Panzerkampfwagen I Ausf.B mit 7.5 cm StuK 40

German Reich (1945)
Improvised Self-Propelled Anti-Tank Gun – At Least One Built

In the final months of the war, the Germans were losing men and materials on all fronts. Out of desperation, all kinds of improvised vehicles, mostly based on obsolete vehicles or simply whatever was at hand, were rushed into service. One such vehicle was built using a Panzer I Ausf.B chassis on top of which a 7.5 cm StuK 40 was placed, for use in the futile defense of Berlin in 1945

History

By 1945, the German Army and its industry were in ruins. The Allied bombing campaigns, lack of resources, and the rapid advances of Germany’s enemies on their own soil made the production of new vehicles difficult. Despite this, the German war industry was desperately hanging on, producing limited quantities of new vehicles. By this point, these efforts were hopelessly insufficient to rearm the depleted German military formations. In desperation, some improvised vehicles were created by using all kinds of available chassis, ranging from experimental, obsolete, or even training vehicles, and adding whatever weapons were at hand.

Vehicles such as the Panzer I were reused in this manner, creating unusual and rare improvised fighting vehicles. The Panzer I Ausf.A and B were introduced as the first real German serially-produced tank in 1935. Even though it was obsolete by 1939, it still saw service throughout the war. After 1941, these were retired from service as combat tanks, but their chassis were reused for other purposes, mostly as training or ammunition supply roles. By 1945, their numbers were greatly diminished due to many factors, such as combat losses.

Using such a vehicle as an improvised fighting platform speaks for itself in regard to German desperation at this point. Thanks to a surviving photograph, we know that at least one Panzer I Ausf.B was modified by removing the turret and parts of the superstructure and adding a 7.5 cm StuK 40 gun taken from a StuG III. Who exactly built it and when is unknown. What is known is that it was used during the defense of Berlin in 1945.

Name

Given its improvised construction, this vehicle likely never received any form of proper designation. Possible designations such as 7.5 cm StuK 40 (Sf) auf Panzerkampfwagen I ohne Turm may have been used.This article will use Panzer I Ausf.B mit (English: with) 7.5 cm StuK 40 for the sake of simplicity.

Design

The overall design of this vehicle is unfortunately not documented in any sources. Based on the only known photograph, several educated guesses about its overall construction.

Hull

The Panzer I hull appears to have been left unchanged. Like all German tanks, it could be divided into three sections: the front part where the transmission was placed, the central crew compartment, and the rear-positioned engine. The overall construction was made out of several armor plates welded together, with a firewall separating the engine compartment and the crew compartment.

Suspension

The suspension is another element that remained unchanged. It consisted of five road wheels per side. The first wheel used a coil spring mount design with an elastic shock absorber in order to prevent any outward bending. The remaining four wheels were mounted in pairs on a suspension cradle with leaf spring units. There was a front drive sprocket, rear idler, and four small return rollers.

The Panzer I Ausf.B was never fully reliable, especially when the chassis was converted for other purposes, such as the 15 cm sIG 33 auf Panzerkampfwagen I ohne Aufbau (English: Without a superstructure). Given the added weight of the 15 cm sIG 33 gun, the suspension was very prone to malfunctions and breakdowns.

This was likely also the case with the 7.5 cm L/48 gun, as the weight and recoil force when firing would likely cause damage to the suspension, as its design was never intended to be able to resist such stress.

Engine

The Panzer I Ausf.B was powered by a water-cooled Maybach NL 38 Tr, which was able to supply 100 hp at 3,000 rpm. The maximum speed with this engine was 40 km/h and only 15 km/h cross-country. The added weight of the gun, ammunition, and likely additional crew members on the Panzer I Ausf.B mit 7.5 cm StuK 40 would have led to an overall weight increase of possibly up to 2 tonnes, if not more. This would greatly affect the engine’s overall performance, although to what extent is unknown. The standard Panzer I fuel load capacity was around 144 liters, which provided an operational range of up to 170 km. By 1945, fuel was a scarce commodity for the Germans, so regardless, it is unlikely that this vehicle ever received any large enough quantities of fuel to go anywhere besides its station point.

Superstructure

The superstructure of this vehicle received a series of modifications that were necessary in order to install the large gun. The upper armor and the turret were removed. Parts of the rear armor appear to have been slightly cut down.

Two interesting features can be noticed on the right side of the superstructure. Firstly, there is an unidentified round-shaped object that casts a shadow on the superstructure. It is possible that this was a seat added for the loader, although it could also simply be an extended plate to provide the loader with more working space. In front of it, a larger flat plate with a handle can be seen. It appears not to be an original part of the Panzer I, as it is on the side that did not have any hatch. This part could also be intended to be lowered and provide the loader with more working space. In either case, due to a lack of information, we cannot be sure. Interestingly, on top of the frontsuperstructure, a small shield was added to cover the space between the gun shield and the mount.

Armor

The armor of the Panzer I Ausf.A and B was quite thin. The Panzer I’s front hull armor ranged from 8 to 13 mm. The side armor was 13 mm, the bottom 5 mm, and the rear 13 mm. The armor was made of rolled homogenous hardened plates with a Brinell hardness of 850. It was welded and formed the body of the superstructure and hull. Whilst insufficient to protect against tank and anti-tank gunfire, this armor was still adequate to provide protection from enemy small arms.

The crew operating the gun was only protected by the gun shield. The armor thickness of it is unknown, but it was likely only a few millimeters thick. Given the small working space for the gun operator and the loader, both would be quite exposed to the enemy’s small arms fire. Light armor does not necessarily mean that the vehicle was useless, thanks to its gun it could still fire at great ranges and from well-selected positions.

On the other hand, this was neither 1942 nor 1943, when German guns had a huge advantage over Soviet armored vehicles. By 1945, the Soviets employed tanks such as the T-34-85 and the IS-2, which had enough firepower to deal with German Tiger and Panther tanks at a distance, so a lightly protected Panzer I was surely no problem for them. It is also noteworthy that as this vehicle was used in the defense of Berlin, combat action was likely to occur at close ranges, making this vehicle quite exposed.

Armament

The main armament of this modified vehicle was the 7.5 cm StuK 40 L/48 gun, which was probably taken from a damaged StuG III assault gun. This gun was developed by Krupp and Rheinmetall in 1942. It was initially used with a barrel length of L/43, although later that year it was increased to L/48. Both versions of the gun had a semi-automatic breech, which means that, after firing, the spent cartridge would be self-ejected, thus increasing the overall firing rate. It was fired electrically. When mounted on StuG III vehicles, the elevation of this gun went from –6° to +20°, while the traverse was 10° to either side. The elevation, depression, and traverse limits for this gun as mounted on the modified Panzer I are unknown.

Armor-piercing shells fired from this gun had a muzzle velocity of 790 m/s. The armor-piercing (Pz.Gr.39) round could penetrate 85 mm of armor (sloped at 30°) at 1 km. The maximum range of the high-explosive rounds was 3.3 km while, for armor-piercing, 1.4 to 2.3 km, depending on the type used. The gunner used the Selbstfahrlafetten Zielfernrohr Sfl.Z.F.1a gun sight to acquire direct targets. For indirect targets, on the other hand, either the Rundblickfernrohr 32 or 36 were used, which had a magnification of 5x and a field of view of 8°.

In order to install this gun on the Panzer I’s hull, some modifications were needed. First, a stable platform base had to be placed inside the hull. On top of it, the 7.5 cm StuK 40 L/48 with its mount was placed. The protective recoil cylinder mantlet was not used on this vehicle. Given the gun’s weight, the Germans added a large travel lock in front of the gun. The whole gun installation would take up most of the Panzer I’s interior, making room for spare ammunition difficult. The only possible location where the ammunition would have been located was atop of the engine compartment. A minor change to the gun was the lack of the spent cartridge bag.

Crew

Normally, a vehicle like this modified Panzer I would have needed at least three crew members to be fully effective. A driver located inside the vehicle would have been the only crew member fully protected by armor, a gunner who would possibly have also acted as the commander positioned to the left of the gun, and a loader positioned opposite the gunner. The two gun operators would have had quite limited space to effectively operate this vehicle. Based on the German’s lack of manpower by 1945, it is also probable that this vehicle may have had an even smaller crew of possibly two. This meant that these two had to perform other tasks too, in addition to their original ones.

Was the Panzer I Ausf.B mit 7.5 cm StuK 40 Used in Combat?

Nothing is known about the history of this vehicle. Based on the available photograph, we can assume that it was modified in and saw service in Berlin. A detail that helps us identify where the photo of the Panzer I Ausf.B mit 7.5 cm StuK 40 was taken is the command tower that can be seen in the background. Berlin was defended by three immense Flakturme (English: Flak towers): Flakturm Humboldhain, Flakturm Tiergarten, and Volkspark Friedrichshain. These were basically massive, reinforced concrete bunkers equipped with several larger-caliber anti-aircraft guns. Each gun tower was provided with more minor but still huge command towers. Their purpose was to relay information about enemy air activity.

Flakturm Humboldhain was placed on a small hill that does not appear in the photograph, so it can be excluded. The command tower for ‘Zoo-bunker’ lacked some features, such as the four round-shaped concrete platforms located on the tower’s top, that the tower in the picture has. The most probable explanation is that the tower in the background belongs to the Volkspark Friedrichshain tower. The design of the command tower is similar and also there are buildings to the left of the Panzer I’s position which match those in the photo.

The missing track links may indicate that this vehicle was not fully operational and was instead towed to its defense point. Given that the picture of it was taken in an open space and the Panzer I Ausf.B mit 7.5 cm StuK 40’s weak protection, this would be an illogical thing to do. It is possible that by the time the photograph was taken, it was already in the process of being salvaged for scrap. On the other hand, it may have been in the process of being towed before being abandoned in a rush.

Another possibility is that this vehicle was at some point converted to this gun configuration to be used as a training vehicle with the gun not actually intended to be fired. While this at first seems logical, given the weight of the gun which would have put too much stress on the chassis, this seems highly unlikely.

In any case, the fate of this vehicle is unknown, but it was likely scrapped after the war by the Soviets.

Conclusion

Placing a large gun such as the 7,5 cm StuK 40 on a chassis weak and prone to malfunctions difficult to understand. Even in desperation, whoever built it must have known that the recoil force of the gun was simply too much for the Panzer I’s chassis to handle. Firing could have easily led to the breakdown of some components of the suspension or the engine. Armor protection was almost non-existent. Even using it as a static emplacement would be suicidal, as the vehicle’s height would not have allowed for it to be easily camouflaged.

Panzer I Ausf.B mit 7.5 cm StuK 40 Technical specification
Crew	3 (commander/gunner, loader, and driver)
Engine	Maybach NL 38 TL 6-cylinder water-cooled petrol
Speed	40 km/h, 15 km/h (cross-country)
Range	170 km
Primary Armament	7.5 cm StuK 40

Sources

D. Doyle (2005). German military Vehicles, Krause Publications.
D. Nešić, (2008), Naoružanje Drugog Svetsko Rata-Nemačka, Beograd
Walter J. Spielberger (1993) Sturmgeschütz and its Variants, Schiffer Publishing Ltd.
T. Anderson (2016) Sturmartillerie Spierhead Of the Infantry, Osprey Publishing
P. Chamberlain and H. Doyle (1978) Encyclopedia of German Tanks of World War Two – Revised Edition, Arms and Armor press.
Ian V. Hogg (1975) German Artillery of World War Two, Purnell Book Services Ltd
T.L. Jentz and H.L. Doyle Panzer Tracts No.1-1 Panzerkampfwagen I