Sd.Kfz.251 Ausf.D mit Zwilling 12 cm Granatwerfer 42

German Reich/Yugoslav Partisans (1945)
Self-Propelled Mortar – 1 Modified

The occupation of Yugoslavia by the Axis forces led to nearly five years of heavy fighting and destruction. All warring parties that participated in the fighting in Yugoslavia were often forced to use older equipment and armaments, as not much else was available. While the Germans employed various armored vehicles, these were mostly older or captured equipment. The Yugoslav Partisans could only employ armor captured from the enemy. In order to gain a slight upper hand over the enemy, or to simply improve their firepower, various field and unique modifications were designed and built by both sides. Generally, in rarer cases, some of these were documented, while, for the majority, almost nothing is known besides a few available photographs that prove their existence. One of these was a Sd.Kfz.251 modification equipped with two 12 cm mortars.

A Brief History of the Occupation of Yugoslavia

After the unsuccessful invasion of Greece by Italian forces, Benito Mussolini was forced to ask for help from his German ally. Adolf Hitler agreed to provide assistance, fearing a possible Allied attack through the Balkans would reach Romania and its vital oil fields. On the path of the German advance towards Greece stood Yugoslavia, whose government initially agreed to join the Axis side. This agreement was short-lived, as the Yugoslavian government was overthrown by an anti-Axis pro-Allied military coup at the end of March 1941. Hitler immediately gave an order for the preparation for the invasion of Yugoslavia. The war that began on 6th April 1941 was a short one and ended with a Yugoslavian defeat and the division of its territory between the Axis powers.
Following the collapse of Yugoslavia, the occupying Axis forces did not expect any major trouble to come from this part of Europe. Unfortunately for them, very quickly, two resistance groups sprang up, the Royalist Chetniks and the Communist Partisans. What followed was five years of heavy struggle, suffering, and destruction on all warring sides in Yugoslavia. While the resistance movements were initially small in scope, by 1944, the Communist Partisans movement combat strength reached several hundreds of thousands. They also employed armored formations consisting of vehicles that were either supplied by the Allies or captured by the enemy. While many Axis allies were present in occupied Yugoslavia, German forces were by far the largest and best equipped. This did not mean that these German units were supplied with the best equipment. Instead, they were mostly equipped with older, captured, or even obsolete weapons and vehicles. But even this, in many cases, was better than the weapons of other participants on this front.

Field Modifications

The combat operations in occupied Yugoslavia would see the use of a number of rare, obsolete, or captured equipment, along with some more modern ones. The most common in use were the French armored vehicles employed by the Germans. After 1943, these were mostly replaced with Italian vehicles, which were also captured by the Germans after their former ally surrendered. Given the Partisan’s lack of any kind of anti-tank weapons, except on the rare occasions when such weapons were captured from the enemy, even these obsolete armored vehicles could be put to good use. In order to compensate for the lack of armored vehicles, both the Germans and the Partisans made a number of unusual modifications. These often included reusing the already existing vehicles and adding better weapons in the hope of increasing their firepower. Probably some of the best-known examples of this were the M3 Light Tank modifications made by the Partisan First Tank Brigade in late 1944. These were made by adding a 2 cm anti-aircraft or a 7.5 cm anti-tank gun on the M3’s superstructure.

The Germans were not idlers either, creating a number of lesser-known improvised armored vehicles. These were constructed by simply reusing any available vehicles. Some modifications were quite simple, like adding a machine gun on a civilian car or truck. Others were more elaborate, such as adding a Panzer 38(t) turret on an Italian medium tank’s body. Another modification included arming a Sd.Kfz.251 half-track with two 12 cm mortars.

Sd.Kfz.251

During the early development of new Panzer formations, it quickly became obvious that the supporting infantry would need a vehicle that was protected and also had sufficient mobility to keep up with tanks. The choice was made to use the already available Sd.Kfz.11 half-track chassis, on which an armored body was placed. Two firms were responsible for the creation of this vehicle, Hanomag and Bussing-NAG. The first was responsible for the development of the chassis, while the latter was to provide the upper body armor. This vehicle was designated as Mittlere Gepanzerte Mannschaftskraftwagen (Englis: Medium armored personnel vehicle), but is generally best known by its designation number, Sd.Kfz.251.
It had a crew of 2 but was capable of transporting a squad of 10 troops. It was lightly protected but provided with highly sloped armor plates. The armament consisted of two machine guns, one mounted to the front and the second to the rear. Production of the first vehicles began in 1939, and, initially, three different versions would be introduced to service (Ausf.A to C) each receiving a slight modification to improve the vehicle’s overall performance. From 1943 onwards, the Ausf.D was introduced to service. It offered a more simplified overall construction, which was better suited for production. Overall, by the end of the war, over 15,000 of all variants were built.

The Sd.Kfz.251 in Yugoslavia

The Sd.Kfz.251 was used for the first time in the Balkans during the occupation of Yugoslavia in April 1941. Following the successful completion of the short so-called April War (lasting from 6th to 17th April), most German armored formations either advanced toward Greece or went back to Germany to prepare for the upcoming invasion of the Soviet Union.

Until 1943, these vehicles were generally rarely used in fighting with the Yugoslavian Partisans. After the capitulation of Italy and the ever-increasing numbers of Yugoslav Partisans, the Germans began introducing a larger number of Sd.Kfz.251s. Some units that used the Sd.Kfz.251 or some of its variants during 1943 were the SS Freiwilling Gerbirgs Division Prinz Eugen and the Verstarkers Polizei Panzer Kompanie 13. Interestingly, the later unit also employed the rare VK16.01 Panzers. Probably the best-equipped unit that saw service by the end of 1943 was the Panzergrenadier Lehr Regiment 901. In total, it had 236 Sd.Kfz.251s in 10 different variants. This included some 10 Sd.Kfz.251/2s armed with a single 8 cm mortar. This unit was only stationed briefly in Yugoslavia, before being moved to Hungary. The Panzer Abteilung 202 operated in Yugoslavia through the war, and, by late 1944, had in its inventory a number of Sd.Kfz.251 vehicles. The Sd.Kfz.251 performed their original role, transporting troops, or other support roles, such as ammunition carriers, firing support, or command.

The Modified Vehicle

There are a few photographs showing Partisan crew members operating a modified Sd.Kfz.251 half-track. This half-track had its superstructure partly cut off in order to use the new armament of two heavy mortars installed inside its passenger compartment. Unfortunately, this vehicle is quite poorly documented and there is little-to-no information about its use. Even the reasons why it was built are unknown.

Who Built It?

Due to the general lack of any kind of information about its origin, it is difficult to determine who actually built this vehicle. There are few possible participants in the fighting in Yugoslavia who could have potentially done it.

The Axis’ Allies

Almost from the start, of Germany’s allies, Bulgaria and Hungary can be excluded as the builders of this vehicle. While they had ground forces stationed in Yugoslavia, none of them ever operated any armored element during the occupation period. This does not include the later Bulgarian involvement when they switched sides and helped the Partisans liberate some towns in Serbia. During this occasion, they employed German-supplied armored vehicles and even managed to capture some damaged vehicles left by the retreating Germans. While there is a small chance that they could have modified the Sd.Kfz.251, it is highly unlikely for a few major reasons. The participation of the Bulgarian forces in Yugoslavia was rather brief, near the end of 1944. They simply lacked the time and a proper workshop to modify this vehicle. Lastly, but more importantly, the Bulgarians took with them nearly all captured German vehicles that they came across. They even waged small skirmishes with the Partisans over them, resulting in casualties on both sides.
The other Axis ally, Croatia, was more reliant on Germany for its survival. Due to its inability to acquire weapons and armored vehicles, it was highly dependent on Germany in this matter too. In 1942, the Croatians did manage to locally build a few armored trucks. While they received some armored vehicles (excluding the Sd.Kfz.251) from the Germans, these were allocated in limited numbers. Based on their limited production capabilities and resources, they too seem unlikely to have modified the Sd.Kfz.251. Interestingly enough, there is a photograph of an Italian medium tank equipped with a German Panzer 38(t) turret which was often associated with the Croatians due to its markings. The history of this vehicle is unknown, but, given the fact the Croatian never operated either of these two tanks, it is likely a German modification, possibly temporarily given to their allies.

Yugoslav Partisans

The Yugoslavian Partisans made several improvised armored vehicles during the war. For example, the First Tank Brigade modified a number of Allied-supplied M3A3 tanks and equipped them with German-captured weapons (7.5 cm PaK 40 and 2 cm Flak 38 Flakvierling) in the Šibenik workshop during 1944/45. In addition, they also modified one Somua 35 by replacing its gun with the larger 57 mm gun taken from a damaged AEC II armored car. They certainly had the ability to make this modification. Given that the only surviving photograph of this vehicle shows it being operated by the Partisans also greatly supports this idea. On the other hand, there is no documentation that shows that they actually did it, unlike for the other known conversions.

Germans

The most likely creators of this vehicle were the Germans. There are several reasons for this. The vehicle and the gun were of German origin and their troops had the expertise, tools, and equipment needed to actually make such an improvised vehicle. Lastly, but most importantly, a number of authors, such as B. D. Dimitrijević and D. Savić Oklopne (Jedinice Na Jugoslovenskom Ratistu 1941-1945), mention that this vehicle was captured from the Germans.

There is another possibility that this vehicle was actually purposefully built by the Germans. In August 1944, Horch, the main producer of this vehicle, was instructed to develop a new vehicle armed with the 12 cm GrW 42 mortar. This mortar was to be positioned on a semi-rotatable baseplate located inside the crew compartment. During the prototype testing, it was noted that firing the heavy mortar generated a strong, albeit brief, recoil force of around 107 kg. Unfortunately, nothing else is mentioned in the sources. If these trials were successful, or if even any vehicles were built, is unclear. We do not know if there is any correlation between these two vehicles.

Designation

There is no information about the exact designation for this vehicle, and whether the Germans or later Partisans even bothered to assign one for it. In accordance with German army practice, the nomenclature, and designation of such a modification could have been Sd.Kfz.251 mit (English: with) Zwilling 12 cm Granatwerfer 42.

Design

Hull

The Sd.Kfz.251 hull consisted of a frontal mounted engine compartment, followed by the tracked suspension unit, above which the armored superstructure was placed. For this modification, it appears that the overall hull design remained unchanged.

Suspension and Engine

The Sd.Kfz.251’s tracked suspension consisted of seven overlappings and interleaved double road wheels, where the last one also acted as the idler. These were mounted on swing arms sprung by torsion bars. The suspension was powered by a front-mounted drive sprocket. The steering of the vehicle was done by the front-mounted wheels at low steering.
This vehicle was powered by a Maybach HL 42 100 hp@ 2,800 rpm strong engine. With this engine, the Sd.Kfz.251’s maximum speed was slightly over 50 km/h, limited to 30 km/h cross-country. With a fuel load of 160 liters, the maximum operational range was 300 km on road and 150 km off-road. The weight of the two mortars, machine guns, spare ammunition, and crew members would have probably slightly increased its overall weight of 8.6 tonnes. This, in turn, may have affected this modified vehicle’s performance to a small extent. Due to the lack of available information, it is difficult to know this more precisely.

Superstructure

While there are only a few photographs of this modified vehicle, none of them show the whole vehicle. This may lead to some problems with the identification of the precise version of the chassis. Luckily, one of the existing pictures shows the right side of this vehicle. On it, one major feature exists that helps identify the precise version of the Sd.Kfz.251 which was used as the base. The modified Sd.Kfz.251’s side shows that it had the three large storage bins, present only on the Ausf.D versions. Earlier versions had different bins, which helps identify the precise version.
The vehicle itself appears to have retained much of its superstructure unchanged. The major modification implemented was cutting the upper parts of the side armor. This was done to provide additional traverse for the main armament. If any other change to the superstructure was done is sadly not known.

Armament

Following the invasion of the Soviet Union in 1941, the Germans managed to capture large stockpiles of different kinds of weapons. This included the 12 cm PM-38 mortars. The Germans were quite impressed with this weapon and put it in service, where it was known as 12 cm Granatwerfer 378(r). Given this mortar’s excellent performance, the Germans even began their own production of this weapon, simply copying its design. The newly produced mortar received the new designation 12 cm Granatwerfer 42 (12 cm GrW 42), but was otherwise the same as the original Soviet mortar. When fully deployed for firing, its overall weight was 285 kg. The elevation ranged between 45° to 85°. The normal firing rate was 6 rounds per minute, but a more experienced and well-trained crew could increase it to 8 to 10 rounds per minute. With a muzzle velocity of 283 m/sec, the maximum firing range was slightly over 6 km.

The choice of using two large 12 cm mortars for the armament of this modification is unusual. Given the high trajectory of the 12 cm rounds during firing, it is obvious that it was designed to provide long-range artillery support. This concept was not new to the Germans, as they already employed the Sd.Kfz.251 vehicles in this manner. The Sd.Kfz.251/2 version was designed to provide the infantry with a supporting firing platform armed with one 8 cm mortar. The whole mortar, with its base and legs, was simply placed inside the crew compartment. No major modification was needed on the vehicle itself, besides the removal of the front mounted machine gun and some minor internal changes in order to fit the mortar with its ammunition.

The improvised vehicle employed in Yugoslavia was quite different in many regards. The most obvious change was the addition of two 12 cm mortars. This would require a number of structural modifications to the vehicle itself. In contrast to the 8 cm mortar, its larger counterpart used a larger round-shaped base platform. This provided a better firing platform and also prevented the mortar from digging itself into the ground during firing.

How the two mortars were installed inside this vehicle is unknown. Based on the surviving photographs, it appears that the mortar mounts were heavily modified. First, a sufficiently strong base platform had to be installed inside the Sd.Kfz.251’s bottom. This had to be strong enough to contain the recoil force of the two mortars without damaging the vehicle itself. If the 12 cm mortar platform was reused or a completely new one was built is unknown.
It appears that a new mount that held the two barrels was used instead of the original mortar bipod. As the photograph’s angle is not very good, it is also possible that the original bipods were retained with some modifications. Both the elevating and traverse screws, with their handles, were retained. Due to close proximity of the barrels, the traverse handles had to be positioned opposite of each other. This new installation appears to have provided an independent limited traverse and elevation of the two mortars. It is important to note that, as these two shared a common base platform, both barrels had to be pointed in the same direction. The different positions of the mortars on the available photograph and the cut upper side armor plates indicated that these may have had a full 360° firing arc.

The strange thing about this contraption is that no mortar sights are visible in the available photographs. These were originally located to the left of the mortar barrel. There could be several explanations for this. The simplest one would be that, due to photograph angles, the sights cannot not be seen. It is also possible that the crew that appears to be operating the mortars did not put them on. Lastly, it is also possible that the German crews took them with them just before the vehicle was captured by the Partisans, in order to disable it to some degree.

The ammunition load for the two 12 cm mortars stored inside is unknown. The Sd.Kfz.251/2 armed with a single smaller mortar had an ammunition load of only 66 rounds. This indicates that the ammunition load for two larger mortars may have consisted of a dozen or even fewer spare rounds.

Two of what appear to be MG 34 machine guns were added to the vehicle. These two were placed on small mounts, located on the front part of the side armor plates. The overall characteristics and the ammunition load of these are unknown. The rear-positioned machine gun mount was unchanged.

The installations of the two machine gun mounts are quite mysterious, as the range of the two mortars meant that the vehicle would only engage with enemy positions from a long range. Thus, it did not need to engage an enemy at close range, rendering the machine guns superfluous. It is also possible that the Partisans themselves added these to the vehicle, as the vehicle may have been used for propaganda to look more intimidating.

Armor Protection

The Sd.Kfz.251 was lightly protected. The frontal armor consisted of 14.5 mm angled plates and the sides were 8 mm thick. The bottom and the top were even weaker, at 5.5 mm. The armored plates used on this vehicle were well-angled, which in turn increased the chance of deflecting small caliber rounds. The small round opening on the superstructure sides would make this vehicle’s crew somewhat more exposed to enemy fire. But, given that this vehicle was meant to provide fire support from some distance away, this was not a major issue.

Crew

The number of crew this vehicle had is unknown. An Sd.Kfz.251/2, which was armed with the smaller 81 mm mortar, had a crew of 8. The modified Sd.Kfz.251, despite its larger armament, may have had a smaller crew. The vehicle itself would have needed the driver to drive it and also a commander. Given that it may have been possible to fire the two mortars independently, two gunners would have been needed. In addition, it is not clear who would operate the front-mounted machine guns. These were likely operated by the mortar gunners themselves.

The installation of the new armament and the ammunition needed to fire them would greatly have reduced the interior space. Likely, a loader had to be present to provide the necessary ammunition. It may also be possible that the gunners would also have served as loaders. This, in turn, would have greatly reduced their effectiveness and the vehicle’s rate of fire. Lastly, additional crew members would likely have been transported in another auxiliary vehicle that may have served as an ammunition transporter. Once again, given the general lack of any kind of information about this modified vehicle, this is just educated speculation.

Service and Fate

The usage of this vehicle by the Germans is unknown. What is known is that, at some point in early 1945, it was captured by the Partisans in Croatia. It became part of the First Tank Brigade, but its final fate or if they even used in combat is not documented. This should not come as a surprise, as the Partisans themselves kept very poor documentation of the usage of captured weapons. In a number of cases, the use of armored vehicles by some Partisan units was not even reported to their superiors. This meant that this modified vehicle may have seen action against its former creators. There is also a possibility that it was lost in combat fighting the Germans.

The Partisans and the new Yugoslavian People’s Army after the war made extensive use of captured enemy equipment, as nothing else was available. For example, they operated at least a few of the rare Sd.Kfz.251/22 version armed with the 7.5 cm PaK 40 anti-tank gun up to the early 1950s. If this mortar-armed vehicle indeed survived the war, it was likely scrapped shortly afterward.

The Mortar Armed Stuart M3 Tank?

It is somewhat confusing that the available sources (mostly on the internet) mention that the Partisan First Tank Brigade had modified one of their tanks, replacing the turret and adding a mortar instead. As there is no actual proof that this ever occurred, it is likely that the culprit for this confusion was this modified Sd.Kfz.251 vehicle. Given that the surviving photograph does not show the whole vehicle, it is easy to see that for an untrained eye could have easily misidentified this as a tank chassis. This has led to speculations that the Partisans modified one of their M3 tanks in this way.

Conclusion

This modified Sd.Kfz.251 was another strange vehicle built and possibly used in Yugoslavia. Its overall design is shrouded in mystery, as it is not completely clear what its creator wanted to accomplish. Why add such extensive armament consisting of two heavy mortars and possibly up to three machine guns? Unfortunately, due to a lack of any information about its use, it can not be said if it was successful or flawed as an improvisation. It is a mystery that will probably remain unsolved until, hopefully, someone digs out more information about its history.

Sd.Kfz.251 Ausf.D mit Zwilling 12 cm Granatwerfer 42 Specifications
Weight	8.5 tonnes
Dimensions	Length 5.92, Width 2.88, Height 2.7 m
Engine	Maybach HL 42 100 hp@ 2,800 rpm
Speed	50 km/h
Primary Armament	Two 12 cm Granatwerfer 42 mortars
Secondary Armament	Up to three machine guns
Armor	5 to 14.5 mm

Sources

T.L. Jentz and H.L. Doyle (2001), Panzer Tracts No.15-3 mittlerer Schutzenpanzerwagen Sd.Kfz.251 Ausf.C and D
B. D. Dimitrijević and D. Savić (2011), Oklopne Jedinice Na Jugoslovenskom Ratistu 1941-1945, Institut za savremenu istoriju
D. Predoević (2008), Oklopna vozila i oklopne postrojbe u drugom svjetskom ratu u Hrvatskoj, Digital Point Tiskara
V. Vuksić (2003), Tito’s Partisans 1941-45, Osprey Publishing
T. Gander and P. Chamberlain, Enzyklopadie Deutscher Waffen 1939-1945, Motor buch Verlag

T. Anderson (2021) Panzergrenadier Osprey Publishing