The dive-bomber was an American invention, but the Germans seized upon the concept as its accuracy offered the ability to destroy point targets such as bridges in the enemy rear. Only experience in Spain and Poland proved the Stuka's ability to provide fire support to troops operating beyond the range of field guns, the missing ingredient in the recipe for the blitzkrieg.
Stuka is actually a German abbreviation for dive-bomber (Sturzkampfflugzeuge), but became the nickname of the Ju 87 through propaganda accounts of its decisive role in the defeat of Poland. The first Ju 87, the Anton, entered service in two years earlier than that with three dispatched to Spain to experiment with dive-bombing techniques under live-fire conditions. It was a relatively crude-looking airplane with fixed landing gear enclosed in "trousers" and braced by struts. Powered by a 640 hp engine the Anton couldn't even reach 200 mph (322 kph), was armed only with one wing-mounted 7.92 machine-gun and another for rear defense, and could only carry a 1102 lb (500 kg) bomb if the gunner was left behind!
The Antons were quickly relegated to training units when the Bertas began to roll off the production line late the following year. The Berta was a major redesign of the basic airframe and used an engine almost twice as powerful. Although considerably more stream-lined than the earlier model since the landing gear was housed in sleeker "spats" and deletion of the under-carriage bracing, the Berta would generate an eerie whine as it dove at an angle approaching 90° onto its target as the wind whistled through the extended airbrakes. This was distinctly unnerving for troops unaccustomed to it. Later an actual siren was developed to exploit the effect, which wreaked havoc when the Germans invaded the West in May 1940, and provided people with the most indelible impression of the Stuka. The Berta could carry twice as much in bombs, carried a gun in the other wing, and was about 40 mph (65 kph) faster than the Anton.
Despite the extra speed the Berta was a sitting duck for modern fighters as the Battle of Britain proved where over 40 were shot down in only 6 days of operations! But in conditions where the Germans had air superiority the Stuka was prized for its accurately delivered munitions and ability to suffer severe damage and return home. The ungainly fixed under-carriage allowed it to operate from crude airstrips in mud or rainy weather that shut down faster and more capable aircraft.
The C model was developed to operate from the aircraft carrier Graf Zeppelin and differed from the Berta mainly in its jettisonable landing gear, to allow it to ditch without over-turning, folding wings and an arresting hook. Only 12 were built before the cancellation of the Graf Zeppelin rendered them moot.
The R model was built in parallel with the Berta as an effort to extend the range of the Stuka. Extra fuel tanks were fitted in the wing and two drop tanks could be carried under the wings. Externally identical to the Berta the R could carry the same bombload as its stablemate unless the extra fuel was used. The extra range proved deadly to the Royal Navy in its operations near Norway and Crete in the first years of the war as the R sank a number of warships. The R was the sole equipment of a few gruppen in the early campaigns, but seems to have been distributed fairly evenly between all the Stukagruppen for Barbarossa although III/Sturzkampfgeschwader 2 appears to have more than the others. It was phased out in 1942 along with the Berta with the introduction of the Dora since the latter incorporated the R's fuel system virtually without changes.
The Dora began deliveries in January 1942 to units on the Eastern Front. This had an up-rated 1400 hp engine and an increased bombload of nearly 4000 lbs (1800 kg) for short-range missions. Protection for the air crew increased with additional armor and replacement of the rear armament and its mount with an armored GSL-K 81Z turret mounting a twin-barreled MG 81Z 7.92mm machine-gun. The fuel system was similar to that of the R model with wing tanks that increased normal range to 510 miles (822 km). Underwing drop tanks extended the Dora's maximum range to 954 miles (1538 km).
Much effort was devoted to streamlining the Dora, one example being the repositioning of the Berta's massive chin radiator to positions underneath the wings and the oil cooler mounted in its place, but maximum speed only increased to 255 mph (410 kph) As part of this effort the landing gear redesigned to handle the increased weight in a trimmer installation which proved to be rather less sturdy than the Berta's.
The D-2 sub model was designed as a dedicated glider tug with a strengthened rear fuselage although almost any Ju 87 could be fitted with the appropriate hardware.
The D-3 featured more armor, protecting the engine, radiators, and fuselage belly as the Stuka was being used more in the the low-level attack role. The dive sirens which so discomfited Allied troops in the early years of the war were removed because they had lost their effectiveness.
Some D-1s and D-3s were modified as D-4s to carry a torpedo, but the torpedo attack role was better filled by the faster He 111H and Ju 88A bombers which could also carry more torpedoes. All D-4s were reconverted back to D-1 and D-3 standard without ever flying an operational sortie.
The D-5 sub model began to delete the dive brakes as unnecessary since they weren't used much. By mid-'43 when the D-5 was introduced the Stukas were more often used in the close-support role than as dive-bombers. Presumably this was due to the loss of total air superiority by the Luftwaffe so that the Stukas couldn't climb to the altitudes needed to dive-bomb properly without fighter escort, but ground-level attack missions could go on regardless. The D-5 also replaced its wing-mounted 7.92mm machine guns with 20mm cannon, had extended wings to reduce the wing loading and re-introduced the jettisonable undercarriage of the Clara to make belly landings safer.
As the aerial environment became less hospitable for the Doras they were transferred to night ground-attack units (Nachtschlachtgruppen) where their disadvantages were less apparent. The D-7s and D-8s flown by these units were modified from D-3s and D-5s respectively by the substitution of a 1500 hp engine and the addition of flame dampening tubes for the engine exhaust. These aircraft usually operated in flare-dropper/attack teams or under ground-based radio control, the latter referred to as the Egon procedure. The former method required one aircraft to drop flares to illuminate or silhouette the target so it could be attacked by the other aircraft. This was very similar to the method adopted by the British Fleet Air Arm for its night torpedo and bombing strikes, Taranto being the best-known example.
However some Stukas still flew by day as their special abilities required. These Gustav models were specialized tank killers, nicknamed the Panzerknacker (tank cracker) or Kanonenvogel (cannon bird). G-1s were minimal conversions from D-3s while G-2s were rebuilt D-5s that were much cleaner aerodynamically than the G-1. A pair of underwing Flak 18 37mm flak guns were mounted with 12 rounds per gun, the normal wing armament generally being deleted to save weight. The 37mm guns proved capable of destroying all but the heaviest Soviet tanks with their tungsten-cored shells. The Panzerknackers were extremely vulnerable to enemy fighters, but they flew on regardless until the end of the war.
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