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WW2 German SPGs

Gepanzerter 8t Zugkraftwagen and 8.8 cm BuFlak ‘Bunkerknacker’

Germany (1938-1940)
Armored Towing Vehicle – 25+ Built
Anti-Aircraft Gun – 33 to 50 Modified

Prior to the Second World War, the Germans were aware that they would need weapons that could deal with enemy fortified positions, such as bunkers. Their anti-tank guns and most of the artillery were not suited for this task. During the Spanish Civil War, the 8.8 cm Flak anti-aircraft gun proved to be quite effective when used against ground targets. Thanks to its large caliber and high velocity, the German Army officials came up with the idea of modifying some of them for use against enemy bunkers. Around 50 or so guns would be modified and used during the invasion of the West in 1940.

Heavily modified Sd.Kfz.7 half-track with the specialized 8.8 cm Flak gun.Source: https://www.worldwarphotos.info/gallery/germany/halftracks/sdkfz-7/

A Brief  8.8 cm Flak History 

In search of a new anti-aircraft gun, Krupp was contacted by German Army officials to develop such a design. In 1931, Krupp engineers returned to Germany after spending years cooperating with the Swedish Bofors company to begin construction of the gun under the most secret conditions. By the end of September 1932, Krupp delivered two guns and 10 trailers. After a series of firing and driving trials, the guns proved to be more than satisfying, and, with some minor modifications, were adopted for service in 1933 under the name 8.8 cm Flugabwehrkanone 18 (Eng: anti-aircraft gun) or, more simply, Flak 18.

Its overall anti-aircraft performance was similar to other nations’ heavy anti-aircraft guns. It gained its fame as an excellent anti-tank weapon in the early years of the war. This gun helped the Germans when other weapons failed them in this role. It would remain in German use up to the war’s end, with over 20,000 such guns being built. Many, including copies, would see service for several more decades.

The 8.8 cm Flak 18. Source: Pinterest

Not a Ground Attack Weapon 

Despite its fame as an excellent anti-tank weapon during the war, the 8.8 cm Flak was not intended to fulfill this role. Proof for this can be seen in a Wa Prw document dated October 1935. In it, a list of all available anti-tank weapons that were in use or under development was mentioned. In addition, weapons and guns that could be used in this manner were noted too. This included some 2 cm and 3.7 cm caliber anti-aircraft weapons. Somewhat surprisingly, the 8.8 cm Flak gun was not mentioned for potential use as an anti-tank weapon. Two years later, armor-piercing rounds for the 2 cm and 3.7 cm anti-aircraft guns were included in the anti-aircraft development program. The 8.8 cm caliber was once again not included, and thus, no armor-piercing rounds for it were to be developed.

The Germans at this point did not consider the 8.8 cm Flak to be a viable anti-tank weapon. The main reasons for this were its sheer size, the difficulty of movement once employed, and concealment. The only German anti-tank gun that was in service during this time was the 3.7 cm PaK 36. It could be easily moved by only a few crew members, was a small target, and had sufficient firepower to deal with most of the tanks from that era.

When the war in Spain broke out in 1936, the Germans responded to Francisco Franco’s call for aid. The Germans dispatched both ground and air forces to Spain, including a small number of the 8.8 cm Flak guns. As the Nationalists gained the upper hand in the air, the 8.8 cm guns were employed for the destruction of ground targets, where their firepower showed that it had great potential in this role. Thanks to their half-track towing vehicles, mobility was not a major issue, as these possessed good overall drive on-road and off-road.

Even before the Spanish War ended, in 1938, the Heereswaffenamt (German Army weapons agency) and, more importantly, Adolf Hitler himself, requested that the 8.8 cm Flak 18 be adapted for use against ground targets. Their primary missions would be to destroy enemy fortified positions, such as bunkers, but also tanks if any came into range. Mobility was a major factor, as the gun had to be quickly positioned to take action against enemy targets. Two proposals would be adopted. The first would be 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.

Some 10 8.8 cm Flak 18 Sfl. auf schwere Zugkraftwagen 12 t (Sd.Kfz.8) als Fahrgestell would be built. While having a number of issues with their overall design, these vehicles would prove to be effective anti-tank weapons during the war. Source: en.wheelsage.org

The latter version was known as the 8.8 BuFlak (Bunker Flak). Given its purpose, the destruction of enemy bunkers, these 8.8 cm guns are sometimes referred to as Bunkerknacker (Eng: bunker destroyer). It is important to note that this name was not only used to describe the 8.8 cm gun, but also for other weapons that performed similar roles, such as the 10.5 cm K 18 guns. The term  Gepanzerte Flak is also sometimes used. The towing vehicle was designated as Gepanzerter 8t Zugkraftwagen.

Increasing the 8.8 cm Flak gun’s mobility was to be achieved by firing the gun while still connected to its two-wheeled bogies. In this way, the crew would not need to waste time lowering the gun and removing the bogies. A new shield was to be added to the gun for crew protection, albeit minimal in scope. In addition to protecting the crew, their towing vehicle would be armored as well. The vehicle chosen for this conversion was the Sd.Kfz.7, which was the standard towing half-track for the 8.8 cm Flak gun prior to and during the war.

The first wooden mock-up of the modified Flak gun. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak

Production

In order to implement what was seen as an urgent project, Rheinmetall was contacted in August 1938. Rheinmetall engines worked hard, completing the wooden mock-up by 19th August. Only a week later, the first prototype was completed and tested at Kummersdorf. By the end of September, around 50 such modified guns would be built. Authors, such as  T. Anderson (History of Panzerwaffe Volume 1 1939-42), mention that 33 guns were modified this way.

While the number of the modified guns is known, the precise number of modified towing vehicles is unknown. Authors T.L. Jentz and H.L. Doyle (Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak) mention that, thanks to photographic evidence, it is known that at least 25 such vehicles were built, though possibly more. The first vehicles were completed in mid-1938.

Design of the 8.8 cm BuFlak Gun

The Gun 

The 8.8 cm Flak 18 used a single tube barrel which was covered in a metal jacket. The barrel itself was some 4.664 meters (L/56) long. The gun recuperator was placed above the barrel, while the recoil cylinders were placed under the barrel.

The 8.8 cm gun had a horizontal sliding breechblock which was semi-automatic. It meant that, after each shot, the breach opened on its own, enabling the crew to immediately load another round. This was achieved by adding a spring coil which was tensioned after firing. This provided a good rate of fire of 15 rounds per minute when engaging ground targets. Despite its maximum range of 15.2 km (with a muzzle velocity of 840 m/s), modified Flak guns were meant to engage enemy bunkers and positions in ranges of less than 1 km.

The modified Flak guns received a slightly changed Flakzielfernroht 20E telescopic sight. Its original use of degree grading was replaced with meters. The gunsight was positioned some 71 cm to the right and 20 cm below the gun. The gunner had to take this into account during firing. The gunsight had to be accordingly positioned slightly to the right and below the target.

The crew manual for this weapon notes that the best and most stable firing position was when the gun was facing forward or to the rear. When fired to the sides, great care had to be taken so that the gun could take the firing recoil. No source provides a precise weight of this gun, but given that it received minimal modifications, it would likely remain the same or quite similar to the original, which had a weight in firing position of 5,150 kg, while the total weight was 7,450 kg.

Controls

Initially, the Flak 18 had two handwheels, one responsible for elevation or one for the traverse. These were located on the right side of the gun. In essence, this meant that two crew members were needed to fully control the movement when tracking targets. The Flak gun that was intended to be solely used for ground operations had to have changed controls. The two separate handwheels were replaced with a single operating unit that contained both of these controls. This new control unit was placed on the forward right side, close to the shield. Essentially, this meant that only one crew member, the gunner, was needed to fully engage targets. Due to its primary mission of engaging ground targets, the elevation was limited to -4° to +15°.

Carriage

Given its size, the gun used a large cross-shaped platform. It consisted of the central part, where the base for the mount was located, along with four outriggers. The front and the rear outriggers were fixed to the central base. The gun barrel travel lock was placed on the front outrigger. The side outriggers were shorter in contrast to those originally used. On these two side outriggers, the round-shaped leveling jacks were replaced with a new square-shaped jack. Their purpose was to prevent the gun from digging into the ground and to keep the gun level on uneven ground.

The modified 8.8 guns had side outriggers that were shorter in comparison to those of normal guns. Also note the new square-shaped jacks. Source: www.worldwarphotos.info  
In comparison, the original side outriggers were longer and had round-shaped leveling jacks. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. Dreaded Threat The 8.8 cm FlaK 18/36/47 in the Anti-Tank role

Bogies

The whole gun was moved using two-wheeled bogies designated as Sonderanhanger 201. The front bogie had single wheels, while the rear one consisted of a pair of wheels per side. Another difference between these two included that the front bogie had 7 and the rear 11 transverse leaf springs. The wheel diameter was the same for the two, at 910 mm. These were also provided with air brakes. In contrast to ordinary guns, this version was to be fired while the two bogies were still connected to the gun carriage.

These guns were to be fired by still connected to the two bogies. This made them rather tall targets for enemy gunners. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak

Shield 

Another new implementation was the introduction of a slightly modified armored shield. It had a simple rectangular shape and was placed at an angle. To the right, there was a hatch that could be closed if needed. Its purpose was to provide the gunner an opening to spot his targets. While an ordinary 8.8 cm Flak front armor shield had a small opening on top for the gun to elevate to the sky, this gun shield did not have it, and it was instead covered with a plate. To somewhat further increase the gun operator’s protection, two smaller triangle-shaped side armor plates could be expanded to both sides. When on the move, these were folded to the front armor shield. The precise armor thickness is not listed in the sources, but it is mentioned that it was slightly thicker than the 10 mm used on the original 8.8 cm Flak shield. While not particularly thick, it was intended to protect the crew from small-caliber rounds and shrapnel.

Front view of the new gun shield, which was slightly enlarged. As the upper part of the shield was enclosed, the gun could not be used to target enemy aircraft. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak  
For comparison, the armored shield used on ordinary 8.8 cm guns had an opening at the top which enabled the crew to elevate the gun barrel to engage air targets. In addition, it was somewhat smaller in dimensions. Source: www.deviantart.com

Ammunition

The modified Flak gun was mostly meant to fire high-explosive and anti-tank rounds. The 8.8 cm Sprgr Patr was a 9.4 kg high-explosive round with a 30-second timed fuze. The 8.8 cm Pzgr Patr was a 9.5 kg standard anti-tank round. With a velocity of 810 m/s, it could penetrate 95 mm of 30° angled armor at 1 km. At 2 km, at the same angle, it could pierce 72 mm of armor. Using an armor-piercing round, at 70° angle, it could penetrate 1 m of concrete at 1 km distance. As these guns could not be used in their original role, the fuse setting device was replaced with a box-shaped ammunition bin that contained 6 rounds of ammunition.

Another modification was the introduction of ammunition storage for six rounds, which was placed where the fuse setting device was originally located. The ammunition box on this gun is currently empty. Due to its high rate of fire, the ammunition could be easily spent in a short amount of time. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak

Crew

The vehicle with the gun had a crew of 7. This consisted of the commander, loader, gunner, and four additional gun assistants. The gunner was placed on the right side of the gun and was responsible for operating the gun traverse, elevation, and firing mechanism. Left of the gunner was the loader’s position. Due to the use of bogies during firing, the height of the gun was raised. In order for the loader to be able to load a new round, a metal platform was welded on this side to stand on. The commander and the remaining crew were responsible for moving the gun, carrying additional ammunition, and spotting targets.

Due to its increased height, it was necessary to add a platform for the loader. Also, note the smaller shape of the lowered side outrigger. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. Dreaded Threat The 8.8 cm FlaK 18/36/47 in the Anti-Tank role  
Another view of the loader’s positions. The loader was put in a quite precarious and somewhat exposed position, where a well-placed enemy bullet could easily end his life while loading the gun. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak

The Gepanzerter 8t Zugkraftwagen 

The primary towing vehicle for the 8.8 cm Flak guns was the Sd.Kfz.7 half-track, although it was also not uncommon to see heavy 6×6 wheeled trucks being used in this role. The Sd.Kfz.7 was developed in the mid-1930 by Krauss-Maffei. During its production run, some changes to its design would be implemented, mostly in an attempt to increase its overall performance. This would lead to the installation of a stronger engine and adding two more road wheels per side. The performance was deemed satisfactory and some 12,000 such vehicles would be built up to 1945. The Sd.Kfz.7 also saw limited export success, being sold in small numbers to Brazil, Hungary, Japan, the Soviet Union even Great Britain after the war. It was also built in Italy under the Breda 61 designation.

As the previously mentioned 8.8 cm guns were to be used for destroying enemy fortified positions at relatively close ranges, a soft-skin towing vehicle was deemed undesirable for this task. For this reason, unknown numbers of Sd.Kfz 7 was modified, receiving an armored body to protect the engine, crew, and ammunition.

The Sd. Kfz. 7 half-track in its original configuration. Source: wwiitank.wordpress.com

Chassis and Suspension

The Sd.Kfz 7 chassis and its suspension seem to have been unchanged. The suspension consisted of 6 road wheels, a rear idler, and a front positioned drive sprocket. The front four wheels were suspended using a balance suspension. The remaining wheels were placed on a pivoting arm suspended using a semi-elliptic leaf spring unit.

The armored Sd.Kz. 7’s suspension and overall chassis construction seem to have been unchanged. Also, note the side hatch door located beneath the driver compartment. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak

Crew

The crew of this vehicle consisted of only the driver, who was positioned on the front left side of the driver compartment. During the drive, the commander would sit next to the driver. The remaining crew were located in the rear crew compartment.

Armored Body

The armored body of this vehicle resembles that used on the Sd.Kfz.251 armored half-track. It was well angled and covered the whole length of the rear compartment. In addition, it was open-topped. The armor thickness of the plates used for this vehicle was 15 mm. With this thickness and with the angled sides, it provided sufficient protection from small-caliber rounds and artillery shrapnel only.

The armored body of this vehicle could basically be divided into a few sections: the engine compartment, the driver compartment, the crew compartment, and the ammunition storage bin. The engine’s sides and front were fully enclosed with an armored shield. On both sides, there were four large hatches. These could be opened to provide better ventilation for the engine. The top of the engine compartment was not protected.

The engine front and side were fully protected. On each side, there were two hatch doors that could be opened for better engine ventilation. Source: www.armedconflicts.com

The drive compartment was slightly raised up from the rest of the armored body. It was open-topped and had four protective hatches, two at the front and one on each side. In addition, on the bottom of the sides of the driver compartment, two larger hatches were located. Their purpose is not clear, and they served either for some kind of storage or to allow the driver and the commander to exit the vehicle. Behind was the gun crew compartment. The crew was positioned on two benches placed opposite each other. In order to exit the vehicle, there was a hatch at the rear of this compartment. Lastly, to the rear of the vehicle, box-shaped armored ammunition storage was located. It contained some 24 spare rounds of ammunition.

The top of the engine compartment was left unprotected. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak  
Top view of the driver’s position. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak  
The ammunition storage could hold 24 rounds to the rear of the vehicle. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak

Performance

The ordinary Sd.Kfz.7 vehicles had a 140 hp HL 62 TUK engine and could reach up to 50 km/h. With a fuel load of 213 liters, the operational range on roads was 250 km, and 135 km off-road. The length of this vehicle was 6.85 meters, width 2.4 meters, and height 2.62 meters. While the performance of the Gepanzerter 8t Zugkraftwagen is not mentioned in the sources, the additional weight from the armor plates probably affected its overall performance. To which extent this was the case it is quite difficult to know.

Either due to losses or some other reasons, ordinary unarmored Sd.Kfz 7 half-tracks would sometimes be used as towing vehicles, like in this case. Source: T. Anderson History of Panzerjager Volume 1 1939-42

Training and Organization  

By the order of the Oberkommando des Heeres (Eng. German High Command), the training of the first crews that were to operate these guns was to commence during September 1938. The main training center was to be at the Juterbog artillery school.

Nominally, these were intended to be attached to heavy motorized artillery or anti-tank battalions. The order for the employment of these vehicles was to be issued by the command of an infantry regiment.

Prior to the engagement, the commander, along with two assistants, would go ahead to observe its target, find the best firing position, and the best way to retreat if needed. Once the location was found, the gun was moved to that position. Despite the 8.8 cm gun’s good firing range, targets were to be engaged at less than 1 km. In addition, due to its somewhat limited elevation, great care had to be taken by the crews to choose good firing positions. Given that the crew had to come rather close to the target, hiding and camouflaging the gun was seen as essential. Because of its sheer size, in practice, this would be a difficult task to undertake in close proximity to the target. Smoke screens were meant to be used while the gun was preparing to fire.

These units were to be primarily used in destroying enemy fortified positions, such as bunkers. Since the target hit rate was expected to be around 30%, shooting at greater ranges than that had to be avoided. If enemy tanks came into range, these were also to be targeted.

Some 11 vehicles were attached to the 525th, 560th, and 605th schwere Panzer Jäger Abteilung (Eng. heavy anti-tank battalions) each. Each of these battalions were divided into three companien (Eng. Company).

In Combat

Occupation of The Sudetenland 

The first ‘combat’ use of the Gepanzerter 8t Zugkraftwagen and Sfl.Flak was during the occupation of the Sudetenland in 1938. This operation was peaceful and the 8.8 cm guns did not have to fire in anger. While its self-propelled cousin saw service in Poland, use of the Gepanzerter 8t Zugkraftwagen and the 8.8 cm BuFlak in this campaign is not recorded, which likely suggests that it was never employed there.

The Gepanzerter 8t Zugkraftwagen and Sfl.Flak in the occupied Sudetenland. Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. 22-5 Gepanzerter 8t Zugkraftwagen and Sfl.Flak

In France

The 525th, 560th, and 605th heavy anti-tank battalions would see service during the German West campaign of 1940. During this campaign, they were attached to various units depending on the combat needs. Unfortunately, their overall performance and usage is rather poorly documented.

The 525th heavy anti-tank battalion saw its first action while helping clean Allied road barricades at Trois Ponts on 10th May 1940. The following day, it provided its firepower to the 49th Infantry Regiment that was attacking a bunker. After firing several rounds, the bunker crew surrendered. On 19th May, while driving toward Dinant, two vehicles from the 525th heavy anti-tank battalion ran into an enemy ambush and were hit by machine gun and anti-tank fire. One armored Sd.Kfz 7 was hit by an anti-tank round and was set on fire. The fire would expand to its ammunition storage, igniting it into an explosion. The second vehicle was hit with machine gunfire. Its crew abandoned the gun and used the armored towing vehicle to retreat. An hour later, they returned to recover the damaged gun.  The gun would be repaired that evening and the unit advanced toward Clairefontaine.

The following day, another vehicle arrived to support the attack of the 49th Infantry Regiment at the Allied held Assevent. Elements of the 525th heavy anti-tank battalion participated in this engagement with two guns. One gun was positioned to protect the infantry against enemy armor, which had been spotted. The second gun proceeded forward, but its towing vehicle hit a metal bar which immobilized it. The crew had to sit by this vehicle and wait for a replacement. Soon, the replacement vehicle arrived and the crew continued the advance. Once in a designated position, at least three enemy machine gun positions were destroyed. The crew of this gun noticed that friendly infantry was retreating under fire from enemy B1 bis tanks. One was engaged at a distance of 300 m and destroyed. The second vehicle was hiding behind a wooden hut. As it emerged to target the 8.8 cm gun, it was hit, exploding in the process. Seeing the two tanks destroyed, the German infantry made a counter-attack. These guns were also used to support the 51st Infantry Regiment advancing toward Dunkerque during May 1940.

The Gepanzerter 8t Zugkraftwagen towed an 8.8 cm gun at the start of the German attack in May 1940. Source: /www.armedconflicts.com  
An 8.8 cm firing at Allied positions near Dunkerque in May 1940. Source: W. Muller The 8.8 cm FLAK In The First and Second World Wars  
Despite their armor, the Gepanzerter 8t Zugkraftwagen could still be taken out by almost any anti-tank weapon. Source: www.armedconflicts.com

Following the successful conclusion of the West campaign, the 525th, 560th, and 605th heavy anti-tank battalions were equipped with ordinary towed 3.7 cm anti-tank guns. The reason for this decision is not known. The order for the reorganization of these units did not include an explanation for this decision. Other units (both Heeres and Luftwaffe), which operated normal 88 mm Flak guns were more than satisfied with their overall performance. This is also supported by the German General Staff, which even argued that the 8.8 should be incorporated into each infantry division. A possible reason for the removal from service of the BuFlak may have been poor training and use. Another issue may have been related to the gun’s limited elevation, which prevented it from being operated in anti-aircraft use.

The fate of the guns and towing vehicles is unknown. It is likely that both types which survived the West campaign were converted back to their original configurations.

Conclusion

The Gepanzerter 8t Zugkraftwagen and its modified Flak gun were an attempt to provide the German ground forces with an effective anti-bunker and anti-tank vehicle. Its overall performance is quite difficult to describe due to the lack of sources and information about its use.

While the 8.8 cm gun was unquestionably an effective weapon when used against fortified targets or tanks, this design was rather questionable. The 8.8 cm Flak in its original configuration was already a tall target. The modified gun was even taller, which made it even easier for the enemy to see. The  Gepanzerter 8t Zugkraftwagen, while protected, in contrast to the ordinary towing variant, was often easily taken out due to the required close proximity to the target.

Due to a lack of information, the precise reason why this vehicle and its gun were removed from service is not known. It is likely that this was done more due to its poor organizational usage than due to any major flaws in its design, as the 8.8 cm Flak and the soft-skin towing vehicles would see major action up to the war’s end.

Gepanzerter 8t Zugkraftwagen. Ilustration made by Godzilla  

8.8 cm BuFlak ‘Bunkerknacker’. Ilustration made by Godzilla

8.8 cm BuFlak Specifications

Dimensions 7.7 x 2.2 x 2.9 m
Weight in firing position:  5.150  tonnes
Crew  7 (Commander, loader, gunner, and four additional gun assistants)
Primary Armament: 8.8 cm L/56 gun
Elevation: -4° to +15°

 

Gepanzerter 8t Zugkraftwagen Specification

Dimensions (l-w-h) 6.84 x 2.4 x 2.62 m
Total weight, battle-ready 23.6 tonnes
Crew 1 (Driver)
Propulsion 140 hp HL 62 TUK
Speed  50 km/h
Range (road/off-road) 250 km, 135 km
Armament None
Armor 15 mm

Sources

 

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