The Bär self-propelled mortar amid the ruins of a German city in the final stages of the war; background: internet (public domain), plastic model: Canuck2016 (uamf.org.uk), composite: Panzernet

Fighter for the City

The Bär self-propelled mortar belongs among those German fighting vehicles that never progressed beyond the drawing board. That the Bär was never actually built is known for certain; the answer to when the effort to build it even began is rather less clear. Available sources differ quite significantly on this point. According to some authors (G. Parada and J. Ledwoch), the first proposal for a heavy self-propelled gun with a 305 mm gun appeared as early as May 1942. T. Jentz, on the other hand, states that Krupp did not submit its first design for this vehicle until March 1943. The later of these two dates fits the overall historical context considerably better. At the end of August 1942 the German 6th Army had reached the outskirts of Stalingrad, and in the weeks and months that followed it experienced the brutal reality of fighting in streets, factories, buildings and cellars. It was a type of combat for which German troops were neither accustomed nor prepared — and one that brought very specific problems, such as the need to dislodge defenders who had fortified themselves inside large multi-storey buildings.

Driving defenders out by room-to-room fighting inside a building was a slow process that also came at an enormous cost in casualties. The most effective way to overcome this kind of resistance was simply to destroy the entire building. But how to achieve this in practice? Sending combat engineers to the building with demolition charges was tantamount to sacrificing them. German tanks could approach a building with relative safety, but even at their best their guns were simply not capable of bringing down a large residential block or factory hall. Heavy artillery, which would certainly have been sufficient for the task, operated from great distances and was not accurate enough to take out a specific structure without destroying everything around it. Air power was of course also an option — a dive bomber could strike a designated building with a fair degree of precision, but this was a costly and time-consuming solution. Moreover, when attacking at low altitude over a city there was a considerable risk of being shot down by ground-based anti-aircraft defences.

What the German soldiers fighting in Stalingrad simply lacked was a self-propelled weapon capable of bringing down a large building with just a few shots, while at the same time withstanding close-range fire from enemy infantry weapons. The new fighting vehicle did not need to be fast, nor did it need a great range; what mattered above all was maximum firepower and robust all-round armour protection. In time, the general term Sturmpanzer came to be used for this specific category of self-propelled gun.

A knocked-out Bär mortar amid the ruins of a city captured by the Red Army; background: internet (public domain), plastic model: Canuck2016 (uamf.org.uk), composite: Panzernet

Krupp vs. Alkett

The soldiers' requirement for the development and production of such a weapon was conveyed to the Army High Command at Hitler's conference on 20 September 1942. The requirement was evidently considered sound and handed to the Berlin firm Alkett (Altmärkische Kettenwerk) for implementation. Alkett promptly prepared two new armoured vehicles, both designed specifically for the purpose described. The first of these, already in October 1942, was the Sturminfanteriegeschütz 33, built as a rapid stopgap solution with only 24 examples produced. The second and considerably more refined vehicle appeared in April 1943 and entered history under the unofficial combat name Brummbär. The Brummbär was not, however, destined to remain the pinnacle of the Sturmpanzer development pyramid. Already in May 1943 Alkett was working on an even heavier vehicle based on the Tiger tank chassis and armed with a 380 mm rocket launcher.

It was around this time, according to some authors, that Krupp entered the scene with a competing proposal for a heavy Sturmpanzer armed with a 305 mm gun. On 4 March 1943, Krupp was said to have presented army representatives with its first conceptual design, and by 10 May of the same year specific drawings were also on the table. The vehicle's chassis was to make use of various components from the Panther and Tiger II tanks (the latter still in development at the time). The powerplant of the new armoured vehicle was to be the thirsty but proven Maybach HL 230 P30 petrol twelve-cylinder engine with a displacement of 23 litres, producing a maximum output of 700 horsepower at 3,000 rpm. The Zahnradfabrik AK 7-200 gearbox with seven forward gears and one reverse was taken from the Panther. The Henschel L 801 steering unit for controlling the tracks when turning came from the then-in-development Tiger II. The road wheels, idler wheels and drive sprockets were also taken from this tank. The suspension system, however, was not — and indeed could not be — adopted from the tank, for a reason that will be explained below.

Vehicle Description

The self-propelled gun under development was given the easily memorable name "Bär" — meaning bear. Its chassis was to have ten axles on each side for interleaved road wheels. These were all-steel, fitted only with a thin rubber tyre concealed beneath a steel rim. Torsion bar suspension — the standard solution on heavy German vehicles, including the Tiger II — could not be used here. Conventional torsion bars ran transversely across the floor of the hull tub. The Bär's designers, however, needed to create a large opening in the hull floor for the gun's recoil travel, and that was incompatible with torsion bars.

This drawing of the Bär self-propelled mortar clearly shows the internal crane for handling shells and the gun's recoil travel into the open floor section, source: Flickr.com, edited

The vehicle's hull was to have a sloped front plate 130 mm thick. Some illustrations show a hull machine gun embrasure in the front plate, but the Krupp drawing from November 1944 shows no hull machine gun (though it is a very simplified drawing). The hull sides were to be 80 mm thick. The driver and radio operator had their stations in the front section of the hull, each with their own overhead entry hatch. Behind them lay the engine compartment, with the engine itself mounted centrally and the radiators on either side. The gearbox was located between the driver and the radio operator.

Armament

At the rear of the hull was the fighting compartment, with a rounded front wall featuring a large opening for the gun barrel. The vehicle's armament was to consist of a heavy 305 mm mortar with a barrel length of 16 calibres. This was to be a modified (and lengthened) version of the originally Czechoslovak vz. 16 mortar from Škoda Plzeň. The weapon itself weighed approximately 8 tonnes, its mounting a further 6 tonnes, and the massive rounded gun shield 2.5 tonnes. The mounting allowed the mortar to vary its vertical elevation from 0° to +70°, though lateral traverse was only 2 degrees to each side. The weapon was to use two types of ammunition: the high-explosive fragmentation Sprenggranate, weighing 350 kg, left the barrel at 355 m/s and could reach a target up to 10.5 km away; while the armour-piercing Betongranate, weighing 380 kg, had a muzzle velocity of 345 m/s and a maximum range of 10 km.

Firing such a heavy weapon produced an enormous recoil force, which had to be absorbed by a recoil stroke of a full 100 cm. This brings us gradually to the explanation of why the designers needed to create that large opening in the hull floor. A mortar is by its nature a weapon designed to destroy fortifications, and it typically fires at high elevation angles so that the shell arrives at the target from a steep trajectory, thereby gaining high velocity and energy on impact. It was precisely when firing at a high angle that the long recoil stroke became a problem, because after the shot the breech would slam into the floor of the fighting compartment. In theory the problem could have been solved by mounting the weapon on a taller carriage, but this would have pushed the already enormous overall height of the vehicle even higher. The other theoretical solution — lowering the floor of the fighting compartment — would in turn have reduced the vehicle's ground clearance and therefore its cross-country mobility. The designers therefore came up with the idea of an openable floor section. A portion of the floor at the rear of the fighting compartment could be lowered all the way to the ground, and it was into this space that the barrel was to recoil when firing.

Rear view of the Bär self-propelled mortar — note the crew access doors; background: internet (public domain), plastic model: Canuck2016 (uamf.org.uk), composite: Panzernet

The Bär self-propelled gun was designed to be 8.2 metres long, of which 5.3 metres was the ground contact length of the tracks. With a track gauge of 3.1 metres, this gave a not particularly comfortable turning ratio of 1.71. The track contact length when sinking 20 cm into soft ground (i.e. off-road) increased further to approximately 5.9 metres, worsening the ratio relative to the track gauge to 1.9. Two types of tracks were planned for the vehicle: combat tracks 100 cm wide and transport tracks only 50 cm wide. The transport tracks were used when travelling by rail, so that the vehicle fitted within the prescribed loading gauge limits. The Bär was designed to stand 3.55 metres tall and 4.1 metres wide with combat tracks, or 3.27 metres with transport tracks. The firing height of the mortar was 2.4 metres. The vehicle's total combat weight was calculated at 120 tonnes, and its maximum speed was expected to be around 20 km/h. With the wide combat tracks fitted, the ground pressure (the figure derived from the ratio of weight to the track contact area with the ground) was expected to be around 1.02 kg/cm² (assuming 20 cm of ground penetration).

The vehicle's crew was to consist of six men. In addition to the already-mentioned driver and radio operator in the hull, there were a commander, gunner and two loaders in the fighting compartment. Two hatches in the roof of the compartment served as the crew's entry and exit points; their covers were to be fitted all around with observation periscopes. A large opening in the rear wall of the compartment would probably have been provided for ammunition loading. Given the shell weights quoted above, it is clear that loading the gun could under no circumstances have been purely manual work. A simple overhead crane was therefore to be suspended from the roof of the fighting compartment to assist with ammunition handling. Only 10 shells could be stowed on board, after which the Bär had to replenish its ammunition from a supply vehicle. In practice, those 10 rounds were not quite as meagre a supply as they might seem. The rate of fire was very low, since after every shot the barrel had to be depressed back to the loading position, and the handling of the shells themselves was also a fairly slow process. The risk of the Bär running out of ammunition too quickly was therefore decidedly remote.

End of the Project

From the specifications outlined above it is clear that the Bär self-propelled mortar would have been a truly monstrous weapon, and it is therefore not particularly surprising that it never entered production and that not even a prototype was built. The Bär lost an unannounced competition to the Alkett vehicle that would later become known as the Sturmtiger — which was, for the record, only marginally less monstrous than Krupp's Bär.

ARTICLE
CONTENTS:

FIGHTER FOR THE CITY

KRUPP vs. ALKETT

VEHICLE DESCRIPTION

ARMAMENT

END OF THE PROJECT