D-1 airframes upgraded to D-5 standard (armour, wing cannons, extended wing panels), while the D-8 was similar to the D-7 but based on D-3 airframes. The D-7 and D-8 were both were fitted with flame dampers, and could conduct night operations.
Production of the D-1 variant started in 1941 with 495 ordered. These aircraft were delivered between May 1941 and March 1942. The RLM wanted 832 machines produced from February 1941. The Weserflug Company was tasked with their production. From June to September 1941, 40 Ju 87 Ds were expected to be built, increasing to 90 thereafter. Various production problems were encountered. Just one of the planned 48 was produced in July. Of the 25 the RLM hoped for in August 1941, none were delivered. Only in September 1941 did the first two of the planned 102 Ju 87s roll off the production lines. The shortfalls continued to the end of 1941. During this time, the WFG plant in Bremen moved production to Berlin. Over 165 Ju 87s had not been delivered and production was only 23 Ju 87 Ds per month out of the 40 expected. By the spring of 1942 to the end of production in 1944, 3,300 Ju 87s, mostly D-1s, D-2s and D-5s had been manufactured.
Total production amounted to 3639 Ju 87D (592 D-1, 1559 D-3 and 1448 D-5), all built by Weserflug. The last Ju 87 D-5 rolled off the production lines in September 1944.
The Ju 87 E and F proposals were never built, and Junkers went straight onto the next variant. Another variant derived from the Ju 87D airframe, the Ju 87H saw service as a dual-control trainer.
In January 1943, a variety of Ju 87 Ds became “test beds” for the Ju 87 G variants. At the start of 1943, the Luftwaffe test centre at Tarnewitz tested this combination from a static position. Oberst G. Wolfgang Vorwald noted the experiments were not successful, and suggested the cannon be installed on the Messerschmitt Me 410. However, testing continued, and on 31 January 1943, Ju 87 D-1 W. Nr 2552 was tested by Hauptmann Hans Karl Stepp near the Briansk training area. Stepp noted the increase in drag, which reduced the aircraft’s speed to 259 km/h (162 mph). Stepp also noted that the aircraft was also less agile than the existing D variants. D-1 and D-3 variants operated in combat with the 37 mm (1.46 in) BK 37 cannon in 1943.
- Ju 87 V 21. Registration D-INRF. W.Nr 0870536. Airframe conversion from B-1 to D-1.First flown on 1 March 1941.
- Ju 87 V 22 Stammkennzeichen of SF+TY. W.Nr 0870540. Also airframe conversion from B-1 to D-1. First flown on 1 March 1941.
- Ju 87 V 23 Stammkennzeichen of PB+UB. W.Nr 0870542. Also airframe conversion from B-1 to D-1. First flown on 1 March 1941.
- Ju 87 V 24 Stammkennzeichen of BK+EE. W.Nr 0870544. Also airframe conversion from B-1 to D-1/D-4. First flown on 1 March 1941.
- Ju 87 V 25 Stammkennzeichen of BK+EF. W.Nr 0870530. Also airframe conversion from B-1 to D-4 trop. First flown on 1 March 1941.
- Ju 87 V 30, the only known prototype of the Ju 87 D-5. W.Nr 2296. First flown on 20 June 1943.
- Ju 87 V 26-28, Ju 87 V 31, and V 42-47 were experiments of unknown variants.
With the G variant, the aging airframe of the Ju 87 found new life as an anti-tank aircraft. This was the final operational version of the Stuka, and was deployed on the Eastern Front. The reverse in German military fortunes after 1943 and the appearance of huge numbers of well-armoured Soviet tanks caused Junkers to adapt the existing design to combat this new threat. The Hs 129B had proved a potent ground attack weapon, but its large fuel tanks made it vulnerable to enemy fire, prompting the RLM to say “that in the shortest possible time a replacement of the Hs 129 type must take place.” With Soviet tanks the priority targets, the development of a further variant as a successor to the Ju 87D began in November 1942. On 3 November, Erhard Milch raised the question of replacing the Ju 87, or redesigning it altogether. It was decided to keep the design as it was, but to upgrade the powerplant to a Jumo 211J, and add two 30 mm (1.18 in) cannon. The variant was also designed to carry a 1,000 kg (2,200 lb.) free-fall bomb load. Furthermore, the armoured protection of the Ilyushin Il-2 Sturmovik was copied, to protect the crew from ground fire now that the Ju 87 would be required to conduct low level attacks.
Hans-Ulrich Rudel, a Stuka ace, had suggested using two 37 mm (1.46 in) Flak 18 guns, each one in a self-contained under-wing gun pod, as the Bordkanone BK 3.7, after achieving success against Soviet tanks with the 20 mm MG 151/20 cannon. These gun pods were fitted to a Ju 87 D-1, W. Nr 2552 as “Gustav the tank killer”. The first flight of the machine took place on 31 January 1943, piloted by Hauptmann Hans-Karl Stepp. The continuing problems with about two dozens of the Ju 88P-1, and slow development of the Hs 129 B-3, each of them equipped with a large BK 7.5 cm (2.95 in) cannon in a conformal gun pod beneath the fuselage, meant the Ju 87G was put into production. In April 1943, the first production Ju 87 G-1s were delivered to front line units. The two 37 mm (1.46 in) cannons were mounted in under-wing gun pods, each loaded with a six round magazine of armour-piercing tungsten carbide ammunition. With these weapons, the Kanonenvogel (“cannon-bird”), as it was nicknamed, proved spectacularly successful in the hands of Stuka aces such as Rudel. The G-1 was converted from older D-series airframes, retaining the smaller wing, but without the dive brakes. The G-2 was similar to the G-1 except for use of the extended wing of the D-5. 208 G-2s were built and at least a further 22 more were converted from D-3 airframes.
Only a handful of production Gs were committed in the Battle of Kursk. On the opening day of the offensive, Hans-Ulrich Rudel flew the only “official” Ju 87 G, although a significant number of Ju 87D variants were fitted with the 37 mm (1.46 in) cannon, and operated as unofficial Ju 87 Gs before the battle. In June 1943, the RLM ordered 20 Ju 87Gs as production variants. The G-1 later influenced the design of the A-10 Thunderbolt II, with Hans Rudel’s book, Stuka Pilot being required reading for all members of the A-X project.
The Soviet Air Force practice of harassing German ground forces using antiquated Polikarpov Po-2 and R-5 biplanes at night to drop flares and fragmentation bombs, inspired the Luftwaffe to form its own Störkampfstaffeln (harassment squadrons). On 23 July 1942, Junkers offered the Ju 87 B-2, R-2 and R-4s with Flammenvernichter (“flame eliminators”). On 10 November 1943, the RLM GL/C-E2 Division finally authorised the design in directive No. 1117. This new equipment made the Ju 87 more difficult to detect from the ground in darkness.
Pilots were also asked to complete the new “Blind Flying Certificate 3”, which was especially introduced for this new type of operation. Pilots were trained at night, over unfamiliar terrain, and forced to rely on their instruments for direction. The Ju 87’s standard Revi C12D gunsight was replaced with the new Nachtrevi (“Nightrevi”) C12N. On some Ju 87s, the Revi 16D was exchanged for the Nachtrevi 16D. To help the pilot see his instrument panel, a violet light was installed. On 15 November 1942, the Auxiliary Staffel were created. By mid-1943, Luftflotte 1 was given four Staffeln while Luftflotte 4 and Luftwaffe Kommando Ost (Luftwaffe Command East) were given six and two respectively. In the first half of 1943, 12 Nachtschlachtgruppen had been formed, flying a multitude of different types of aircraft, including the Ju 87, which proved itself ideally suited to the low-level slow flying needed.