The “10.5 cm K (gp.Sfl.)” (Eng. 10.5 cm cannon (armored self-propelled gun)) or “10 cm K. Pz.Sfl.IVa” (Eng. 10 cm cannon self-propelled gun IVa), more commonly known as the “Dicker Max” (Eng. Fat Max), was a German self-propelled artillery gun. Development started in 1939, with the Army requesting a mobile “bunker buster” to destroy the fortifications on the French border. However, it would never fulfill that role, since the only two vehicles ever built were completed in early 1941, well after the end of the Battle of France.
The tank was based on the reliable Panzer IV chassis and used the standard K.18 German heavy artillery gun. The ammunition used consisted of Tungsten core rounds, which, in combination with the high velocity of the gun, had great penetration capabilities. Both vehicles were sent to the Eastern Front as tank destroyers, where one of the two would prove itself very successful, destroying a large number of Soviet tanks.
Context: The Need for a “Bunker Buster”
One of the main problems that the German High Command faced during preparation and planning for what would become the Second World War was how to defeat France. The German-French border was heavily fortified on both sides, with the French Maginot Line in the Alsace-Lorraine province and the German Siegfried Line mirroring it. In the end, two plans were prepared. The first plan was to revisit the Schlieffenplan that was already used during WW1. The idea was to invade the neutral Benelux states and invade France through the Belgian border.
The second plan was to power through the heavily fortified Maginot Line on the French-German border. However, this plan was only to be executed if the first plan failed. For this purpose alone, Germany started development of multiple heavy mortars, such as the 60 cm heavy mortar Gerät 40/41.
Beside this immense self propelled mortar, the Germans also intended to reuse the 8.8 cm Flak gun in this role. This gun was quite cumbersome to move, and in order to increase its mobility, two different proposals would be adopted.
The first would be created by placing the gun on a half-track chassis, creating the 8.8 cm Flak 18 Sfl. auf schwere Zugkraftwagen 12 t (Sd.Kfz.8) als Fahrgestell. The second variant was more orthodox in design, consisting of an armored half-track prime mover and a slightly modified 8.8 cm Flak 18 gun.
Both of these were built in limited numbers and saw use in their designated roles. Alongside the previously mentioned projects, the need arose for a much more compact self-propelled tracked chassis mounting a powerful gun that could deal with enemy concrete bunkers.
Development of the ‘Panzerselbstfahrlafette IVa’
Because Krupp had previously developed most German tanks, the Wa Prüf 6 (Eng. Army Design Office 6) once again contacted the firm in 1938. However, because Krupp had never designed a large caliber self-propelled gun, there were many different concepts and ideas on how this SPG would look. After having agreed on some specifications, Krupp started the development in 1939.
One of the first problems that occurred was where to place the engine. Krupp submitted two drawings in April 1939. In the first drawing, the engine was placed under the gun, in the front, which resulted in a shorter overhang, reduced by 800 mm compared to the second drawing, in which the engine was placed in the center. However, putting the engine below the gun resulted in numerous disadvantages that Krupp listed:
- poor access to the engine
- unfavorable installation of the radiator and cooling air fans
- crew encumbered by heat and fumes
- noise from the engine
- complicated operation of the transmission
- firing height increased to at least 2 m
- nose-heavy vehicle
On the other hand, placing the engine in the center of the hull would result in a lower firing height of 1.7 m and easier access to the engine. Additionally, the center of gravity would be better placed. In the end, the Wa Prüf 6 went with the first plan, because they thought that 800 mm of additional overhang with the second engine location was too much to handle for such an SPG.
Next, it was settled that a 180 hp V-6 engine would be installed instead of a 320 hp V-12 engine. However, the drawbacks were an increased height of 100 mm. By May 1939, Krupp had to design a new variant of the SPG with the engine below the gun, a torsion bar suspension, and a 6-cylinder engine. On May 2nd, 1939, Krupp presented their new design. This design included the V-12 Maybach HL 120 engine instead of the agreed V-6, because they thought the V-6 would not be powerful enough.
Additionally, it offered easier access to the cylinders. The problem was that the V-12 was heavier and was planned to go out of production. In addition, Krupp proposed that they would use the steering unit and transmission of the VK9.01, but with dry-pin tracks and not lubricated ones. Lastly, a muzzle brake was installed. This reduced the recoil from 1,000 mm to 800 mm, which meant the gun could be moved 200 mm more to the rear. It was also specified at this point that the 10.5 cm K 18 gun was to be installed in the new SPG.
On May 15th, 1939, Krupp again met up with the representatives of the Wa Prüf 6, who decided in favor of a new design with a 200 hp Maybach HL 66 placed in the middle of the hull, with an estimated total weight of 22 tonnes. Krupp added a radiator behind the engine for better cooling. Additionally, the Wa Prüf 6 requested the recoil cylinder and recuperator be moved back to save space in the armored housing. It was also at this point that it was settled that a regular panoramic gunsight was to be used for indirect firing and a new periscope gunsight would be added for direct firing. After this, approval for constructing a full-scale wooden mock-up model was given to Krupp.
Later, Krupp would inform the Wa Prüf 6 that a weight increase could not be avoided if they intended to use a torsion bar suspension. Because of this, Krupp suggested using the Panzer IV’s leaf spring suspension to save weight. This caused a problem, as the Wa Prüf 6 had originally planned to use the torsion bar interleaved suspension with lubricated tracks with rubber pads to achieve the maximum possible speed. However, the Design Office knew that the excess weight that came with the torsion bar suspension could not be reduced from anywhere else and that, due to this excess weight, lubricated tracks without rubber pads would not work due to ground pressure limitations. The Wa Prüf 6 then thought about simply using a regular torsion bar suspension with dry pin tracks, like on the Panzer II Ausf.D1/2.
On August 10th, 1939, when the wooden mock-up model was completed, Wa Prüf 6 suggested reducing the hull width to match the one of the Panzer IV. Later, the final decision was made to limit the weight to 20 tonnes by using the 8-wheel leaf suspension and chassis of the Panzer IV. The Panzer IV was chosen over the Panzer III because, at that time, it was more readily available and lighter.
On August 21st, 1939, the decision was made to use the Maybach HL 66 P engine together with the transmission and steering unit of the VK9.02, after previously being proven to be compatible. This was very important, because higher turning power was needed, as the Panzer IV normally had a width to length ratio of 1:1.46 compared to 1:1 for the VK9.02. A maximum speed of 35 km/h was requested.
Krupp was then awarded a contract to produce two trial vehicles, with all necessary equipment and real armor. The gun was to be provided by the Wa Prüf 4 (Department for Artillery). On September 4th, 1939, Krupp presented the construction drawings. The SPG did not have a turret and the hull and superstructure were constructed as one unit. The two trial vehicles were to be completed by May and June 1940, with the armor hulls completed eight weeks prior so the gun could be mounted in time.
On the same day, the final changes before production were made. These included minor changes to the gun sights, mounts for the periscopes, changes to the gun shield, and the gunner’s hatch being made to be rectangular and counter sunk. Additionally, the range finder was omitted.
The designation for the “10.5 cm K (gp.Sfl.)” is quite complicated. First off, this article is referring to the vehicle as an SPG, because that was its original intended role, even though it was eventually used and classified as a tank destroyer.
During the entirety of the development and production, it was referred to as “10 cm K. Pz.Sfl.IVa”, which stands for “10 cm Kanone Panzer Selbstfahrlafette IVa” (Eng. 10 cm canon self-propelled gun IVa). On August 13th, 1941, the name was changed to “10.5 cm K (gp.Sfl.)” which stands for 10.5 cm Kanone (gepanzerte Selbstfahrlafette) (Eng. 10.5 cm canon (armored self-propelled gun)). After the war, the name “Dicker Max” appeared, which is nowadays the most popular name for the vehicle, presumably due to its simplicity and funny connotations.
Interestingly, in a diary entry of the commander of the second SPG, Kurt Hildebrandt, he gives the vehicle’s nickname as “Brummbär”.
The article iwill use the original designation when referring to the development/production/design sections and the second description when referring to everything after August 1941.
During production, on October 11th, 1939, Wa Prüf 6 again met up with Krupp. They informed Krupp that the transmission of the VK9.02 would not be installed and the regular SSG 46 transmission should be used instead. However, this significantly reduced the speed to 25 km/h, as the gear ratio was only 1:8 at 188 hp.
During a production report in April 1940, Krupp stated that they were working on the next generation of AFVs, which included the “10 cm K. Pz.Sfl.IVa”. The completion date was extended to August 1940, since the need for such an SPG was reduced after the invasion of France, as the Germans attacked around the heavy fortifications of the Maginot Line. However, Krupp would only complete the two SPGs in January 1941. During a demonstration for Hitler on March 31st, 1941, it was decided that serial production could begin in spring 1942. However, this was never implemented and only the two AFVs were ever produced.
The 10.5 cm K (gp.Sfl.)’s hull was slightly redesigned in comparison to a standard Panzer IV hull. The forward-mounted transmission was unchanged. The difference was that it received a new angled top armor plate cover that completely enclosed it. The two hull frontal brake access hatches, including the large square-shaped bolted hatch, were retained. The engine and driver’s positions were moved to the center of the hull. The gun and its mount were placed directly above the enclosed engine. Lastly, to the rear, was the crew fighting compartment.
Given that this vehicle was based on a Panzer IV chassis (unspecified version, but likely the Ausf.D or E), it used the same suspension. This consisted of eight small double wheels placed on each side, suspended in pairs, and placed on four bogie assemblies. The small road wheels were suspended by leaf-spring units. There were also four return rollers on each side. Finally, the drive sprocket was at the front and the idler at the rear.
The suspension was to be taken from the Panzer IV Ausf.E, while the drive sprocket appear to be taken from Ausf.D. The difference was in the covering caps. This basically changed nothing, as these were only minor mostly changes and performed the same. It also does not help that the Germans often mixed older and newer components on their vehicles.
In its early development phase, Wa Prüf. 6 and Krupp engineers often discussed what type of suspension to use. Several different proposals were made. This included the use of a torsion bar suspension and lubricated tracks without rubber pads. Ultimately, at the insistence of Krupp engineers and with the aim of saving weight and easing production, the use of the Panzer IV’s suspension was chosen. It weighed 430 kg less than a Panzer III’s torsion bar suspension. In addition, it provided more internal room and was generally easier to maintain. It was already in production, so there would be enough spare parts and it would also help save development time. Krupp still proposed that the Army should test a prototype that used a six-wheel bogie suspension. While Wa Prüf 6 considered and even issued a production order for a prototype equipped with this suspension for testing, it was eventually canceled, and no such vehicle was built.
For the construction of this vehicle, the Panzer IV’s original Maybach HL 120 TRM engine, giving out 265 hp@2,600 rpm, was replaced with a much weaker Maybach HL 66 P, providing 180 hp@3,200 rpm. The engine was then connected to a forward mounted SSG 46-type transmission. Initially, a MAN Cletrac-type steering unit was to be used. However, this was replaced with a standard Panzer IV steering unit to simplify production.
With these changes, the maximum speed dropped considerably to 27 km/h. Krupp engineers were alarmed by the reduction of speed and requested that the transmission be changed. A possible replacement was the A.K.6 S 55, but this was not yet properly tested. To avoid delaying the project, it was decided to keep the SSG 46 transmission despite the reduction in speed. The change of engine also reduced the overall operational range, which was 170 km on road and 120 km cross-country. The fuel tanks were located in the front part of the hull, but their capacity is not specified in the sources.
The engine itself was moved to the center of the hull in order to allow for the necessary room for the crew. The engine was placed in a fully enclosed casing. Two ventilation ports were placed above the engine compartment. This arrangement would later be used on many German vehicles adapted for various roles, including the 15 cm armed Hummel self-propelled artillery, which was also based on the Panzer IV.
The decision to replace the engine with a weaker one was mainly motivated by the need to keep the vehicle’s overall height as low as possible. This decision would greatly and negatively affect the overall drive performance of the 10.5 cm K (gp.Sfl.). Given the reduction of speed, the whole point of providing a mobile support vehicle was lost. In order to engage a target, the whole vehicle had to change positions often, and, together with a weaker engine, often led to overheating problems.
For the construction of the superstructure of this vehicle, the Germans especially wanted to avoid using complex-shaped armor plates. Instead, they went for the simplest design possible. Starting from the front, the Germans added an enclosed housing to the left of the gun, where the driver was positioned. It was a simple box-shaped compartment with a front mounted pivoting driver vision port, vision slit to the left, and a hatch on top. The driver’s protective visor, the Fahrersehklappe 50, was 50 mm thick. When the visor was closed, the driver would use a binocular periscope to see through two small round ports located just above the visor. Opposite this compartment, the Germans placed another fake one. It was meant to confuse enemy gunners, so that they had a harder time hitting the driver.
The front superstructure plate armor was made of one large piece with a hole in the center for the gun itself. The side armor consisted of four welded armor plates. The lower two were placed straight up, while the upper two were slightly angled toward the center of the vehicle. The upper part of the side armor was cut down as it went toward the rear part of the vehicle. This was done intentionally to reduce the weight of the vehicle and would appear commonly on many later German vehicles of similar design. The rear part of the vehicle was protected by one larger armor plate. Two escape hatches were placed there.
The top part of the vehicle was mostly open. The exception was the front part of the vehicle, where the gunner’s periscope was positioned. In front of it was a small bullet splash protector. The rear part of the vehicle was also lightly protected in order to provide the loaders with some level of protection against aerial attacks. The crew fighting compartment was left open to facilitate ventilation of the smoke created during gun firing. It also provided a good view of the surroundings, reduced production cost, and overall weight. The downside though is obvious, as the crew was exposed to enemy fire and the elements.
The thickness of the armor, like many other components, was determined by the weight limitations of the vehicle. To prevent the vehicle from becoming too heavy, the armor was kept relatively light. To enhance protection, the front armor plates were face-hardened.
The front hull had a thickness of 50 mm, while the upper front superstructure armor measured 30 mm. The box-shaped gun mantlet had a thickness of 50 mm. In contrast, the side hull and superstructure armor were thinner, measuring only 20 mm. The rear armor was even lighter at 10 mm. The upper armor varied between 10 and 20 mm in thickness.
The Germans made an intriguing addition to the vehicle by including a thin armor cover for the ammunition bins, even though the crew compartment was open-top. This feature aimed to offer some protection against potential attacks from enemy aircraft. However, doubts remain regarding the actual effectiveness and practicality of this measure.
In general, the armor thickness of the vehicle was considered relatively insufficient when compared to the standards of 1941. Nonetheless, the presence of a powerful and long-range gun helped alleviate this concern to some extent. The vehicle had the ability to engage targets from a distance, potentially preventing them from mounting effective counterattacks, at least in theory.
Main Armament – The 10.5 cm K18 Gun
The main armament chosen for this vehicle was the 10.5 cm K18 gun, which had been developed in the late 1920s. The designation “K18” was intentionally misleading, as the Germans were prohibited from developing new artillery after World War I. By using designations that falsely implied it was a pre-World War I design, they were able to bypass these restrictions. The K18 gun incorporated elements from both Krupp (carriage) and Rheinmetall (gun), which were merged together into a single design. Production began in 1933 after a successful testing phase, following a standard pattern similar to other modern German artillery pieces.
The gun featured a split-trail carriage and was connected to two large leaf-spring-suspended solid rubber-rimmed wheels. The barrel, housed in a protective jacket, was a single-piece design connected to a horizontally sliding breech. The gun was designed for towing by trucks or half-tracks, and if necessary, it could also be towed by horses, although in this case, the barrel had to be removed and placed on another trailer. It had a traverse range of 64° and an elevation range of 0° to +48°. With the strongest charge, it had a maximum firing range of just over 19 km. The gun weighed 5,640 kg when in action.
Despite its relatively long-range capabilities, the 10.5 cm K18 gun was considered to have a small caliber, despite its large size. However, it remained in use until the end of the war. An interesting aspect is that in the early stages of the war and during the invasion of the Soviet Union, it was often employed in anti-tank roles.
In order to fit inside this particular vehicle, the 10.5 cm gun had to undergo redesign. The gun was removed from its carriage and placed on specially designed mounting points located on top of the engine compartment. To accommodate the limited space, smaller recoil cylinders and recuperators were utilized. These modifications allowed for the omission of a large gun mantlet. Despite the reduced size, the gun maintained a sustained rate of fire of 120 rounds per hour (2 rounds per minute). A large muzzle brake was incorporated into the design, although it was later replaced by a smaller one when the gun was deployed on the frontlines. Additionally, a large travel lock was added to the front of the gun to support its heavy weight and long barrel.
The design of the vehicle’s gun system had some shortcomings, particularly in terms of its limited traverse and elevation capabilities. The gun had a traverse of only 16° and an elevation range of -15° to +10°. To operate the gun, the control wheels for both elevation and traverse were positioned on the left side of the vehicle, ensuring convenient access for the gunner. Each full rotation of the traverse wheel resulted in a traverse speed of 0.7°, while the elevation speed ranged between 0.7° to 0.8° per wheel turn.
The 10.5 cm gun exhibited remarkable anti-tank capabilities that served as a notable strength despite its design limitations. With a muzzle velocity of around 822 m/s (this varies slightly in different sources), it could penetrate up to 155 mm of armor at a range of 500 m. At a distance of 1 km, it was capable of defeating 128 mm of armor, and at 1.5 km, it could pierce 111 mm of armor. These exceptional performance characteristics established it as one of the most effective anti-tank weapons during the early years of the war.
The 10.5 cm gun employed a two-part ammunition system, comprising a propellant and a round. Although this type of ammunition slightly reduced the firing rate, it offered several advantages. It facilitated convenient storage within the vehicle and allowed for loading regardless of the gun’s position. Additionally, during firing, the gunner had the flexibility to utilize one or more charges as required. The ammunition load for the vehicle consisted of a total of 26 rounds, which were stored both on the right side of the crew compartment and in close proximity to the driver’s position.
The gunner would employ the Selbstfahrlafetten-Zielfernrohr for direct firing, specifically targeting enemy armor. However, when fulfilling the role of mobile artillery for firing support at long distances, the Rundblickfernrohr 34 would be utilized instead. The effective range for direct firing was limited to 3 km, providing the 10.5 cm gun with substantial firepower to engage distant targets. Nevertheless, due to various factors such as poor visibility, adverse weather conditions, ammunition quality, or sheer luck, engaging enemy armor at longer ranges was infrequent.
While no secondary machine gun was incorporated, the crew members were equipped with 4 MP 40 submachine guns for close self-defense purposes alongside two magazine pouches for each weapon.
The crew of the vehicle consisted of five: commander, driver, gunner, and two loaders. The driver enjoyed full protection as he was situated in the small driver compartment. The commander occupied the position on the right side of the gun and was equipped with a doppelscheren Turmspaehfernrohr scissor periscope for observing the surroundings. The periscope offered a 3x magnification and a 20° field of vision. Positioned opposite the commander was the gunner, while the two loaders stood behind them, prepared to load the gun.
Organization and Doctrine
The two 10.5 cm K (gp.Sfl.) were assigned to one of the most famous German early to mid-war anti-tank units, Panzerjäger Abteilung 521 (Anti-Tank Battalion 521). This battalion fielded various anti-tank weapons, including the Panzerjäger I and the larger Panzerselbstfahrlafette für 12,8 cm Kanone 40. During Operation Barbarossa, the unit was initially part of the XXIV. Army Corps and later came under the command of the 3rd Panzer Division in September 1941. It was later incorporated into the XVII. Army Corps and participated in the Battle of Stalingrad, where it was ultimately destroyed as part of the 6th Army.
Within the Anti Tank Battalion, the two 10.5 cm K (gp.Sfl.) were organized into a new platoon, which consisted of a fighting column and an ammunition transport column. The fighting column included two 10.5 cm K (gp.Sfl.) vehicles, two Kfz.4 anti-air defense cars, and a Kfz.15 radio communication vehicle. This composition allowed for both direct and indirect fire capabilities, contributing to the battalion’s effectiveness in combat.
The primary purpose of this particular self-propelled gun was to engage and destroy heavily fortified concrete bunkers at long distances, all while maintaining its mobility on the battlefield. Additionally, it served as a formidable weapon against heavy tanks that were impervious to other anti-tank weapons. However, due to its delayed deployment, it did not have the opportunity to fulfill its original intended role during the events in France in 1940. Instead, when it was eventually sent into the Soviet Union in 1941, its focus shifted primarily to its secondary role of engaging and combating enemy tanks.
First stage – Operation Barbarossa and Early Losses
The following reports come from Panzerjäger Abteilung 521, which participated in the invasion of the Soviet Union on 22nd June 1941. The first operational report comes from 24th June 1941.
The platoon was employed in a vanguard in the fight around the area east of Kobryn, where it fired HE rounds at infantry positions. In the evening, the platoon was supporting an attack by motorcycle gunners that crossed over a river. The SPGs engaged open artillery at a range of 1,100 to 1,700 m and successfully disabled them.
During the advance on Slutsk on June 26th, 1941, an unfortunate incident occurred which resulted in the destruction of one of the self-propelled guns. Although the exact cause was not definitively determined, it is believed that the intense heat generated from the engine, combined with the exceptionally high temperatures outside on that day, led to a buildup of heat. Within the area, a small quantity of high-explosive (HE) grenades was stored, which likely ignited as a result.
Fortunately, the crew members were quick to react when they noticed a small burst of flame, allowing them to promptly evacuate the vehicle. All five crew members observed the SPG continuing to move for a short distance before coming to a halt. However, shortly thereafter, the flames spread and reached the main ammunition storage, causing a catastrophic fire. As a result, the vehicle was completely destroyed and had to be abandoned at the roadside. Remarkably, despite the loss of the vehicle, it was reported that the gun of the SPG remained intact and was still usable.
On June 30th, 1941, the final remaining self-propelled gun confronted a Soviet armored train but was unable to halt its escape to safety. The SPG encountered an internal problem with one of its components, specifically a broken bolt in the slide mechanism of the steering brakes. This malfunction significantly impeded the gun’s ability to aim accurately at the target. Consequently, the team lost approximately 5 minutes of crucial time, during which the armored train managed to elude capture and find a secure location.
On August 20th, 1941, the self-propelled gun found itself engaging an enemy column from a considerable distance of over 4,000 m. This was primarily due to the absence of a closer firing position that would ensure the SPG’s safety. As the enemy tanks opened fire, their long-range shots and the continuous movement of the column hindered their ability to aim accurately, providing relative safety for the SPG.
To engage the column, the SPG employed high-explosive (HE) grenades with delayed fuzes set to the maximum range of 2,400 m. Although the crew initially estimated the distance to be 3,000 m instead of the actual 4,000 m, they skillfully targeted the column with well-placed hits and multiple spotting shots. Following the German tank crew’s training protocol for column destruction, the gunner aimed at the first tank in the column using a pre-loaded HE grenade. While a direct hit was not achieved, subsequent observation revealed damage to the tank’s tracks.
Continuing the engagement, the SPG fired three additional rounds of regular armor-piercing ammunition at the same tank. However, none of the shots hit their mark, as the gunner had to rely on trial and error to adjust the gun’s elevation beyond the effective range of 2,400 m. Later, it was observed that the crew of the enemy tank, identified as a KV-1, intentionally destroyed their own tank and managed to escape.
In addition to the destruction of the first tank in the column, two more tanks, likely T-34/76 mod.1941s, met a similar fate. The rounds fired by the SPG caused damage to the suspension of these tanks, rendering them immobile. Subsequently, the crew of each tank took the decision to set their vehicles on fire, effectively destroying them.
During a defensive battle on August 29th and 30th, 1941, the Battalion encountered Soviet tanks. On the 29th, the gunner and commander of the SPG scouted the area to identify suitable defensive positions and gain a better sense of the distances to specific points, making the aiming process easier. Upon returning to the tank, a Soviet T-34 approached their position, unaware of the presence of the SPG. Exploiting this advantage, the crew successfully destroyed the tank at a close range of 100 m. Subsequently, they engaged a second T-34 at approximately 1,000 m, managing to immobilize it. However, the Soviets recovered the disabled tank under the cover of darkness later that night.
On August 30th, 1941, the SPG encountered a T-34 tank and two T-26 light tanks positioned approximately 1,200 m away. However, the SPG was unable to advance closer due to the presence of Soviet anti-tank positions in the area. Despite the challenging circumstances, the SPG successfully immobilized the T-34 tank but failed to hit the T-26 tanks, which managed to escape into a nearby forest.
Regrettably, the available records for the 10.5 cm, K (gp.Slf.) conclude at this point. Towards the end of 1941, the sole surviving vehicle was withdrawn from the frontlines.
Second stage – Into Stalingrad
After being withdrawn from the frontlines, the SPG underwent extensive repairs and maintenance at the Krupp facilities. The vehicle required significant repairs and was repainted, resulting in the loss of its kill markings. During this time, Krupp proposed using a new Panzer IV chassis, but the Army Design Office rejected the offer, stating that the existing suspension would suffice.
In spring 1942, the SPG was deployed back to the frontlines, once again assigned to Panzerjäger Abteilung (Sfl.) 521, which had survived the unsuccessful attack on Moscow in the winter of 1941. Alongside two similar vehicles, known as the Panzerselbstfahrlafette für 12,8 cm Kanone 40, the SPG was expected to be combat-ready by June 1st, 1942. It subsequently participated in operations such as Case Blue and the assault on Stalingrad, with the objective of capturing the oil fields near Stalingrad.
During this period, from spring to October 1942, the recorded history of the SPG is scarce, suggesting that the Army Design Office had less interest in its performance. It is likely that the vehicle was seen more as a reserve vehicle to plug equipment gaps in the Wehrmacht, rather than a subject for further testing or development. By this time, the Army Design Office had likely accumulated sufficient knowledge and experiences from previous operations, diminishing the need for detailed documentation of the SPG’s activities during this period.
The SPG met its demise in October 1942, as indicated by the absence of any mention of the vehicle in inventory reports from November and December of that year. The last known photograph of the tank was taken in December 1942 by Soviet soldiers. In the photo, the vehicle is seen in its original dark gray color with patches of sand yellow applied over it. Additionally, the tank underwent white washing, resulting in an interesting camouflage pattern. This type of camouflage was commonly employed by vehicles entering combat during the summer of 1942. The SPG featured a total of 18 kill rings and a small tank symbol painted on the barrel, reminiscent of the markings added by the crew in 1941.
According to the Army Design Office’s request, the crews and unit were tasked with closely monitoring and describing the flaws and performance of the 10.5 cm, K (gp.Slf.) during combat. The following points are based on reports from July to September 1941, shortly before the second vehicle was sent back to Germany:
- The vehicle’s effectiveness in the vanguard was limited due to its lack of maneuverability. With a combined traverse of only 18°, the entire tank needed to turn even for minor adjustments. This, combined with the vehicle’s weak engine and heavy weight, significantly slowed down the aiming process. Furthermore, since only the frontal armor provided adequate protection, the tank crew had to constantly be vigilant to avoid being flanked and always keep its front facing the enemy. The nature of vanguard operations demanded the ability to engage targets from any direction without encountering such challenges.
- The tank had proven its effectiveness in providing support to infantry attacks from open positions through direct fire. However, a significant challenge arose from the large dust cloud generated in front of the gun, which hindered the observation of the tank’s own shots. To overcome this issue, it was deemed crucial to deploy an observation post or a dedicated team led by a fire control non-commissioned officer (NCO) who possessed knowledge of both the crew and the vehicle. This team’s role was to provide accurate observations and assist in adjusting fire, thereby maximizing the tank’s effectiveness in combat situations.
- The tank had not yet been utilized in its intended role as a concrete bunker destroyer with direct fire. However, its large caliber and high penetration demonstrated in the destruction of medium tanks indicated its effectiveness.
- The transmission and engine did not encounter any major issues. However, there were concerns regarding the overstressing of the steering brakes, leading to bolts in the steering slide tearing out.
- Achieving direct hits on heavy tanks like the KV-1 at ranges of 4,000 m proved challenging. Destruction or damage to the suspension primarily resulted from shell fragments, which sometimes led the crew to abandon and destroy their tank. However, this occurrence was not consistent, with instances where the enemy crew managed to tow their tank away during nighttime.
- Due to the gun’s capability in engaging soft skin targets up to 4,000 m, it was recommended to mark the range scale accordingly. However, most armored targets could only be effectively engaged at a range of 1,500 m.
- Prior to each firefight, it was crucial to scout the terrain in order to identify an optimal firing position. This task could be carried out by either the commander or the gunner.
- Engaging moving targets proved challenging, especially at longer distances. The limited traverse of 9º on either side was insufficient for pre-aiming at targets over large distances.
- It was not recommended to engage heavy tanks directly at ranges exceeding 1,000 m, as achieving penetration became increasingly challenging. Additionally, there was limited visibility monitoring the impact location of projectiles. Therefore, it was advised to engage tanks only within a range of up to 1,000 m.
- In order to facilitate indirect fire with high-explosive grenades, the inclusion of a rangefinder was seen as crucial, especially for ranges exceeding 1,000 m.
- The commander’s observation periscope proved insufficient and had to be replaced with a standard Scherenfernrohr (scissor telescope) for improved observation capabilities.
The encountered challenges and experiences played a vital role in the development of subsequent German self-propelled guns (SPGs), such as the Wespe and Hummel. These vehicles incorporated several of the necessary upgrades derived from the lessons learnt.
The 10.5 cm, K (gp.Slf.) served as a well-conceived initial endeavor to create a specialized self-propelled gun (SPG) dedicated to the destruction of heavy bunker positions. However, like many first attempts, it exhibited several design flaws and performance concerns on the battlefield. Nonetheless, the project held significant importance for both Krupp and the Army Design Office, as it provided valuable insights and lessons in terms of combat performance. These experiences proved instrumental in the development of subsequent SPGs during the war. Moreover, the knowledge gained alone rendered the vehicle useful for the German Army, despite its imperfections.
Furthermore, the vehicle’s actual combat performance demonstrated its effectiveness as a tank destroyer, as the second vehicle showcased its capability by successfully destroying numerous Soviet medium tanks with its powerful gun. However, it is important not to overlook the negative aspects, which significantly impacted the vehicle’s mobility and overall performance. The design flaws, in particular, played a pivotal role in the destruction of the first vehicle, highlighting a potential recurring problem if larger numbers had been produced, akin to the issues faced by many Ferdinand tank destroyers in 1943.
10.5 cm, K (gp.Slf.) Specifications
|Dimensions (L-W-H)||7.47 x 2.86 x 2.53 m|
|Total Weight||22 tonnes|
|Crew||5 (driver, 2 loaders, gunner, commander)|
|Speed||On roads 27 km/h, off-road 17 km/h|
|Range||On roads: 170 km, off-road: 120 km|
|Armament||10.5 cm Kanone L/52
3x 9 mm MP 40
|Engine||Maybach HL 66 P, 6 cylinder water cooled, 6.6-liter gasoline, 180 hp|
|Ammunition||26 10.5 cm (HE and AP) shells
576 9 mm rounds
|Elevation||-15° to +10°|
|Gunsight||Sfl.Z.F.1, 2x 20 degrees, 3400 m for AP, 2400 m for HE|
|Power Ratio||8.2 hp/tonne|
|Ground clearence||40 cm|
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