15/17 cm Sturmgeschütz auf Mausfahrzeug

German Reich (1944)
Assault Gun – None Built

The Maus is possibly one of the most recognizable tanks ever made, despite only two hulls ever being finished. The entire history of the development, design, testing, and construction of the heaviest tank ever built is a long and convoluted one stretching from early concepts in 1941 to a finished and operational vehicle in 1945. At nearly 200 tonnes, the Maus was an enormous machine, more than double the weight of any other tank and, as such, is often the butt of scorn for being too heavy or a waste of resources. Such criticism though is belied by the technical achievement in making this machine move under its own power and producing a vehicle with armor almost beyond the ability of any Allied tank-mounted weapon to penetrate. Of course, no tank can operate independently and wars are not fought and won by single tanks, so ideas of one-on-one tank comparisons between the Maus and something like a Sherman are not only fruitless and pointless but also completely disingenuous. Certainly, the Maus was not a military success, it saw no combat and was indeed the recipient of a lot of time and effort which could have been spent elsewhere in the German war effort. It may come as a surprise, therefore, that, despite just two hulls and one turret for the Maus being finished, it was proposed to use it as a base for another vehicle. Almost every German tank from the Panzer I onwards served as either a platform for an anti-tank gun or self-propelled gun. These vehicles were combat proven to be effective and were easier and cheaper to make than turreted tanks. It should be no surprise, therefore, that even the Maus project touched on this area at one point. The story of this improbable idea dates to May 1944.

Conception

An ever-popular topic with model and game companies are the ‘what-ifs’ of German tank evolution in WW2 and, with few exceptions, most tanks received a tank-destroyer version. That is that the hulls were repurposed for the mounting of a fixed superstructure on top with a forward-facing gun. The Maus too followed this direction in a very short-lived concept from May 1944.

The Maus project had actually already been canceled in November 1943 following severe production delays thanks to the Allied bombing of Krupp’s factory in August 1943. Despite this, the idea of restarting the Maus production program was being pushed by Dr. Porsche in March 1944 and he continued to press for this through the summer of 1944. Whilst the Maus program was finally re-killed in July 1944 with an order to scrap the remaining unfinished hulls (hulls 3 to 6), there had been a meeting held on 9th May 1944 which had offered some prospect of continuing Maus-related work. At that meeting, representatives from Porsche and Krupp met to discuss a new heavy type of self-propelled gun. This design was to revolve around the possible mounting of a 15 cm L/63 gun or the 17 cm L/53 gun on a heavily armored chassis to create a new heavy Sturmpanzer based on the Maus. Krupp, as before, would have responsibility for the production of the armor and fabrication of the hulls (obviously not the turrets as this would be a casemate-type vehicle), with Porsche being the design lead for the vehicle. Together, Porsche and Krupp had been two elements in the trio of firms that produced the Maus, the third being Alkett, which had responsibility for the assembly of the Maus. It is a fair assumption, therefore, that had this Maus-based vehicle ever gone ahead, Alkett would once more have been responsible for assembly. The entire vehicle-concept was intended as a competitor to the similar idea based upon the hull of the E 100 being developed at that time by the rival firm of Adler.

Post 9th May 1944

The idea might, in hindsight, seem impractical or even absurd to the casual observer, but this was not the case for Porsche and Krupp. They had met on 9th May and clearly, from that meeting, it was felt that this idea of using Maus hulls for this type of vehicle was a viable prospect. So much so in fact, that a follow-up meeting was held on 17th May to discuss what the new superstructure (casemate) for this Maus-hulled Sturmgescheutz would look like. This vehicle would therefore be known as (depending on which gun was mounted) either the 15 or 17 cm Sturmgeschütz auf Mausfahrzeug.

It was during this meeting that Krupp was adamant that they only wanted to use the 15 cm L/63 gun, presumably because of the weight and size of the 17 cm L/53 and its ammunition. Krupp was obviously being very serious about the significant challenge to fit this enormous gun onto an admittedly enormous chassis, but one which was already absolutely crammed full of automotive components and where any available space inside the lower hull was used for ammunition stowage.

However, Dr. Porsche, it seems, was slightly less realistic and completely ignored the enormous size of the machine once more. Just as he had done with the original Maus turret development, he proposed a secondary turret mounting a 3 cm anti-aircraft gun (3 cm Flak-Turm) to provide air-defense for the vehicle. This idea was immediately discounted, as the vehicle would be escorted by air-defense vehicles, would be out-of-gauge for travel by rail, and would interfere with the breech of the main gun.

That idea was not accepted and nor was the Porsche/Krupp plan for using the Maus hull design either. The hull was too high and too heavy compared to the E 100 hull. Instead, Krupp was contracted to produce a model for a 17 cm gun-carrying design based on the E 100 chassis instead. With that contract, issued on 28th May 1944, there was literally no reason for Krupp to continue working on a Maus proposal and the idea was dead.

As it turned out, the E 100-based idea did not fare much better either. If there were any lingering doubts on the matter, both concepts were over by the middle of the year after a meeting with General Guderian where he was shown the models. Guderian already disliked the Maus and had tried to kill that project by canceling all serial production, so the likelihood that he would agree to a new and heavier vehicle based upon one he already disliked was exceptionally unlikely. As could be expected, no further discussions or work on the project took place after this.

In total, therefore, this most unlikely of projects lasted from 9th May to no later than 28th May, 19 days in which to consider what a poor design choice it would be regardless of any consideration of what purpose this enormous vehicle was going to be put to. No drawings of the ideas from Krupp and Porsche survive for this project, if indeed anything more than a sketch was even prepared. What such a machine could have looked like is one of those essentially fruitless exercises in ‘what ifs’ so beloved by computer games and model makers but, aside from shamelessly exploiting an interest in ‘exotic’ German armor for commercial purposes, there are real questions to be asked of what any design could have looked like.

Layout

The primary consideration over what a 15/17 cm Sturmgeschütz auf Mausfahrzeug would have looked like starts with the hull. Obviously, the hull selected was that of the Maus and, given the incredibly tight space in which to operate the mechanisms of the hull, there appears to be no prospect for moving the engine, generators, or motor components around inside the hull. On top of this, any rearrangement of drive components etcetera would change the shape of the hull and the armor layout etcetera to such an extent that this vehicle’s hull would be very different from that of the Maus. Given that the name is ‘15/17 cm Sturmgeschütz auf Mausfahrzeug’ – an assault gun based on a Maus hull, any interpretation of the layout must begin with a look at the Maus hull.

The Maus hull should be considered as existing in four sections. Right at the front, in the center, is the driver’s compartment housing the driver and radio operator under a single ovaloid hatch. Behind this was a large section for the engine and air intakes for cooling the engine and electric motors. It was on this section that three large shell deflectors were fitted to protect the grills. Behind the engine section is the turret area defined by four plates cut and welded together to form the opening for the turret basket and ring. More automotive elements were below this area.
Finally, at the back, there was another section of grilles out of which warm, spent air was forced out having been drawn through the vehicle to cool the engine.

What this layout means is that there could only be one place to mount a casemate for the gun for the vehicle, the area previously occupied for the turret. Removal of the 60 mm hull roof armor and turret ring at this point would provide the space for the casemate, although this would mean that the gun was mounted behind the engine. This was not generally favored for a vehicle as it caused numerous problems, such as access to the engine area for maintenance. It would also mean a relatively small amount of depression would be available. Nonetheless, there was simply nowhere else it could go without a complete redesign of the hull. If the casemate was limited to just the space between the vents on the hull it would also not be long enough for the enormous gun breech. Although no drawings of this idea survive it is perhaps logical to consider that a realistic solution to expelling this air could have been found in a similar manner to that on the Elefant/Ferdinand tank destroyer – by venting air out of the rear of the hull plate under the fighting chamber but without the drawings or a description this is purely speculative.

Armor

The next question which would arise would be the armor on the vehicle and this is easier to resolve. The armor for the Maus hull is already well documented and knowing where the casemate would have to go would create a casemate behind the engine. The face of this casemate would have to match or exceed the armor value of the front of the hull which was 205 mm angled back at 55 deg. The Maus hull was designed as 200 mm but, due to manufacturing tolerances, was measured as 205 mm in a post-war British examination. Assuming the same basis was to match 200 mm at 55 degrees, this would mean an effective armor of 283 mm line-of-sight thickness.

Assuming the front of the Maus-casemate would match that of the Jagdtiger (probably the best analog of this general design concept – 250 mm at 15 degrees = 259 mm) it would require a front plate sloping back at about 15 degrees with about 273 mm of thickness, or, at 30 degrees a plate 245 mm thick. On the Jagdtiger, 250 mm at 15 degrees was already more than adequate for the task. It is perhaps more realistic to assume a rough equivalency to that layout but with a front sloped perhaps more like adopted and favored by Krupp for the Maus II and E 100 turrets.

Regardless of whether or not the actual armor had ever even been fleshed out on paper or not, the front of the casemate would have to be substantially well protected, just as would the sides. The Maus hull sides, in order to meet rail gauge requirements, were 173 mm thick and vertical but the turret sides for the 15/17 cm Sturmgeschütz auf Mausfahrzeug could not be vertical as this would prevent it from fitting through rail tunnels. Indeed, the Maus had to have a special railcar designed for it to not only take the weight, but to also lower the height when being shipped by train so it could fit through a tunnel. As the Maus with a turret already was at the limits of the German rail gauge, there is no space for the casemate on top of a Maus hull to get either wider or taller, so therefore must have followed roughly the same dimensions and angles as the turret. That would mean sides sloping towards the roof at an angle of about 30 degrees, presumably at least the same thickness as the lower sides (173 mm) and possibly as thick as the Maus turret sides were (200 mm). The rear of the casemate is more complicated, as there is more room to create an overhang over those rear air exhausts. Armor could be reasonably assumed to be in line with the Maus, as would the roof. The shape and size of the casemate are simply dictated by the limitations of the hull already crammed with the drivetrain, and by the fixed restrictions imposed by the rail gauge. The biggest issue for the design was not the shape or position of the casemate, but the fitting of the gun.

Gun

There were only two guns in consideration for the 15/17 cm Sturmgeschütz auf Mausfahrzeug and, as the name makes clear, these were a 15 cm or 17 cm gun. Krupp was adamant that he would do anything to avoid having to use the 17 cm gun. That 17 cm Sturmkanone (Stuk – assault gun) was 53 calibers long (L/53), longer than the 17 cm Kanone 18, and is often referenced online as being the same gun as planned for the Grille 17 (Geschützwagen Tiger für 17 cm Kanone 17 (Sf.)), although that gun was an L/50 rather than the L/53 (3 calibers / 51 cm shorter) optioned for this design. The 17 cm Stuk. L/53 existed only on paper as of 22nd March 1944.

It is likely that the reason for Krupp’s desire to avoid the 17 cm gun was the sheer size of it as well as the weight, over 7 tonnes, the length (over 9 meters), enormous breech, and very large and heavy ammunition. Mounting and balancing such a heavy gun was no small task and that is before considerations over the speed of loading it in the tight confines inside the casemate, a task likely to require at least two loaders.

That 17 cm gun though, like the 15 cm L/63, had to meet a specific requirement set in April 1944 by General Guderian (Inspector General of Panzer troops) to be able to defeat up to 200 mm of armor at 4,000 meters, leaving no doubt as to a key intended purpose of this vehicle – the destruction of increasingly well-armored enemy tanks at long range. The focus was on this ‘smaller’ gun, as work had already been done on a 15 cm gun mount for the Maus when that gun was considered more suitable for the delivery of a heavy high explosive round to destroy concrete gun emplacements as well as for taking on enemy tanks with armor-piercing ammunition. The 15 cm Stuk L/63 would also be a very large gun but was at least manageable. Both the E 100 and Maus were planned to be able to mount a 15 cm, although the longest 15 cm gun contemplated for the Maus turm was the 15 cm KwK. L/40. It is likely that neither of the planned guns, either the 17 cm L/53 or the 15 cm L/63, were actually made and so obtaining data on their performance and ammunition can only be inferred from scraps of available data.

The gun mounting for that 15 cm gun in the Maus turm was internal, that is the trunnions for the gun were behind the front armor of the turret. That turret had a serious potential flaw which was highlighted by Krupp, as the bottom half curved downwards and risked deflecting an incoming shell into the roof. This was highlighted in May 1943 by Porsche and the result was that, by the time of the Maus II turret in March 1944, it was to be replaced with a new, slope-fronted turret made from a single flat plate. That design change would obviate the problem of a deflected shot hitting the hull roof but it had also meant a larger turret ring and that the gun’s trunnions had to be moved onto the outer-face of the turret to cope with the new shape. That new gun mounting on the outside on the turret face would be repeated for the E 100 turret and here, importantly, would have to be repeated for the face of the 15/17 cm Sturmgeschütz auf Mausfahrzeug.

Once it can be logically established that the casemate would follow a certain shape, and that, in order to mount the gun on that casemate, it had to follow the same design process, then other parts of what the 15/17 cm Sturmgeschütz auf Mausfahrzeug could have looked can be speculated. Firstly, the secondary weapon. The Maus, Maus II, and E 100 all had a primary and a secondary gun, such as the 12.8 cm paired with a 7.5 cm, but for the 15/17 cm Sturmgeschütz auf Mausfahrzeug no such arrangement was either needed nor suggested. The Maus had its two guns mounted side by side, which caused enormous problems with space in the turret. One improvement on the Maus II was to stack these guns on top of each other, freeing up internal space albeit at the price of some gun depression.

With no secondary gun needed, the 15/17 cm Sturmgeschütz auf Mausfahrzeug could avoid both of those issues and would also have more space for ammunition which was significantly larger than the already large 12.8 cm shells on the Maus. Next, a machine gun. Both Maus and Maus II were to use a machine gun (MG.34 or MG.42) mounted on the left of the turret face and, although there is no mention of this weapon, it would appear extremely unlikely that one would not be considered for this vehicle too.

Finally, the range finder. The Maus was fitted with a rangefinder and this was improved with the Maus II by means of 2.1 m wide coincidence-type rangefinder across the roof of the turret. Later, this was to be further improved with a slightly narrower (1.9 to 2 m wide) rangefinder of the same type. There is no doubt that the 15/17 cm Sturmgeschütz auf Mausfahrzeug would have to have a rangefinder, especially given the 4,000 m ranges at which it was going to be expected to deliver accurate fire against enemy tanks and structures. Given the common positioning of the rangefinder on the Maus II and E 100, it is reasonable to assume a similar arrangement of a similar size/type of rangefinder would also have to have been used on the 15/17 cm Sturmgeschütz auf Mausfahrzeug.

Crew

Obviously, it is not possible to determine exactly how many crew would have worked a vehicle that never even made it to the drawing board, but there is also scope here to consider the number of men needed to operate such a machine. The Maus, for example, required a crew of 6 men. A driver and radio operator in the front of the hull, followed by a commander, gunner, and two loaders.

Based upon the Maus hull, the 15/17 cm Sturmgeschütz auf Mausfahrzeug would be unlikely to have changed the front crew section, as this was fixed into the hull. That would mean the driver and front radio operator would likely be the same. In the casemate, where the turret would previously have sat, the rest of the crew would be situated. This would have to include a commander, and a gunner making for at least 4 crew at a minimum. The gun obviously also required loading and thus, at least one loader would be needed. On the Maus, a second loader was retained as it had two guns and the shells were heavy and hauling them around would tire a single loader. Whilst the 15/17 cm Sturmgeschütz auf Mausfahrzeug likely had no secondary gun to be served by a loader, the 15 or 17 cm shells were huge and heavy. A unitary (one piece) 15 cm shell, for example, weighed in excess of 34 kg and possibly over 40 kg depending on what ammunition might have been chosen. Moving those shells around would rapidly exhaust a single loader, so a second loader is almost essential just to make the machine viable. This would be aside from any loading assist systems which might have been considered, which theoretically could have reduced the crew to just a single loader.

Conclusion

Although the idea of the 15 cm or 17 cm gun using the Maus chassis had failed after a brief spark of interest in May 1944 with the E 100 being selected in preference, it was not much of a loss. The E 100 was to suffer the same fate by the middle of July, with Hitler stopping the development of such enormous and heavy weapons. The 15/17 Sturmgeschütz auf E 100 fahrzeug, therefore, joined a long list of failed and abandoned Nazi projects.

Because it is not known what the 15/17 cm Sturmgeschütz auf Mausfahrzeug looked like, much of this article has been speculative about the shape and look of the vehicle. No firm drawing were ever even produced and no initial sketches are known to survive. Nonetheless, the speculation over its appearance is more than just idle chatter, but a serious effort to consider the problems the designers and builders would have faced and the solutions open to them. At times, such speculative contemplation has been taken to ludicrous extremes by game companies or model makers, but the 15/17 cm Sturmgeschütz auf Mausfahrzeug was still a very real idea. In hindsight, it may have been useless as a weapon and a waste of resources for the German war effort, but the idea was still made and seriously considered.

15/17 cm Sturmgeschütz auf Mausfahrzeug specifications
Dimensions	estimated 10.085 m long (9.034 m without gun), 3.7 m wide (series max.), estimated 3.649 m high
Total weight, battle-ready	estimated 188 to 200 tonnes
Crew	5-6 (commander, gunner, 1 or 2 loaders, driver, radio operator)
Armor	Turret Casemate Front – estimated 250 mm at 30 degrees Sides – estimated 205 mm at 30 deg. Rear – estimated 205 mm at 10 deg. Roof – estimated 60 mm at 90 deg.Hull Front – Glacis – 205 mm at 55 deg. – Lower front – 205 mm at 35 deg. Track guards – 100 mm at 10 deg. Sponson floor – Front – 50 mm at 75 deg. Sponson floor – Middle – 50 mm at 90 deg. Sponson floor – Rear – 50 mm at 85 deg. Side – Upper – 173 mm at 0 deg. Sides – Lower (skirt) – 105 mm at 0 deg. Side hull inner – 80 mm at 0 deg. Rear – Upper – 153 mm at 40 deg. Rear – Lower – 153 mm at 30 deg. Floor – front – 100 mm at 90 deg. Floor – middle and rear – 50 mm at 90 deg. Roof – Front – 103 mm at 90 deg. Roof – Middle – 60 mm at 90 deg. Rof – Rear – 60 mm at 90 deg.

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