Summer 1943 — a SIG 33, or Sturminfanteriegeschütz 33, advancing with the 23rd Panzer Division through the Russian countryside, source: worldwarphotos.info, with permission of the operator, edited

Origins of the Vehicle

During the fighting in Stalingrad, German units faced many problems specific to urban warfare. One of them was the need to dislodge defenders who had fortified themselves inside large multi-storey buildings. Driving them out in room-to-room fighting was a slow process that 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 a factory hall with thick walls. 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 building without destroying everything around it. Air power was of course also an option — a dive bomber could strike a designated house with reasonable precision, but this was a costly and time-consuming solution, and attacking at low altitude over a city carried 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. Their requirement was conveyed to the Army High Command at Hitler's conference on 20 September 1942. The new fighting vehicle did not need to be fast — firepower and robust armour were what mattered. The German High Command reacted with remarkable speed. The Berlin firm Alkett (Altmärkische Kettenwerk) was immediately tasked with designing and developing not one but two new armoured vehicles suitable for this role.

The first of these was to prioritise speed above all else — thoroughness and refinement of design were secondary considerations. Only the second vehicle, which did not need to be available as quickly, was to be the fully developed and standard type for mass production. That second, more sophisticated vehicle later became the Sturmpanzer IV, also known as the Brummbär. In this article, however, we will say more about the first of the two armoured vehicles developed to destroy urban buildings — a vehicle that served only as a kind of stopgap solution, of which just 24 examples were built, and which bore the designation Sturminfanteriegeschütz 33.

Probably one of the twelve Sturminfanteriegeschütz 33 that managed to reach Stalingrad before the encirclement, source: worldwarphotos.info, with permission of the operator, edited

The task handed to Alkett was not an easy one. Delivery of the first minimum 6 — and ideally 12 — examples of the new armoured vehicle was required within a mere 14 days! Alkett's engineers had no time for lengthy deliberation. The new vehicle had no choice but to be assembled from as many already-existing components as possible, with the minimum of new elements.

Choice of Weapon

Choosing a suitable weapon was relatively straightforward. The obvious choice was the heavy infantry gun sIG 33 (sometimes written s.I.G. 33) in 150 mm calibre — or rather its modified variant sIG 33/1 (developed by Škoda Plzeň specifically for installation in armoured vehicles).

The sIG 33 (schwere Infanterie Geschütz — heavy infantry gun) was a robust and reliable weapon of great destructive power, available in comparatively large numbers. Its principal weakness was its limited range. The gun had been developed in the early 1930s based on lessons from the First World War, and its intended role was close-range fire support for infantry. Given the typical pace of infantry advance in the First World War, a maximum range of 4.7 km had originally seemed adequate. For the tempo of Blitzkrieg warfare, however, it was no longer sufficient. If artillerymen wanted to keep pace with a rapidly advancing front line, they had to change position frequently — which meant limbering up the gun each time (behind a half-tracked prime mover or a six-horse team), moving, unlimbering, and preparing to fire again. Because of this, the sIG 33 rarely played a significant role in the attack.

Sturminfanteriegeschütz 33, summer 1943, source: Flickr.com, with permission of the publishing user, edited

For the new armoured vehicle being requested, the gun's short range was no drawback whatsoever. In this role the gun was to fire at buildings in the middle of an urban area — from a distance of hundreds rather than thousands of metres, and often from just a few dozen metres across a square or a street. And in terms of destructive power, the sIG 33 fully met the soldiers' requirements. Its standard shell, the Jgr. 38, weighed 38 kg, of which a full 8.3 kg was explosive filling. The other component needed for the new vehicle was a chassis and hull, and these were taken from the assault gun StuG III (which, incidentally, was also being series-produced at Alkett). Virtually the only genuinely new element was the armoured fighting compartment, which was designed as simply as possible — a plain rectangular box, fixed rigidly (i.e. non-rotating) to the hull. The design and drawings for the new vehicle were completed within just two days of the assignment being given. Alkett's workers then delivered their own remarkable feat: the first twelve new vehicles were completed by 13 October 1942 — less than a month after the conference at which the plan to build such a vehicle had been conceived! A further twelve were delivered in November, and with that production definitively ended.

During development the new vehicle was referred to under various designations, including Sturmgeschütz mit sIG and sIG 33 auf Fahrgestell PzKpfw III (Sfl.). It ultimately received the official designation Sturminfanteriegeschütz 33 — literally "assault infantry gun."

Choice of Chassis

As its basis, older used chassis from StuG III assault guns of various variants (from Ausf. B through Ausf. E) were used — vehicles returning to Alkett from the front for major overhaul. The standard StuG III had a hull front plate 50 mm thick, which was considered insufficient for the new vehicle. An additional 30 mm armour plate was therefore bolted to the front of the Sturminfanteriegeschütz 33's hull.

Sturminfanteriegeschütz 33, source: Flickr.com, with permission of the publishing user, edited

Vehicle Description

The running gear consisted on each side of six road wheels sprung by torsion bars. The wheels were 520 mm in diameter and fitted with rubber tyres for a smoother ride. They were double wheels with the track guide teeth running between the two discs. The first and last road wheel on each side had an additional damper (as these wheels were subjected to the greatest stress during travel). At the front was the toothed drive sprocket and at the rear the idler wheel. The upper run of the track was supported by three 310 mm diameter return rollers. The tracks were 380 mm wide.

In place of the original low fighting compartment of the StuG III, a significantly larger compartment was fitted, welded from flat armour plates. The compartment was wide enough to extend over the track guards on both sides. These, however, were too thin to provide a solid floor for the compartment, so they were reinforced with additional 15 mm plates. On the left side, a section of the original StuG III front wall was retained, containing the driver's vision port. The front wall of the new fighting compartment adjoined this section — with a corresponding cutout at that point. Slightly to the right of centre, the barrel of the sIG 33 passed through the front wall. Connected to the barrel was a separate armour plate, mounted in guide rails on either side. This plate moved up and down together with the gun barrel during aiming. Below the barrel there was a further small movable armour plate. When the barrel was horizontal or only slightly elevated, this plate lay folded down beneath it. When the barrel was raised to a greater angle, this plate also rose, closing the open space beneath the gun barrel. The design of the front wall allowed horizontal traverse of a mere 3 degrees to each side. Vertical elevation ranged from -3° to +25°. To the left of the gun in the front wall was an MG 34 machine gun embrasure, taken from the PzKpfw III tank.

In the right side wall of the fighting compartment there was a small opening for emergency use by the crew's personal weapons, sealed by a metal plug. The rear wall had two crew entry hatches, and there was a further hatch in the roof plate. The roof also had an oval opening through which the gun's periscopic sight extended, protected by a raised sheet-metal hood. Beside it, a circular opening was cut for the installation of a ventilator fan — though as far as is known, fans were never actually fitted and the circular opening was simply welded shut again. The front wall of the fighting compartment was 80 mm thick and angled at 9 degrees. The side walls were 50 mm thick at 15 degrees, and the rear wall was 30 mm thick (15 mm is also sometimes cited). The roof was 20 mm thick (10 mm is also sometimes cited).

Sturminfanteriegeschütz 33 captured by the Soviets, source: Wikimedia, Public domain, edited

Behind the fighting compartment came the engine compartment, housing the twelve-cylinder Maybach HL 120 TRM petrol engine with a displacement of 11.9 litres, producing a maximum of 300 horsepower at 3,000 rpm. A driveshaft ran from the engine to the gearbox at the front of the hull. The gearbox was the Zahnradfabrik SSG 77 type with six forward gears and one reverse. Fuel capacity was 310 litres. The Sturminfanteriegeschütz 33 weighed approximately 21 tonnes and could achieve a top speed of around 40 km/h. Only 30 rounds of gun ammunition could be stowed on board — though given the vehicle's purpose, this was not a serious handicap. 600 rounds of MG 34 machine gun ammunition were carried. The crew consisted of five men: driver, commander, gunner and two gun loaders. A Fu 5 radio set was installed. Photographs confirm that some vehicles were fitted with wide winter tracks.

Combat Deployment

The first twelve Sturminfanteriegeschütz 33 produced were dispatched east immediately. At the end of October 1942 they arrived in the area of the River Chir, approximately a hundred kilometres west of Stalingrad. The vehicles were split equally between two assault gun battalions: Sturmgeschütz-Abteilung 177 and Sturmgeschütz-Abteilung 244. Both battalions received orders to deploy these vehicles in Stalingrad without delay, which they did. At the beginning of November 1942, six of the vehicles took part in Operation Hubertus — an attempt to destroy the last positions of the Soviet 62nd Army in the northern part of the city on the west bank of the Volga. The Sturminfanteriegeschütz 33 also fought in other parts of the city, including the centre itself. Details are essentially unavailable, but all 12 vehicles were lost in Stalingrad along with the rest of the encircled forces.

When the next twelve vehicles — built in November 1942 — arrived at the front, Stalingrad was already encircled, so these vehicles could no longer enter the city. They were instead committed to the attempt to break the encirclement from outside, as part of the specially formed Sturminfanteriegeschütz Lehr Bataillon XVII, fighting alongside the 22nd Panzer Division. The attempt to break through the pocket failed. In the weeks and months that followed, the Sturminfanteriegeschütz 33 fought in the retreating battles on the southern sector of the Russian front. On 11 April 1943 the last seven surviving examples were all transferred to the 23rd Panzer Division. According to that division's records, the last vehicle of this type was lost in October 1943 (some authors suggest that these vehicles appeared in a report as late as September 1944, but this is highly unlikely).

A Sturminfanteriegeschütz 33 passing the wreck of a Soviet Katyusha rocket launcher, source: Flickr.com, with permission of the publishing user, edited

In November 1943 a report was compiled summarising operational experience with these vehicles. Among other findings, the report noted that the vehicle lacked adequate observation devices — a fair criticism, since beyond the driver's vision port there was only the gun's periscopic sight. Crews requested the installation of at least a binocular observation periscope. The horizontal traverse of the gun — three degrees to each side — was also deemed insufficient. The use of older, already-worn-out chassis was viewed critically: the accumulated wear manifested itself in frequent failures of the engines, drivetrain, running gear and tracks. The destructive power of the main weapon, on the other hand, was assessed entirely positively.

Technical Data

ARTICLE
CONTENTS:

ORIGINS OF THE VEHICLE

CHOICE OF WEAPON

CHOICE OF CHASSIS

VEHICLE DESCRIPTION

COMBAT DEPLOYMENT

TECHNICAL DATA