Gepanzerte Selbstfahrlafette für 7.5 cm L/41 Sturmgeschütz (Sturmgeschütz III L/41)

German Reich (1941)
Self-Propelled Assault Gun – At Least 1 Prototype Built

During the battles across the Soviet Union and North Africa in 1941, the Germans were hard-pressed as their anti-tank and tank guns proved to be almost useless. In desperation, the Germans often employed the 8.8 cm anti-aircraft or even some larger caliber artillery gun as makeshift anti-tank weapons. German tanks and armored vehicles, such as the StuG III series, lacked the firepower to reliably pierce the armor of enemy tanks. In 1942, the improved 7.5 cm L/43 and L/48 guns were introduced into service, and, thanks to them, the Germans finally had the means to effectively fight back. The development of such weapons had actually been initiated before the start of the war by the Krupp firm. This gun would be fitted into at least one heavily modified StuG III vehicle.

A Brief History of German Early 7.5 cm Gun Development

During the mid-1930s the Heereswaffenamt HWa (English: Army Weapons Department) issued a request for the development of two new types of tanks designed to fulfill specialized combat roles. Both received somewhat unusual designations but this was done intentionally to deceive the Western Allies, as the Germans were still technically forbidden to develop such vehicles by the Treaty of Versailles.

The first one was the Zugführerwagen ZW (English: platoon commander’s vehicle). This vehicle armed with a 3.7 cm KwK (short for ‘Kampfwagenkanone’ which could be translated as ‘combat vehicle cannon’ or, more simply, as ‘tank gun’) L/45 gun was intended to spearhead an attack on German armored formation and deal with enemy armor. It would eventually evolve into the Panzer III series.

The second, known as Begleitwagen BW (English: escort vehicle), was intended as a firing support vehicle. Its purpose was to deal with enemy fortified positions, anti-tank and artillery emplacement, and similar targets by firing high-explosive ammunition. While the 3.7 cm gun was a good weapon for the pre-war standards, it lacked sufficient destruction and firepower. That is why the Germans decided to use the 7.5 cm KwK 37 L/24 gun as the main armament for this vehicle. This would lead to the creation of the Panzer IVs series.

This 7.5 cm gun was not a new design and was already used on several early and experimental German tanks, such as the Grosstraktor (English: large tractor) and Neubaufahrzeug (English: new vehicle) projects. While these were unsuccessful, they provided the Germans with vital experience in tank design.

The 7.5 cm KwK 37 L/24 had a short barrel that had 28 grooves, each 0.85 mm deep. It had a semi-automatic breech, which means that, after firing, the spent cartridge would be self-ejected, thus increasing the overall firing rate. The gun recoil cylinders that stood outside of the turret and the gun were covered by a steel jacket and a deflector guard. For the gunner’s protection, a recoil shield was added to the rear of the gun. Usually, the gun was provided with a ‘Y’ shaped metal rod antenna guide placed under the gun. Its purpose was to deflect the antenna and thus avoid damaging it during turret rotation.

Initially, this gun could fire a few different types of ammunition. These include the 7.5cm GrPatr 34 high-explosive, 7.5 cm PzGr patr anti-tank, and NbGrPatr smoke round. Given its original purpose, the early Panzer IV would mostly be supplied with the high-explosive round. This round had a weight of 5.7 kg and with a muzzle velocity of 420 m/s could reach a maximum distance of 6.5 km. The anti-tank round was heavier at 6.8 kg, but had a lower velocity of 385 m/s, and could pierce around 39 mm of 30° angled armor at distances of 500 m. The 7.5 NbGr Patr was a smoke-screen round. When fired, it would create a smoke cloud that could cover an area of 15 to 20 m for a period of some 30 seconds.

A New Sturmgeschütz III Vehicle

Based on the combat experience of the German Army during the First World War, Erich von Manstein proposed the introduction of a highly mobile, well-protected, and well-armed self-propelled artillery gun. Such vehicles were meant to provide infantry with mobile close-fire support during combat operations. Thanks to the self-propelled chassis, these could be quickly redeployed to respond to any new threat. This self-propelled artillery gun was to be an organic part of standard infantry divisions. Such a vehicle known as Sturmgeschütz III or simply StuG III (English: Assault gun) was developed just prior to the war in the West in May 1940. It quickly proved to be an effective concept and the German Army requested that its production be increased.

The StuG III basically consisted of a Panzer III chassis which was combined with a new superstructure armed with the 7.5 cm StuK 37 (Sturmkanone – assault gun) L/24 gun. It was more or less a copy of the Panzer IV’s 7.5 cm KwK 37 gun just adopted for use inside the StuG III. With this gun and strong armor, the StuG III became a very effective and popular vehicle in the German arsenal. It was able to provide mobile firepower to German infantry formations.

Combat Experiences

During the Polish campaign of September 1939, the 7.5 cm proved to be more than much of the enemy armor and fortified positions. In a 3rd Panzer Division’s officer’s report, the performance of the 7.5 cm gun was described as follows.

“ .. Once again it has been made obvious that Panzer units should avoid combat in forests and most towns. However, those with houses built from wood were easily set on fire with high-explosive rounds fired from 7.5cm-armed PzKpfw. The subsequent blaze would force any Polish troops out into open, where we shot them down with our machine gun fire. I am convinced that the 7.5cm-armed PzKpfw is the perfect support vehicle for infantry in urban warfare… “

For the anticipated war with the Western Allies, and especially France, the Germans could count on less than 300 Panzer IVs and a small number of StuG IIIs equipped with the 7.5 cm gun. Prior to the war, the Germans were clearly aware of the new French tank designs. When developing the 7.5 cm gun, they also introduced armor-piercing ammunition specially designed to deal with the French armor. This could be seen in a report made by the Waffenamt (English: Ordnance Office) written on 30th October 1935.

“ …. When firing the 7.5cm Panzergranate [anti-tank] 43mm of armour was penetrated at an angle of 60 degrees which makes it eminently suitable for defeating the new French tank type. However, these are theoretical considerations which will have to be proven by practical trials at Putlos; the low muzzle velocity results in a curved trajectory which will seriously affect accuracy. Despite this, we expect the BW [Panzer IV] to defeat all types of French tanks with the exception of the Char 2C super heavy tank. ….”.

The effectiveness of the 7.5 cm gun against enemy armor can be seen during the battles around Stonne in France in mid-May 1940. One Panzer IV managed to destroy 2 Hotchkiss H39 tanks but failed to do anything against the heavy Char B1 Bis tank despite firing 20 or so rounds against it. Although the rounds could not penetrate the heavy French armor, the Panzer IV did manage to destroy the French tank’s track and thereby render it immobile. At the same time, a second B1 Bis was engaged by the Panzer IV. This time, due to a lucky hit, the German tank jammed the second French tank’s cupola. The Panzer IV managed to fire another round to the rear, and this time the 7.5 cm gun managed to penetrate the armor of the B1 Bis which was blown up by an internal explosion. The Char B1 and the British Matilda Mk.II were tanks that the German intelligence failed to detect, which were almost immune to German weapons.

Despite facing such strong opponents, the Germans did little in regard to improving the firepower of their tanks. The Panzer III’s 3.7 cm gun would be replaced with a short barrel 5 cm caliber gun, while the armament on the Panzer IV and StuG III would remain the same. In 1941, when the Axis forces invaded the Soviet Union, the 7.5 cm gun proved more than sufficient in dealing with the light enemy armor, such as the T-26 and BT-series. However, once the stronger T-34 and KV-series were encountered, the effectiveness of the 7.5 cm armor-piercing round was shown to be lacking. The high-explosive round, on the other hand, was somewhat more successful. While it could not penetrate the thick armor of the enemy tanks, its explosive firepower was enough to cause serious damage to them by blowing up the suspension or even jamming the gun. By late 1941, due to the ineffectiveness of their anti-tank guns, the Germans were becoming desperate to find a solution. The introduction of tungsten-based ammunition was seen as a simple solution. The downside of it was that Germany was in short supply of this metal. Interestingly, due to the 7.5 cm L/24’s low velocity, the Germans never developed a tungsten round for this gun.

In December 1941, Adolf Hitler issued an order that the production of the shaped-charge round should begin as soon as possible. This led to the introduction of the 7.5 cm GrPatr38 shaped-charge rounds. These had a velocity of 450 m/s with the difference that the later version had a slightly better penetration of 7.5 cm at any range. While on paper this meant that any enemy tank could be defeated, the reality was quite different. For example, the low velocity led to a rather limited accuracy. In addition, the overall ballistic design of this round was far from perfect as it too often simply bounced off or failed to penetrate enemy armor. Improving the anti-tank performance of standard armor-piercing rounds was thus seen as the most preferable solution, The easiest way to do so was to increase the round propellant charge and use a longer barrel, thus increasing velocity. While this project was initiated in late 1941, the firm of Krupp had already considered this problem back in 1938.

Krupp 7.5 cm L/41 Gun

With the slow development of the new StuG III vehicles, new designs and ideas were often proposed to further increase their effectiveness. One of these included a proposal for a new so-called Verstärktes (English: improved or enhanced) StuG III vehicle. It was to be armed with a much longer 7.5 cm gun. Unfortunately, this part of StuG III development is rather obscure and not well documented in sources, where it is rarely mentioned.

However, what is clear is that this gun was intended to have improved anti-tank performance thanks to improved velocity. It might appear odd that a high-velocity gun was not considered earlier, but it must be borne in mind that the primary role of the StuG III was to engage fortified positions, not tanks. Combat versus tanks was to be done only in case of emergency or self-defense. It is also possible that the Germans wanted simply to improve the StuG III’s overall firepower but also to increase the designated task that such a vehicle was to perform.

In either case, in August 1938, the Waffenamt Prüf 4 (English: Army Weapons Agency of the Artillery Branch) instructed both the Rheinmetall-Borsig and Krupp firms to begin preparation for developing such guns. Another quite interesting and also confusing fact is that the Panzer IV was not included in this project despite using the same gun as the StuG III and could also benefit from using the stronger armament. On 3rd November, Krupp informed Waffenamt Prüf 4 that their project received the 7.5cm L/41 (sometimes referred to as L/40) sPaK verstärkt (English: improved or strengthened) designation. A month later, the WaPrüf 1 (English: Army Weapons Agency of the Ammunition Branch) asked Krupp to make the first drawing of the ammunition that would be used on this gun (armor-piercing and high-explosive). In early 1939, the first gun prototypes were to be completed and issued for firing trials, but delays occurred which postponed these trials.

In April 1940, firing test trials were held at Meppen. These showed some problems with spent cartridge ejection. In addition, it was requested to add a muzzle brake to the gun to reduce recoil forces. On 7th May 1940, after more firing trials were conducted, the ejection problem was noted to still be present. On the other hand, the new muzzle brake was noted to be highly successful, reducing the recoil by some 47%. In the following firing trials, some 130 rounds of ammunition were used. An average velocity of 675 m/s was achieved. Only one ejection problem was noted. Unfortunately, it appears that no photograph of this gun is known to have survived.

Into a StuG III

As the gun was being tested, several (the precise number is unknown) modified and experimental StuG III vehicles were being built using Panzer III Ausf.F chassis. It is not clear when this was initiated, by who, or who actually designed and built the vehicle. Likely many different firms and companies would have been involved in this project before the vehicle was assembled at Daimler-Benz. This company was closely engaged in the early StuG III’s development and production. Sometime in May 1940 (or even earlier), this vehicle was transported to the Jüterbog artillery training center for further evaluation.

Name

The standard production vehicles received the Gepanzerte Selbstfahrlafette für Sturmgeschütz 7.5 cm Kanone Ausführung with a capital letter depending on the version. If these Versuchsfahrzeuge (English: experimental or test vehicles) received any official designation it is sadly unknown. A possible designation using the previous example could have been Gepanzerte Selbstfahrlafette für 7.5 cm L/41 Sturmgeschütz but this is speculation at best. For the sake of simplicity, this article refers to it as the 7.5 cm L/41 StuG III.

Design

The overall design of this vehicle is unfortunately not documented in the sources. Luckily, there are a few known photographs of it. Thanks to it, we can make several educated guesses about its overall construction. In addition, we know that they used the chassis taken from the Panzer III Ausf.F which was used for early StuG III vehicles.

Hull

The 7.5 cm L/41 StuG III hull would have consisted of three major sections. These were the forward-mounted transmission, central crew compartment, and rear engine compartment. The front hull was where the transmission and steering systems were placed and it was protected with an angled armor plate. The two square-shaped, two-part hatch brake inspection doors were located on the front hull.

Suspension and Running Gear

The 7.5 cm L/41 StuG III’s suspension consisted of six pairs of road wheels on each side. These were suspended using a combination of individual swing axles together with torsion bars which were placed in the bottom of the hull. The upper movement of each wheel’s swingarm was limited by contact blocks covered in rubber. Additionally, the first and the last wheels were equipped with a hydraulic shock absorber. At the front, there was a 360 mm wide 21-tooth drive sprocket. On the back of the hull was the idler with an adjustable crank arm. The number of return rollers was three per side. The whole suspension unit was taken directly from the Panzer III Ausf.F version.

The Engine

Given that the 7.5 cm L/41 StuG III was based on the Panzer III Ausf.F, it would have used the twelve-cylinder, water-cooled Maybach HL 120 TRM engine giving 265 hp at 2,600 rpm. With this engine the production version of the StuG III Ausf.A could achieve a maximum speed of 40 km/h, while the cross-country speed was reduced to 20 km/h. The fuel load of 310 liters was stored in two fuel tanks placed below the radiators in the engine compartment. With this fuel load, StuG III Ausf.A’s operational range was 160 km on roads and 100 km cross-country.

Given the added weight of the gun, ammunition, and armor, the 7.5 cm L/41 StuG III’s overall drive performance would likely (while not significantly) be still slightly reduced. To what extent it is impossible to know precisely due to lack of information.

The Superstructure

The superstructure was in many regards quite different from the standard StuG III’s superstructure. Due to the larger size of the ammunition, it was necessary to enlarge the whole superstructure. The most obvious change was extending the sides of this new superstructure. This provided additional working room for the crew but likely at the same time increased the ammunition load. The extended sides design was quite simple, which was built using flat plates.

The front driver’s (and opposite of him) angled plates were also redesigned. These were placed at a much higher angle providing better protection and removing the shot trap that the production StuG III had. This feature would be finally introduced to standard StuG III vehicles only in late 1942 starting from the Ausf.F/8 version. Another unusual feature was adding a driver visor port, on the right side of the front plate. The top armor was mostly flat, with the sides slightly angled toward the fenders. The three hatches for the gunner, commander, and the gunner would likely remain the same. The rear of the superstructure was completely flat which greatly simplified the overall design.

Armor Protection

The 7.5 cm L/41 StuG III vehicles received mild steel superstructure as they were intended for experimentation and evaluation. If accepted for service, the armor thickness would likely be the same as other StuG IIIs produced at that time.

The front and upper hull armor were 50 mm thick, while the sides and rear were 30 mm thick. The front superstructure armor plates were 50 mm thick. Like the hull armor, the superstructure side and rear were also 30 mm thick. The top armor was 10 mm, while the top of the engine compartment was slightly thicker, at 16 mm.

From August 1938 on, nearly all German panzers were equipped with a Nebelkerzenabwurfvorrichtung (smoke grenade rack system). This device was placed on the rear of the hull. It contained five grenades which were fired through a wired system by the commander. When activated, the StuG would then drive back under the safety of the smokescreen.

Armament

The main armament for this experimental vehicle was the Krupp 7.5 cm L/41 gun. Its overall performance is not well documented. According to Krupp documentation dated 15th April 1941, this gun had the following properties: it could fire a 6.8 kg round at a muzzle velocity of 670 m/s, its barrel length was 3,023 mm and its total weight was 1,400 kg. It was estimated that at ranges of 400 m this gun could penetrate 70 mm of armor plate at a 30º angle. Given its stronger recoil force, the gun would receive much larger recoil cylinders that were placed above the gun barrel. It was protected by an armored casing quite different from early and later production StuG III vehicles. To further reduce the recoil force, a double-baffle muzzle brake was used. The ammunition load is unknown, but given the enlarged superstructure, probably more than the standard 44 rounds. No secondary defense armament appears to be intended for this vehicle. This may have just been because this was an experimental vehicle.

Crew

The crew of this vehicle consisted of four: commander, driver, loader, and gunner. While the loader was positioned to the right of the gun, the remaining crew was placed opposite of him. The driver was positioned on the left front side of the hull. Just behind him was the gunner, and right behind him was the commander.

The Fate of the Krupp Gun

Following its completion, the prototype vehicle was sent to the Jüterbog artillery training center and later to Kummersdorf. In both locations, the gun was thoroughly examined and fire tested. On 19th March, it was transported to Daimler-Benz. At the end of the month, it was presented to Adolf Hitler. While it is unclear how this inspection went, Hitler was probably satisfied with the design as troop trials were ordered. If these proved to be successful, mass production was estimated to begin in spring 1941 or 1942 (sources disagree here). Nothing is known about these trials and if any problems with this vehicle were detected. Unfortunately, what happened to the Krupp L/41 armed StuG III vehicle is also unknown. Interestingly, in early November 1941, Krupp was informed that this gun was purely intended for the German Army and not to be exported to other countries. On 20th November, Krupp was informed that this project was to be canceled and any further work on it should stop. The prototype vehicle was likely rebuilt back to its original Panzer III configuration or reused as a training vehicle but its final fate remains unknown.

However, there may be some clue that one such vehicle may have seen combat action. But due to a lack of more information, this could not be confirmed with great certainty. During battles in Crimea in May 1942 between the Germans and the Soviets the 22nd Panzer Division and 197th Assault Battalion saw extensive action. Due to the lack of infantry anti-tank guns, the StuG III was used in anti-tank roles. The German armored formations managed to take out 250 Soviet tanks with the loss of only 3 StuG IIIs and 8 Panzers. In the after-combat report of the 197th Battalion, the use of 7.5 cm L/41 guns is mentioned. This may have referred to the Krupp prototype but it is impossible to confirm with certainty as it could also be just a simple typo by the author of this after-combat report.

While the 7.5 cm L/41 StuG III project was canceled, Krupp’s work on this gun was not completely wasted. In parallel to Krupp’s work, Rheinmetall-Borsig was also working on a similar project. This company was focusing on developing an anti-tank weapon which was basically an enlarged version of the 5 cm PaK 38. They succeeded in this, creating the 7.5 cm PaK 40 L/46 anti-tank gun. It would prove to be an effective tank destroyer and would see service up to the end of the war. This weapon was the main reason why the Krupp 7.5 cm L/41 gun project was canceled as the Rheinmetall-Borsig had better anti-tank power. This gun could on the other hand not be directly installed on StuG III and Panzer IV without a series of modifications. The main issue was the cramped interior of these two vehicles, in which their crews could not effectively use the PaK 40 long ammunition rounds. The Waffenamt Prüf 4 instructed Krupp and Rheinmetall-Borsig to join together to resolve this issue. These two firms resolved this problem with a simple solution. The Rheinmetall-Borsig barrel (albeit shortened to L/43 to reduce the cost and time needed for production) was merged with the Krupp-developed breech and cartridge chamber. This enabled the use of shorter but thicker ammunition rounds without any major loss of anti-tank properties. This led to the creation of the 7.5 cm Kanone 44 L/46 later in March 1942, renamed to 7.5 cm StuK (Sturmkanone) 40 L/43 gun.

This gun would be installed inside modified StuG III Ausf.E vehicles for testing held during April 1942. Regarding the vehicle design, it necessitated only some minor changes to StuG III Ausf.E’s original form. These mainly involved adding new ammunition racks, improving the ventilators, and some other minor changes. But besides that, the StuG III proved to be an excellent base for this gun. With this armament, the StuG III would become one of the best anti-armor vehicles in the German arsenal up to the end of the war.

Conclusion

The Krupp 7.5 cm L/41 gun was a huge missed opportunity for the Germans to develop a potent anti-armor gun even before the war. It appears that despite having the better overall performance of the short 7.5 cm L/24, Krupp’s own gun development ran at a relatively slow pace until it was eventually canceled in 1941. While having batter armor-piercing performance, it was not without problems, ejection of spent cartridges was a big problem, although that in time would likely have been resolved. The 7.5 cm L/41 gun (at least some part of it) would prove instrumental for the development of new series of the 7.5 cm L/43 and L/48 guns which finally gave the Germans the much-needed firepower, albeit too late.

Gepanzerte Selbstfahrlafette für 7.5 cm L/41 Sturmgeschütz Technical specification
Crew	4 (commander, gunner, loader, and driver)
Dimensions	Length 5.38 m, Width 2.92 m, Height 1.95 m
Engine	Maybach 120 TRM 265 hp @ 200 rpm
Speed	40 km/h, 20 km/h (cross-country)
Range	140 km, 85 km (cross-country)
Primary Armament	7.5 cm L/41

Sources

T. Anderson (2021) Panzer IV, Osprey Publishing
D. Doyle (2005). German military Vehicles, Krause Publications.
Walter J. Spielberger (1993) Sturmgeschütz and its Variants, Schiffer Publishing Ltd.
T.L. Jentz and H.L. Doyle (1999) Panzer Tracts No.8 Sturmgeschütz
P. Chamberlain and H. Doyle (1978) Encyclopedia of German Tanks of World War Two – Revised Edition, Arms and Armor press.
T. Anderson (2016) Sturmartillerie Spearhead Of the Infantry, Osprey Publishing
T. Anderson (2017) Sturmgeschütz Panzer, Panzerjäger, waffen-SS and Luftwaffe Units 1943-45 , Osprey Publishing
Walter J. Spielberger (1993) Sturmgeschütz and its Variants, Schiffer Publishing Ltd.
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