Nazi Germany (1944)

SPG – 18 built

Of all of the heavy tank projects from Germany in WW2, one vehicle stands out as something very different from the others and drew significant curiosity from the Allies when they first encountered it. A vehicle combining the armor of a heavy tank with a weapon never fitted to an armored fighting vehicle before, a 38 cm mortar. This incredible vehicle was developed for a specific purpose, urban combat. In such a situation, a huge shell could demolish whole buildings and defensive structures. It could deliver a huge explosive shell at close quarters or be used for long range shelling of an enemy position. That vehicle was the German Sturmtiger.

The origins of the Sturmtiger, or, more correctly, the ‘38cm RW61 auf Sturmmörser Tiger’, started with a call from the German Army (Heer) for a heavy howitzer specifically to help in urban combat, where a well-defended building could hold up an attack or otherwise be resilient against even ‘normal’ caliber artillery fire. What was needed was a gun capable of firing a large explosive shell both directly and indirectly and to have it mounted on a heavily protected chassis. This call was put into reality by Hitler on 5th August 1943, following the failure of other ideas for high-angle guns mounted on tank chassis.

Prototype to production

Despite Hitler’s order to develop a vehicle being issued in August 1943, only one prototype was initially ordered, possibly indicating how much confidence there actually was for such a weapon. Nonetheless, a vehicle was put together based on the chassis of a Tiger tank by the firm of Alkett in Spandau, using an armored superstructure built and assembled by the Brandenburg Iron Works (Brandenburger Eisenwerke) at Kirchmöser. The vehicle was ready and was shown to Hitler at the Ayrs Training Camp in East Prussia on 20th October 1943, an impressive turn-around time of under 3 months.

Despite the impressively rapid construction of a prototype, mass production was severely hampered by the slow rate of manufacturing of Tiger I tanks and was not due to start until mid-1944. Any production of Sturmtigers alongside the Tiger I would have impeded Tiger I production. Since priority was clearly given to the Tiger I tank, the Sturmtiger had to wait. In the meantime, the prototype was undergoing testing and trials.



Prototype Sturmtiger with rubber-tired road wheels. Note: this vehicle is in the possession of the Russian collection at Kubinka with steel-rimmed wheels and the steel counterbalance on the muzzle of the mortar – two later modifications, although it retains the uparmored lower front hull. Source Spielberger. The top image has been colorized by Jaycee ‘Amazing Ace’ Davis.

By May 1944, the Sturmtiger prototype had been kept busy with trials and firing tests for the development of range tables, but production had still not started and the concept was likely to be scrapped. Rather than ditch the idea though, Hitler ordered that, instead of interrupting the production of the Tiger I, the Sturmtigers would be built on the chassis of Tiger I tanks which had already been in action and suffered serious damage. These were being sent back to the factory for rebuilding rather than just for repair. Twelve Sturmtiger units were to be prepared. A Tiger I cost RM250,800 (Reichsmarks) each to build, but as these Sturmtigers were made from rebuilds, it is not possible to calculate the cost of the rebuilding of each hull as each vehicle used had suffered a different amount of the damage. Even so, the cost of building a Sturmtiger was estimated at RM53,000, which, if added to the RM250,000, means that each one constituted an investment of over RM300,000 (approximately US$4,255,264 in 2015 values). This was an enormous sum of money considering it cost just RM117,100 (approximately US$1,660,971 in 2015 values) for a Panther tank.*

*RM to US$ exchange values conducted using Historical Statistics

Twelve Sturmtigers were built which, with the prototype, makes thirteen Sturmtigers finished by the end of September 1944. Five more were ordered by Hitler on 23rd September 1944. Those additional five vehicles were all finished by the end of December 1944, followed by orders for more, although these were never produced. In total, 18 Sturmtigers were built.

Running gear

The running gear for the Sturmtiger was identical to that of the Tiger I with the exception that only the prototype had the rubber-tired wheels. The production Sturmtigers were supposed to be fitted with the rubber-tired road wheels to help manage the additional 8-tonne load of the Sturmtiger over that of the Tiger I, but they all are seen with the steel-rimmed wheels common to late Tigers. The rubber-tired wheels are one of the identification features of the original prototype Sturmtiger, even though even these were later changed to the steel-rimmed wheels. The engine remained the same as on the Tiger I, a Maybach HL 230 TRM P45 and, with the additional weight, the Sturmtiger was markedly slower and less maneuverable than the Tiger I. If a later production damaged Tiger I tank was used to build a Sturmtiger it would be powered by the more powerful Maybach HL 230 TRM P45 V-12 700 hp petrol engine.

Armor and Optics

The lower hull of the Sturmtiger was that of the Tiger I and remained unchanged. Nominally, the armor on the Tiger I consisted of a lower front hull plate 100 mm thick, a short glacis 60 mm thick and a reclined driver’s plate 100 mm thick. The sides were a uniform 80 mm thick and vertical on both lower and upper section, and 80 mm thick on the back. Due to manufacturing tolerance allowance of 0 to +5%, many of these plates ended up being recorded as slightly thicker i.e. 102 mm instead of 100 mm.

For the Sturmtiger, the turret was removed, as was the roof of the hull over the fighting compartment. Further, the driver’s plate was mostly gone, with the top half of it cut-off across the full width. Replacing all of this was a large flat-sided box containing all the crew and the main gun. The front of this box was made from a single slab of armor plate 150 mm thick angled back at 45 degrees which extended down to a point about halfway along the length of the glacis. It was held to the front of the hull by two substantial armor plates bolted over the joint. In the front of the plate was a large, armored ball-mount 69 mm thick for the 38 cm mortar and a small ball-mount for the forward-firing M.G.34 machine gun. The gun and mount were also protected by a 150 mm thick mantlet. On the left of the gun was a rectangular opening which took the aiming telescope and, below this, a pair of small visors under a small cowl were placed for the driver. The sides and rear were made from slabs of armor 80 mm thick but angled inwards towards the roof, which was 40 mm thick. On the prototype, an additional 50 mm thick slab of armor was bolted to the lower front hull of the Sturmtiger, but this feature was dropped from production vehicles, presumably to save weight.



Armor scheme for the Sturmtiger which omits the remnants of the bottom half of the driver’s plate and top part of the glacis which would lie just behind the bottom edge of the 150 mm thick front plate on the Sturmtiger. This scheme also omits the armored mantlet around the gun barrel. Source: Wikipedia



View of the driver’s station at the front-left of the Sturmtiger clearly shows both his vision optics but also that the original glacis was left intact and the original driver’s plate was simply cut off lengthwise for the new front plate. Source: Schneider



Seen from the outside, it is clear that the new front plate significantly overlaps the old armor on the front of the Tiger. The thick block of armor on the corner is there to cover the overlap between the new casemate and the hull. The bolts on the side indicate a reinforcing plate added on the inside joining the two sections together. Source: Schneider

Sighting for the mortar was by means of a Kugeloptik ZF3 x8 sight using the aperture to the left of the main gun and a KgZF2 sight. Other features included the pistol ports on both sides, perhaps more useful for aiding vision than the original intention for them.



Overhead view of a Sturmtiger showing the large rectangular roof hatch used for reloading. Source: The Tank Museum, Bovington

The gun

Originally, the request from the Army called for a 210 mm howitzer but, with no suitable options, they turned to Rheinmetall-Borsig for their Raketenwerfer 61 L/5.4 (Gerat 562 – Sturmmörserwagen 606/4). The gun itself existed in two iterations at the time. One, the R.aG 43 (Raketenabschussgerät 43), was a ship-mounted anti-aircraft weapon used for firing a cable-spooled parachute-anchor creating a hazard for aircraft. The second, the RTG38 (Raketen Tauch Geschoss 38), was a land-based system. Both systems had been made by Rheinmetall-Borsig, in Dusseldorf, but had been designed by MOHRA Gerätebau Aktiengesellschaft Bautsch of Ostsudeten. It was the RTG38 which formed the basis of the weapon in the Sturmtiger. With a range of 3,000 m, it had originally been planned for use in coastal installations by the Kriegsmarine firing depth-charges against submarines. For use in a vehicle, it was to find use as a demolition gun and had to be modified for that role. This modification work was carried out by Rheinmetall at their Sommerda works.

In its coastal defense role against submarines, it was not an effective weapon, and only 12 were made, of which 3 were tested in 4th April 1944 at Trondheimsfjord, Norway. The result was that problems were identified with the fuzing and the rounds failed to achieve the ranges (up to 3,000 m) desired. A second test firing, held on 20th April 1944, revealed an 18% failure rate, likely due to problems encountered when the shell hit the water. Instead, the weapon was selected for use against surface targets and they were based in positions at Fanø Island, Denmark (1 weapon based on the Marine Küsten Batterie Gneisenau) and at batteries at Alta, Agdenes, and Trondheim in Norway (unknown numbers). Two of these weapons are preserved in museums in Copenhagen (Denmark), and Tromsø (Norway), respectively.



R.aG43 at the Tøjhusmuseet in Copenhagen, Denmark, marked ‘bwo 38cm R.ag.M43 Nr.10’ (left). Unconfirmed RTG38 (possibly a modified RaG43) at the Narvik War Museum (right), the example in Norway appears unmarked or illegible. Source: Massimo Foto on Landships (left) and Yetdark on Flickr (right) Further research on these guns is needed.



Believed to be a R.aG43 on a land mount for coastal defence in Denmark or Norway. Source: Axishistoryforum.com

Modified for use in a vehicle, the recoil from the modified rocket-mortar was enormous, about 40-tonnes, and this meant that only a heavy chassis could be used to mount the gun. The only suitable vehicle in Autumn 1943 was the Tiger I.

Some of the gun barrels were modified during production with a heavy steel ring around the muzzle as a counterweight to make elevation easier but, other than the mounting, the gun was effectively the same principle as before. The shells for the weapon were extremely heavy, far too heavy for a man to load manually, at 330 kg each. As a result, each of them had to be carried by means of a ceiling-mounted trolley from their rack to a roller-mounted tray at the breech. Once on the tray, four soldiers could then push it into the breech to load it. The whole process took 10 minutes per shot from loading, aiming, elevating to firing.



Breach of the RW61 with shell absent (left) and being loaded, providing a good view of the vents on the bottom of each shell (right). Source: Schneider (left), Navweaps (right)

The rounds were huge and only 12 rounds could be carried internally on the 6 racks provided, stacked three high and two deep on each side. No special resupply vehicle was provided to carry additional shells but additional shells could be carried in trucks by the unit, which would allow the Sturmtiger to be reloaded having withdrawn from combat. Reloading of these huge shells was carried out by means of a roof-mounted (temporary) crane which was erected on the back of the cab and lowered shells through a removable hatch in the roof of the casemate and down onto the stowage racks.





Reloading process for the Sturmtiger was laborious but straightforward. 1) Unpacking the shell after rolling it into place on a pair of wooden rails. 2) Attaching the clamp for the crane to lift the shell. 3) Hoisting the shell up with crew to keep it steady. 4) Lowering the shell through the roof hatch to be racked inside. Source: Schneider.

Rebuilt for the Wehrmacht, the mortar was named the 38cm Rocket Launcher RW61 (RW – Raketenwerfer) and fired two types of shell, an explosive shell (Raketen Sprenggranate 4581) for general use, and a hollow-charge shell (Raketen Hollandungsgranat 4592) specifically for targeting reinforced concrete structures, as the warhead could penetrate up to 2.5 m of reinforced concrete. The range, however, was dependent on temperature ranging from a maximum range of 4,200m at -40 C to 5,900m at 50 C, and 6,650m at 15 C. This very large difference in shell performance was because it used a combustion process of propellant as the rocket was fired which was slower-burning in cold weather – the result were very lengthy range/temperature tables for the crew to use in order to accurately lay the gun. Not only was the range affected by temperature but so was shell flight and accuracy. To account for these discrepancies temperature measurement was important in the vehicle and the crew was provided with details range tables listing the elevation, range and temperature in order to maintain accuracy. The minimum range for firing from the tables was just 50 m.

Each shell came in two parts: a case about 550 mm long holding 40.1 kg of diglycol powder (rod form) as the propellant, and the H.E. shell itself carrying 122.5 kg of Amatol 50/50 high-explosive (with six P.E.T.N. pellets acting as the exploders), forming a complete 1,449 mm long (1,440 mm shell and case plus 49 mm fuze) long. Each shell used the same Treibnatz 4581 rocket motor and each case was thin-walled with 32 venturi holes in the bottom to vent out the propellant gases. The venturi holes were angled at 14 degrees to the axis of the rocket, and together with the splines which went into the rifling of the gun caused the shell to rotate clockwise in flight for stability.

Following examination of the records at the Sommerda factories in 1945, it was determined that there were two types of fuzes produced for the Sturmtiger shells. The first was the A.Z.KM 8m.r. (or K.N.9) direct action and delay fuze (percussion fuze with an optional delay of 0.12 seconds) for the High Explosive Shell (4581), and the A.Z.KM.10 hollow charge fuze (nose percussion with no delay) for the hollow charge shell (4592). The delay fuse was found to sometimes malfunction when striking a target at an angle of less than 14 degrees requiring multiple impacts before it would function. When striking a hard target at a steep angle, therefore, the round could actually break up without detonating so the delay on the fuze was not used when firing against hard targets or when the ground was very hard.



38cm Raketen-Sprenggranate 4581 (High Explosive) (left) and 38cm Raketen-Hohlladungsgranate 4592 (right). Source: War Office(UK) 1945 (left) and Navweaps (right)



The disassembled 38cm Raketen-Sprenggranate 4581 (High Explosive) shell with the HE containing section at the front. Source: US Army Catalog of Enemy Ordnance

Elevation was by means of a crank at the left of the mounting and could elevate the gun between 0 and 85 degrees with a traverse-crank over the barrel controlling side-to-side movement. This traverse movement allowed firing up to 10 degrees each way.

The barrel was radically different in design to other guns, with a cast outer body and a liner inside made from steel about 12 mm thick. Into this liner were cut nine rifling grooves into which splines on the rocket would sit and then rotate during firing. During firing, the gases produced were vented through the gap between the inner barrel and the outer barrel sheath. The two pieces of the barrel were held together at the breech and muzzle with steel rings and by drilling 32 holes the gases from combustion could be vented forwards keeping the gas out of the crew space and reducing the recoil of the gun.



Dunkelgelb-camouflaged Sturmtiger used during the Warsaw Uprising.