SPG and Fold-out AA Gun

Medium SPGs on the PzIV chassis designed by Krupp engineers were seemingly cursed. The Pz.Sfl.IVa "bunker buster" only had two prototypes built, and work on the Pz.Sfl.IVb ended after a pilot batch. Nevertheless, both vehicles made it to the front lines. The fate of the Pz.Sfl.IVc was similar. Initially, the vehicle was designed as a bunker buster, then as a medium SPAAG. In the end, only one prototype was built, which underwent conversion and was sent to the front.

A useless necessary SPG

Krupp's "self propelled gun mounts" arose from the German military's need of a means to combat long term fortifications (pillboxes). These fortifications were common along Germany's borders with France, Belgium, and Czechoslovakia. Towed artillery could be used to fight them, but it is unlikely that the enemy would sit and patiently wait while the crew would move the gun from travel to firing position and begin to shoot. An SPG that would take very little time to bring into action would be very useful for this task. The first such vehicle was the 10.5 cm K. L/52 Selbstfahrlafette, armed with a 105 mm K 18 gun. Later, this vehicle was renamed Pz.Sfl.IVa.

8.8 cm Flak 18 Sfl. auf 12 to Zugkraftwagen, the first mass produced German medium SPG.

While Krupp was designing their bunker buster, a search for faster decisions went on in parallel. The mass produced universal 8.8 cm Flak 18 was considered. This AA gun was among the best in its class. A decision was made in 1938 to reclassify it as a dual purpose weapon, meant to fire not only at airborne, but also at ground targets. For this, armour piercing ammunition with excellent penetration was introduced. No tank in the world at the time had enough armour to resist this weapon. However, the gun had two major drawbacks: its weight, nearing five tons, and a tall silhouette.

Two different solutions were proposed to increase the mobility of the 8.8 cm Flak 18 in the bunker busting role. The first consisted of a gun shield, some changes to the mount, and the use of the partially armoured Sd.Kfz.7 prime mover to tow it. The second was a more radical solution: the gun was installed in the bed of a 12 ton Sd.Kfz.8 prime mover. The mass of this vehicle reached 17 tons. It had many significant drawbacks, but one advantage: it could be built very quickly.

Both solutions went into production. 10 of the first German medium SPG were ready by the end of 1938. Even though the vehicle, named  8.8 cm Flak 18 Sfl. auf 12 to Zugkraftwagen, proved itself to be an effective anti-tank measure, it was obvious that this was only a temporary solution.

The barrel of an 88 mm gun that was to be installed on the Pz.Sfl.IVc, July 1941.

Krupp began work on self propelled gun mounts back in 1938, and the first drafts were ready in April of 1939. Soon, work on the 10.5 cm K. L/52 Selbstfahrlafette turned into a battle between Krupp and the 6th Department of the Armaments Directorate. The department's head, Heinrich Kniepkamp, had a different vision than Krupp's engineers. According to him, the chassis should have a torsion bar suspension, six road wheels per side, and have high mobility.

Attempts to increase mobility ran into the need to install a more powerful engine, since the dimensions of the vehicle were strictly limited. As for a torsion bar suspension, Krupp's engineers were strongly against it. Some variants of the Pz.Sfl.IVa had six road wheels per side, but the designers finally settled on a regular PzIV Ausf. D-E chassis. The concept with six wheels per side was later used on the Pz.Slf.IVb 105 mm SPG, the design of which entered the active phase in the fall of 1939.

A third project appeared around the same time, the Pz.Sfl.IVc. This vehicle was meant to combat pillboxes and was armed with a gun that mirrored the ballistics of the 8.8 cm Flak 18. Alas, nearly no documents regarding its initial design remain. It is known that three vehicles were ordered by the military, and that after the fall of France they were considered as tank destroyers instead. They now needed high mobility, for which armour could be sacrificed. The thickness of the Pz.Sfl.IVc's armour was about the same as that of the Pz.Sfl.IVb: 20 mm in the front.

The 8.8 cm Pak 43 Kfz. As of 1942, this weapon was considered for use in the Pz.Sfl.IVc.

The design of the Pz.Sfl.IVc began to settle towards the summer of 1941. The demand to make it as mobile as possible led to an unusual chassis. A significant part of the hull turned into a flat platform. The engine was left under the floor in the rear of the hull, as were the air intakes. The enclosed driver's compartment was in the front.

The suspension was also another unusual part. Its development began in late 1940. By that point, Heinrich Kniepkamp fully moved into using torsion bar suspensions and interleaved road wheels in all new designs. Krupp's engineers agreed with the interleaved road wheels, but not with the torsion bars. A new suspension was born. It consisted of eight pairs of 700 mm interleaved road wheels. However, the suspension elements were the same as on the PzIV. The width of the track links grew to 422 mm. The suspension was to be tested on two PzIV Ausf. E tanks in 1941, but the trial vehicles were only built by June of 1942. The width of the tracks was constantly being revised, and finally settled at 420 mm.

The only image of the Pz.Sfl.IVc as a tank destroyer. This is the final configuration of the vehicle.

Work on the Pz.Sfl.IVc died down and started up over and over again. The cause for this was Krupp's work on other projects. In addition, the military's ideas for the prospective SPG kept changing. First they demanded a quick chassis, then criticized the thin armour. Because of this indecision, the vehicle was still only a draft project by the summer of 1942.

Orders for chassis for an SPG with a 149 mm sFH 18 howitzer came in during the spring of 1942. It was called Geschutzwagen III/IV, and the SPG that used this chassis was better known as the Hummel. Further development of the chassis led to a tank destroyer with a gun with the ballistics of the 8.8 cm Flak 41. Rheinmetall-Borsig and Krupp received contracts for the development. The Pz.Sfl.IVc project was raised again. This time, work reached the creation of a full scale model. However, a quick SPG was once again not needed. The success of the Geschutzwagen III/IV platform played a large role. A decision was made to make two SPGs on one chassis, and thus the tank destroyer known as the Hornisse or Nashorn was born.

Quick fold-out AA gun

One of the reasons why the Pz.Sfl.IVc project did not die completely was that Krupp was designing it to handle several tasks at once. One of the variants was a medium SPG, armed with the same Flak 18. Unlike the tank destroyer role, the SPAAG role was unfilled. The Germans had a wheeled SPAAG on the Vomag chassis, built from a bus, and a halftrack on the Sd.Kfz.9 mount, but nothing fully tracked existed even in small batch production.

The 8.8 cm Flak 41, a powerful, but very heavy AA gun.

However, the Wehrmacht was in need of a medium SPAAG on a tracked chassis to escort tank units. In addition, a new AA gun was introduced, the 8.8 cm Flak 41. This was an exceptional gun, but its mass increased to 8 tons. The idea came up to create a self propelled gun mount to give this system more mobility. The Geschutzwagen III/IV platform was unusable for this task, as the layout of the chassis did not allow for a large platform that an AA gun requires. On the other hand, the Pz.Sfl.IVc was initially designed to provide a large platform. In addition, Rheinmetall was working on an analogous system on the Panther chassis.

Versuchsflakwagen at the Grusonwerk factory, December 1943.

Development of the SPAAG began in June of 1942 and continued alongside the development of the tank destroyer. The tank destroyer was being left behind the SPAAG variant. It is easy to notice that the variant with the Pak 43 was, essentially, just a mounting of the anti-tank gun on a platform clearly designed for the 8.8 cm Flak 41. This was one of the key reasons for its failure, since the concept proposed by Krupp was not met well by the Armaments Directorate. The situation became more comic as a short time later they did indeed request a "self propelled gun mount".

The same vehicle with folded out side shields and the gun at maximum elevation.

Mobility was key in the Pz.Sfl.IVc's design. The vehicle was equipped with the 360 hp Maybach HL 90 P engine. The same 9 L engine was proposed for the mass produced leFH 18 (Sfl.), which were known as the Pz.Sfl.IVb by the summer of 1942. The engine and other components were positioned to allow for a large platform that would let the gun rotate freely. Unlike the anti-tank variant, which had a flat floor in the rear part of the chassis, the SPAAG named VFW (Versuchsflakwagen, experimental AA gun vehicle) had a bulge that held the air intakes. During travel, the fighting compartment was flanked by large shields, which could be folded out to give a large fighting platform. This made the crew's job easier. 48 rounds of ammunition were stored underneath the floor.

Folding out the shields enlarged the platform.

The vehicle was equipped with the ZF SMG 90 gearbox and the Henschel L320C turning mechanism. Thanks to this, the SPG's top speed would have been 60 kph. It is not clear why a SPAAG with a high caliber gun would need such speed. Since Krupp was loaded with work on other topics, components from the new chassis were tested on PzIV tanks that were turned into mobile test labs. Two PzIV Ausf. E tanks were used to test the interleaved 700 mm road wheel running gear starting in the summer of 1942.

Another vehicle was used to test the ZF SMG 90 gearbox and the Henschel L320C turning mechanism. These trials continued until November and ended in failure. As a result, an alternative variant of the transmission with a Krupp turning mechanism and a SSG 76 gearbox, which was used on the PzIV, was chosen. This solution was chosen as a backup.

The side shields are half-raised.

British Bomber Command had a direct influence on the deadlines of the development of the Versuchsflakwagen. Bombing raids on Essen, where Krupp's manufacturing base was located, began in March of 1942, but ended shortly. However, in March of 1943 the city and its factories was subjected to two bombing raids that counted 400-450 aircraft each. Production plants were destroyed and significant damage was caused to the factory's design bureau.

Finally, 700 aircraft bombed Krupp's factories on the night of June 25th to June 26th. This raid, which ended the super-heavy Maus project, also damaged the Pz.Sfl.IVc. The assembly of the prototype had to be relocated to Grusonwerk in Magdeburg. Since the factory was very busy, the prototype was only finished in early November of 1943. Trials showed that the SMG 90 gearbox and L320C turning mechanisms did not work out. The reserve transmission design had to be used.

It was possible to traverse the gun without fully lowering the shields.

The transmission problems were among the simplest plaguing the vehicle. One of the biggest issues was the change in the concept for self propelled artillery. Experience in war showed that the most effective way to combat aircraft, especially in tank and mechanized units, was with lower caliber guns, specifically 37-55 mm autocannons. Heavy bombers that the Pz.Sfl.IVc was designed to combat were rarely the enemy of the Panzerwaffe. The tankers often encountered ground attack aircraft, against which 88 mm AA guns were not very effective.

On November 5th, 1943, engineer Klein from the AA directorate demanded that the second prototype be cancelled and its parts be scrapped. Speer, the armaments minister, put the final end to the development. In January of 1944 he ordered to cease work on the Pz.Sfl.IVc and other such projects. This direction was considered to be fruitless. This makes work of scale modellers depicting further evolutions of these systems on chassis up to the superheavy E-100 quite comical. Something that was deemed fruitless in early 1944 could not continue evolving until the end of the war.

A draft of the Versuchsflakwagen for the 8.8 cm Flak 37 gun.

The cessation of development did not mean that the Versuchsflakwagen would be scrapped too. Despite some transmission issues, the chassis was rather good and satisfied the requirements posed for it, including mobility. The top speed of 60 kph was reached during trials and could be sustained without overheating the engine. The average speed for the 26 ton vehicle was 40-50 kph depending on the road conditions. On their third try, Krupp managed to make a self propelled gun mount that was equal in mobility to the Pz.Sp.Wg.II Luchs. This vehicle could have been used for the Waffentrager program that was already launched at the time, but the German bureaucracy machine was already in action.

The Pz.Sfl.IVc in the 26th Tank Division.

Fortunately for the prototype chassis, it was not scrapped. Orders to convert the vehicle were given in March of 1944. The area of the air intakes was enlarged, likely as a result of the trials. The armament was also changed. the lighter an more compact 8.8 cm Flak 37 was installed. However, calculations showed that the mass remained at the same 26 tons.

The air intakes can be seen.

The vehicle retained most of its characteristics in this form. The crew consisted of nine men, seven of which rode in the fighting compartment during travel, and two (the driver and commander) in the driver's compartment. The ability to partially open the shields was also retained. This allowed the gun to fully rotate while still protecting the crew from flanking fire.

The crew during travel. The air intakes can be seen here too.

The converted SPAAG was sent to Italy in the summer of 1944. It was included in the 304th SPAAG Battalion. This unit was a very unusual addition to the 26th Tank Division. It was armed with the same 8,8cm Flak 37 (Sf.) auf s. Zgkw. 18t that the Pz.Sfl.IVc was supposed to replace. All 12 vehicles that were built on the Sd.Kfz.9 chassis were also used in the 304th battalion. Their unfortunate replacement also served here. The further fate of this vehicle is not known.

The crew's gear was attached straight to the shields.

The story of the Pz.Sfl.IVc is typical for German tank design. Work went on for five years and ended with nothing. The experience gained during the development was not needed. The rather good design of the chassis had no influence even on Krupp's designs. This scenario was hardly an exception.

An extra chassis

The Pz.Sfl.IVc was not the last B.W. type chassis designed by Krupp. The Waffentrager program, launched in the second half of 1942, required the creation of a whole family of light, heavy, and medium self propelled gun mounts. Experience in fighting on the Eastern Front showed that the halftracks that were used to tow heavy guns were in short supply. This often led to the loss of guns and their capture by the Red Army.

This issue was particularly painful in late 1942. New guns, including anti-tank guns, approached and then surpassed the Flak 18 in mass. This triggered the idea of creating a cheap SPG chassis. A high speed was not required, just 17 kph would be enough. Another requirement was the ability to use standard towed guns as armament, with the ability to remove them and install them on a towed mount.

Mittlerer Waffenträger für die 12,8 cm K 81 L/55, an anti-tank self propelled gun mount.

One of the first companies to start working on this program was Skoda. In August of 1942 it already proposed a lightened Pz.Kpfw. T-15 that could be equipped with a 105 mm leFH 18 howitzer or a 149 mm sFH 18 howitzer. As the project required, the gun could be fired at any traverse position. The guns could also be quickly mounted or removed. This project was quickly trampled, since fierce competition broke out in  the medium "weapon carrier" space.

The requirement for medium self propelled gun mounts changed by the end of 1942. The 128 mm Kanone 81 and 149 mm leFH 18 howitzer were now required as the armament. The 10 cm Kanone 18 and 8.8 cm Pak 43 were also listed, but the first system vanished from the list in the summer of 1943, and the second was moved to a lighter chassis.

The howitzer variant was named Mittlerer Waffenträger für die 15 cm sFH 18 L/29,5.

Work continued on three types of chassis: PzIV, GW III/IV, and Panther. In addition, Krupp designed some exotic hybrids. For example, the Grille 15 was introduced in March of 1943, which used a Panther hull, but a suspension that more closely resembled that of the Pz.Sfl.IVb: the PzIV's suspension with enlarged road wheels.

The Mittlerer Waffentrager on the PzIV chassis was ready by early 1944. Krupp produced a chassis with a front engine compartment that used the PzIV suspension almost with no changes. The gun was placed on a special pedestal mount, shifted towards the rear. The project could use one of two guns: 15 cm sFH 18 L/29,5 or 12,8 cm K 81 L/55. Unlike its speedy predecessor, not even a model was built of either of these vehicles.

A meeting was held at the  Steyr-Daimler-Puch HQ on February 4th, 1944. There, the 4th Department of the Armaments Directorate corrected its requirements for the Waffentrager. Now, special chassis were permitted, the bore axis height was reduced to 1800 mm, and the top speed increased to 35 kph. The armour thickness was 20 mm in the front and 10 mm along the sides. The ammunition capacity was 50 rounds, 20 of which should be held in ready racks. The PzIV and GW III/IV were removed from the list of potential vehicles. As for the Panther SPG, development continued until the summer of 1944, but did not progress past the creation of models.

Improvised SPAAG on the PzIV Ausf. H chassis captured at an airport in Pilsen in May of 1945.

The decision made on February 4th, 1944, was the finale of the five year long development of SPGs on the PzIV chassis, at least on the official level. It did not impede the creation of a vehicle that is absent from any official correspondence, but remains on photographs. In April-May of 1945,  American forces captured Pilsen, the city where Skoda's factory was located, in a rapid advance. The local airport had a repair yard, which contained one very strange vehicle. A PzIV Ausf. H without a turret platform was used to install an 8.8 cm Flak 37. It is hard to judge who created this vehicle and when. Likely, this was a field modernization.

It is sometimes claimed that that two such vehicles were found in Pilsen, but photographs do not confirm this fact. The Hummel that stood nearby is the likely cause of confusion. Even more confusing is the claim that three such vehicles were built. Likely, there is a mixup with the Pz.Sfl.IVc, as three of those were ordered (but just one built). The only thing that is known for sure is that such a vehicle definitely existed, unlike the similar photoshop with a T-34.

Original article by Yuri Pasholok.