WW2 German Prototypes

Flakpanzer IV (3.7 cm Zwillingflak 43) ‘Ostwind II’

Germany (1945)
Self-Propelled Anti-Aircraft Gun – Possibly 1 Prototype Built

In the later stages of the Second World War, the Germans lost control over the skies and their ground forces had to endure extensive enemy air attack raids. The use of self-propelled anti-aircraft guns (SPAAG) based on half-track chassis offered some way to fight back, but these were themselves highly vulnerable, as they lacked proper armor protection. A SPAAG based on a tank chassis was more desirable. Starting from 1944, the German focus was on producing vehicles based on the Panzer IV chassis. The vehicle known as the Ostwind (Eng. Eastwind) was one of them, armed with a single 3.7 cm anti-aircraft gun placed in an open-topped turret. In the hopes of further increasing its firepower, the Germans tested the installation of two 3.7 cm guns in a modified turret which led to possibly the creation of a single Ostwind II prototype.

An Ostwind II drawing- There are no known surviving pictures of it, and even the construction of a single prototype is debated. Source: Pinterest

A Brief History of the Flakpanzer IV Ostwind

The first real effort to create a self-propelled anti-aircraft vehicle based on a tank chassis, known as a Flakpanzer in German, was the Flakpanzer 38(t). While it was built in some numbers, its design was unsuccessful given the weak firepower, lack of a fully protected turret, and its overall small size. The Panzer IV chassis was deemed more suitable for this task. The first such vehicle, known as the Möbelwagen to its crews, while having a good gun, suffered from the same problems as the previous vehicle. It needed time to properly set up for firing, which reduced its combat effectiveness. For these reasons, the German Army focused on developing a Flakpanzer based on the Panzer IV having a fully rotating and protected turret. This would lead to the creation of two similar vehicles. The first introduced was the so-called Wirbelwind, armed with four 2 cm anti-aircraft guns. The second vehicle was the Ostwind, which was quite similar in appearance, being armed with a single 3.7 cm anti-aircraft gun. Both vehicles were quite simple in design and simply replaced the original Panzer IV turret with an open-top turret with the main gun placed in it.

Unusually, the Ostwind, similar to the Wirbelwind, was developed and built by the German Army itself, without the inclusion of any commercial firms. Due to the worsening economic situation, the use of newly produced tank chassis was limited at best, so repaired and returned from the front chassis had to be reused for this project. While vehicles such as the Ostwind were in great demand, there were huge delays in production, which hindered its introduction to service. By the time the war ended, only between 6 and 43 such vehicles are believed to have been built, seeing limited combat action.

The 3.7 cm Flak 43 Flakpanzer IV, better known as Ostwind. Source:

An Improved Model

The general development history of the Ostwind II vehicle is, sadly, quite poorly documented in the sources, with very little information available. What is known is that it was developed by the Ostbau-Sagan workshop from Silesia, which was also involved in the development of the Ostwind Flakpanzer. The main weapon was provided by Gustloff-Werke from Suhl. The request to develop a Flakpanzer armed with two 3.7 cm anti-aircraft guns was given by Adolf Hitler in 1943. During May 1944 several wooded mock-up Flakpanzer projects were presented to a military delegation led by Heinz Guderian. One of these was a wooden mock-up of a Flakpanzer IV armed with 3.7 cm Flakzwilling 43 in its original configuration developed by Alkett. The delegation rejected this project and focused instead on the Wirbelwind, which was also presented at that time. The development of a Flakpanzer IV armed with two 3.7 cm anti-aircraft guns resumed sometime at the end of 1944. The first working prototype was completed only in January 1945. Unfortunately, besides a few drawings, no known photographs are believed to have survived to this day, and questions remain as to if even a prototype was built at all.


The name of this vehicle is often described as being Ostwind II. Due to the lack of information in the sources, it is almost impossible to determine if this was an official or post-war invented designation. This article uses the Ostwind II designation, mostly for the sake of simplicity.



The Ostwind II, like its predecessor, would be made using modified Panzer IV chassis. Due to the worsening situation with the war, new chassis could not be spared for projects besides the original tank configuration. The chassis used would have varied depending on what was available on hand. This would most likely have included the Panzer IV Ausf.H and J chassis, but out of necessity, older chassis may have also been used.


The suspension and running gear were the same as those of the original Panzer IV, with no changes to its construction. It consisted of eight pairs of small road wheels on each side, with every two pairs suspended by leaf-spring units. There was a front-drive sprocket, a rear idler, and three to four (depending on the model used) return rollers per side.


The engine was the Maybach HL 120 TRM, which produced 272 hp at 2,800 rpm. The original Ostwind had a weight of 25 tonnes. The improved version would have been heavier than that by about 1.5 tonnes, given the extra weight of the main armament. The new crew member should also be included, but also any additional spare ammunition needed to load the two guns. This would likely affect the overall driving performance, but to which extent is difficult to tell without any explicit source.


The upper tank hull was unchanged from the original Panzer IV. The driver’s front observation hatch and the ball-mounted hull machine gun remained the same as well. The installation of the main armament would most likely be a direct copy of the Ostwind, possibly with some minor modifications, such as strengthening the overall construction of the mount, given the extra weight added by the gun and the additional crew member. Two, or even more, in order to cope with the extra weight, metal beams were welded inside the Panzer IV hull to make a stable platform on which the twin 3.7 cm guns were placed.


Depending on the chassis used for the Ostwind II, there may have been slight differences in armor thickness. In general, the later built Panzer IVs had a maximum frontal armor thickness of 80 mm. The sides were much thinner, at 30 mm, while the rear was 20 mm thick.


The Ostwind II turret design would have been quite similar to the previous version in visual appearance, with some differences. The turret was open-topped, in order to provide a better view of the surroundings and to reduce overall construction costs. This would have also helped remove the gun fumes properly, as the Germans never properly developed a full-enclosed anti-aircraft turret with an adequate ventilation unit. The turret consisted of 12 welded armor plates. Due to the new gun and the additional crew member, its overall internal layout and its size had to be changed slightly. In addition, as the two guns were placed side by side, two new openings to the front armor had to be made. There would also be a small hatch for the gun operator’s sight, placed on the right front side of the turret.

The Ostwind II turret would have been quite similar in appearance to its predecessor, with some differences. This would include two openings for the guns, external changes, and probably even its overall size. Source:

The turret traverse mechanism would most likely be a copy of the one used on the Ostwind, which is itself poorly documented. A steering rod was used to connect the twin Flak guns’ traversing mechanism and the Panzer IV turret ring. This allowed the crew to move the turret by using the gun traverse. The turret would be placed on a ring-shaped turret base welded to the hull top, with added ball bearings to help with the rotation. It is unknown if the Ostwind II would have the pyramid-shaped sheet of armor welded to the lower part of the front turret. Its purpose was to provide additional protection against any possible ricochets from smaller caliber rounds in the direction of the vehicle’s hull.

The turret armor protection would probably have remained the same as on the first version in order to save time and resources. The armor thickness would have been 16 mm of all-around armor placed at a 30° angle. The secondary sources disagree on the turret armor thickness, as both 16 mm and 25 mm of armor are often attributed. For example, W. J. Spielberger (Gepard, The History of German Anti-Aircraft Tanks) mentions that the armor thickness was originally 16 mm, but later, during production, it was increased to 25 mm. T. L.Jentz and H. L. Doyle (Panzer Tracts No. 12-1 – Flakpanzerkampfwagen IV and other Flakpanzer projects development and production from 1942 to 1945) list that it was 16 mm thick.


The main weapon used was the 3.7 cm Zwillingflak 43 (also sometimes called Zwillingflak 44). This weapon was basically just two 3.7 cm Flak 43s placed one above the other. Although sharing the same 3.7 cm caliber as the earlier Flak 18, 36, and 37 models, the newer Flak 43 (built by Rheinmetall-Borsig) was a completely different weapon. The primary goal of this design was to be simple to operate and easy to produce. It had a new gas-operated breech mechanism, which was loaded with a fixed loading tray with eight-round clips.

The Zwillingflak 43 was built-in smaller numbers during the closing years of the war. Source:

What is somewhat unusual is that this gun was not placed in its original configuration, but instead side by side, with some 30 cm distance between the two barrels. This is odd, as it would have been much easier to just install the gun as it was into the Ostwind II turret. The most obvious reason for this kind of installation was reducing the overall height. With such an over-and-under configuration, in order to load the upper gun, the loader would have to stand up, which would expose him to enemy fire. In addition, with a height of nearly 3 m, the Ostwind’s weakly armored turret was too exposed to enemy fire. Raising the turret height would only increase the chances of being hit by enemy fire. Another reason would have been the difficulty of putting two loaders on the same side in the relatively cramped turret. The side-by-side configuration may have complicated production and development, but would at least offer more effective use of internal turret space.

The gun itself had to be modified in order to fit inside the turret. The lower part of the carriage and the original gun shield were removed. In order to cover the two front embrasure openings, smaller rectangular shields would be placed in front of each gun barrel. In addition, the spent ammunition baskets had to be smaller.

The Zwillingflak 43 could rotate a full 360°, with a range of gun elevation between – 10° to + 90°. The maximum rate of fire was 500 rounds per minute, but 360 was a more practical rate. With a muzzle velocity of 820 mps, the maximum effective ceiling was 4,800 m. The ammunition load is unknown, but in order to feed the two guns, it (at least in theory) had to be increased from the previous version. The Ostwind ammunition load differs between sources, ranging from 400 up to 1,000 spare rounds. It is possible that an ammunition trailer may have been used on the Ostwind II, but how practical it would be in a real combat situation would be questionable. It must not be forgotten that the German economy in 1945 was in a complete state of chaos and ammunition or fuel stocks were in short supply. For self-defense, the crew could rely on the hull-mounted MG 34, retained from the Panzer IV design, and their personal weapons.

Author D. Nešić (Naoružanje Drugog Svetsko Rata-Nemačka) mentioned that the Ostwind II was armed with two 3 cm Flakvierling MK 103 anti-aircraft guns. He also mentioned that the ammunition load was 2,800 rounds. This is most likely erroneous, mistaking it with the Destroyer 45 based on the Wirbelwind. He also mentioned two 3 cm guns, when ‘Flakvierling’ actually means four guns.


The crew of the Ostwind II would likely consist of a commander, gunner, radio operator, driver, and loader. The driver and radio operator were placed in the vehicle’s hull. For the radio operator, the Fu 5 and Fu 2 radio equipment were provided. In addition, the radio operator also operated the hull-mounted machine gun.

The positions of the remaining crew members are not listed in the sources. But, given its gun main characteristics, their positions can be deduced. The 3.7 cm Flak 43 gunner position was on the right side, with the position somewhere on the right of the turret. As the two guns were placed side by side, the two loaders had to be placed opposite each other. While two loaders would be needed to properly feed the main guns, it is possible that, due to lack of personnel or space, the commander may have acted as the loader on the left side. This would hinder the main command task, but would provide more working room in the otherwise cramped turret. Given the lack of information, this is merely speculation. The commander would be placed on the left rear side of the turret. The working conditions in the Ostwind II turret would be quite difficult due to the lack of working space. This was actually a problem even on the previous Ostwind vehicle, and was never effectively solved.

The Ostwind II turret crew consisted of three (four, according to some sources) men, with the gunner placed on the right and the commander and the loader opposite him. The Ostwind II would probably have had to have room for extra crew members needed to feed the guns. Source:

The Fate of the Project

According to Walter J. Spielberger (Gepard, The History of German Anti-Aircraft Tanks), once the prototype was completed, it was, together with the improved Wirbelwind (known as Zerstörer 45, Eng. Destroyer), transported to the training center at Ohrdruf, in Thuringia. What happened to them after this point is not clear. Due to the chaos and destruction of the late stages of the war, they may have been used as part of an ad hoc unit in order to fight the advancing Allied formations. It is more likely that they did not see any action, given their experimental nature.

It is also important to consider the fact that the whole Ostwind II construction may have also ended in failure. The installation of two 3.7 cm guns in the cramped modified Ostwind turret may have not been possible. It is also possible that the often mentioned prototype did not even have a fully operational turret and was just used to see if the whole installation was even feasible. As such, some, including Hilary L. Doyle, have speculated that not even a prototype was built, alleging Germany’s almost non-existent industrial capacity at the time. H. L. Doyle expressed suspicion that by 1945 the Germans had industrial capabilities to actually build the Ostwind II vehicle, so it seems unlikely that even one fully operational prototype was ever completed.

Other sources, including author D. Terlisten (Nuts and Bolts Vol.13 Flakpanzer, Wirbelwind and Ostwind) mentions a report from Ostbau-Sagan discovered after the war that mentions that some turrets (plural, although the precise number is not listed) for the Ostwind II were completed. D. Nešić, (Naoružanje Drugog Svetsko Rata-Nemačka) mentions that one prototype was built and that a production order for 100 vehicles was given, which did not materialize due to the end of the war.

Overall, for several reasons, the production of the new Ostwind II was not possible. Due to the Allied advance, the Ostabu-Sagan facility had to be evacuated to Teplitz-Schonau in occupied Czechoslovakia. This caused major delays and confusion during the Flakpanzer production. The lack of resources and spare Panzer IV chassis was also a major issue, not to mention the general lack of spare ammunition and fuel at this stage of the war.


The Ostwind II was certainly an interesting Flakpanzer design. It could have provided the Germans with a vehicle with sufficient firepower to be a serious threat to the Allies. In reality, it is not clear if the whole installation was without any mechanical issue. Another problem was its late conception, with a possible prototype being completed at the start of 1945, though even this is questionable. Given the chaotic state of Germany at that time, serial production would not have been possible.

Flakpanzer IV 3.7 cm Zwillingflak 43 ‘Ostwind II’ Illustratied by Godzilla funded by our Patreon Campaign.



Dimensions 5.92 x 2.9 x 2.9 m
Total weight, 25 to 27 tonnes
Crew 6 (Commander, Gunner, Two Loaders, Radio Operator, and Driver)
Primary Armament 3.7 cm Zwillingflak 43
Secondary Armament 7.92 mm MG 34
Propulsion Maybach HL 120 TR(M) 265 HP @ 2,600 rpm
Armor 10 to 80 mm



4 replies on “Flakpanzer IV (3.7 cm Zwillingflak 43) ‘Ostwind II’”

There is a minor typo second paragraph of the armament section, weekly instead of weakly when referring to the armor of the vehicle’s turret.

Actually, the navy guns are completely different from the same caliber anti-acraft gun used by the German Army.

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