3.7 cm Flak 43/1 anti-aircraft cannon on the schwerer Wehrmachtschlepper tractor chassis; source: www.pietvanhees.nl, used with permission of the operator, edited

A New Generation of Half-tracks

Germany entered the Second World War equipped with six standard types of half-track artillery tractors, with towing capacities ranging from just 1 tonne (Sd.Kfz. 10) to 18 tonnes (Sd.Kfz. 9). Although these six types differed enormously in power and weight, they shared a number of characteristics. First: all of them had grown out of the development programme launched in the early 1930s, meaning their designs were hardly cutting-edge by the time war broke out. Second: although intended for off-road use, all of these vehicles had been designed to also manage fast travel on paved roads — hence their relatively narrow tracks with rubber pads to dampen vibration at road speeds. They were essentially engineering compromises between road speed and cross-country mobility. Third: all existing types had been conceived primarily as tractors. Their job was to tow loads behind them, not carry them on a platform — which is why most variants had rows of seats for soldiers rather than a cargo bed. And fourth: each of the six vehicles had been developed and manufactured by a different company, meaning any notion of mutual standardisation was entirely out of the question.

Towards the end of the 1930s the Army therefore began exploring the possibility of developing a new generation of half-tracks that would bring not only more modern engineering but also greater manufacturing and operational efficiency. This programme, however, never gained any significant priority and ultimately came to nothing. Hitler himself was reportedly convinced that the existing tractor types were perfectly adequate for the coming war, and he preferred to concentrate development and production capacity on combat vehicles. And it must be said that the successes of the German Army in the lightning campaigns of 1939 and 1940 appeared to prove the Führer right.

The German invasion of the Soviet Union changed everything. In late 1941, German forces experienced their first Russian autumn — the infamous mud season — followed shortly afterwards by their first Russian winter. More importantly, they experienced their first strategic failure. The enemy could not be beaten in another lightning campaign, and losses in men and equipment were enormous. The Germans realised that the war in the East would not be over in a matter of months, and that the Russian front would demand vast quantities of all kinds of equipment, including half-track vehicles. There was now a genuine need to find efficiencies that would allow half-tracks to be produced more cheaply, while also adapting their design more closely to the specific demands of the Eastern Front.

schwerer Wehrmachtschlepper with anti-aircraft gun superstructure (mit Flak-Aufbau) and auxiliary armour (mit Behelfspanzerung); source: Worldwarphotos.info, used with permission of the operator, edited

In May 1942 the Germans therefore launched a programme to develop what was effectively a third generation of half-tracks. In the interests of standardisation and manufacturing efficiency, this new generation was to consist of just two types: a light one (leichter Wehrmachtschlepper) and a heavy one (schwerer Wehrmachtschlepper, abbreviated sWS). Development of the former was entrusted to Adlerwerke of Frankfurt, while the latter was to be prepared by Büssing-NAG — specifically its factory in the Berlin district of Oberschöneweide.

Technical Description

Büssing-NAG had all the necessary experience, as it was already producing the Sd.Kfz. 6 half-track tractor at the time. In May 1942, company representatives signed a contract with the Waffenamt for the development of the new vehicle and the construction of five evaluation prototypes. Just two months later, on 27 July 1942, it was decided that Büssing-NAG would discontinue production of the existing Sd.Kfz. 6 in order to concentrate fully on the new schwerer Wehrmachtschlepper. The new vehicle was designed from the outset to suit the requirements of the Eastern Front. What use was the ability to travel quickly on paved roads when such roads were the exception rather than the rule in Russia? Speed was no longer the priority — what mattered was the ability to push through terrain, mud and snow. In addition to towing artillery, the new half-track was to be used far more extensively for supplying frontline units. In its basic configuration it was therefore to have not rows of seats but a cargo bed, much like an ordinary truck.

Büssing-NAG kept to the Army's requirements, and the resulting design genuinely adhered to two fundamental principles: simplicity and durability. The front wheels supported the engine section and assisted with steering. Behind them ran a fairly long track unit, consisting of a toothed drive sprocket at the front, a spoked idler wheel at the rear, and five road wheels 800 mm in diameter. Each road wheel was made up of two discs with lightening holes and a rubber tyre to dampen vibration (note: a differently designed wheel was used on some later vehicles). The discs of the even- and odd-numbered wheels were spaced and oriented differently on their axles — with the direction of their dish also reversed — allowing the wheels to overlap one another in the standard interleaved arrangement that the Germans applied to most of their half-tracks and later tank types as well.

3.7 cm Flak 43/1 anti-aircraft cannon on the schwerer Wehrmachtschlepper tractor chassis; source: www.pietvanhees.nl, used with permission of the operator, edited

The road wheels were sprung by torsion bars, which by their nature introduce a technical challenge: if the wheels on both sides of the chassis were positioned directly opposite one another, their torsion bars would meet in the middle — clearly impossible. On older half-tracks such as the Sd.Kfz. 6 already mentioned, this problem was solved by offsetting the wheels on one side of the chassis slightly further rearward, so that the road wheels on the left and right sides were not directly opposite one another.

On the new schwerer Wehrmacht­schlepper, however, the designers used a different solution. The swing arms on which the road wheels were mounted were oriented in opposite directions on each side of the chassis. On the right side, the arms pointed rearward, so each road wheel was effectively positioned behind its torsion bar. On the left side, the arms pointed forward, so each wheel sat ahead of its torsion bar. This meant the wheels on both sides could be placed directly opposite one another while their torsion bars, running transversely across the chassis frame, never intersected. Each track was 500 mm wide and consisted of 55 links, though each link itself was made up of two parts: a main section with a grouser and a pair of inner guide horns, and a simpler connecting piece (note: tracks of a different design were used on some later vehicles).

The vehicle's chassis was of ladder-frame construction. At the front was the engine compartment, housing a Maybach HL 42 TRKMS petrol six-cylinder engine with a displacement of 4.198 litres, developing a maximum of 100 hp at 2,800 rpm. Even at first glance it is obvious that the vehicle was hardly overflowing with power. For comparison, consider its parameters alongside those of the older Sd.Kfz. 6. The Sd.Kfz. 6 had an unladen weight of 7.5 tonnes and a 115 hp engine, enabling a top speed of around 50 km/h on roads. The unladen schwerer Wehrmacht­schlepper weighed two tonnes more and had 15 fewer horsepower under its bonnet — so it is no surprise that its top speed was a mere 27 km/h. But as noted above, speed was not the priority in designing the new vehicle. What mattered was making it through snow and mud and delivering as much supplies as possible to the fighting units. And those requirements it met. The wide tracks distributed the vehicle's weight effectively, preventing it from bogging down even in soft ground. Towing capacity was a solid 8 tonnes, and an impressive 4 tonnes of cargo could be carried directly on the platform — considerably more than on the older tractor types.

3.7 cm Flak 43/1 anti-aircraft cannon on the schwerer Wehrmachtschlepper tractor chassis; source: www.pietvanhees.nl, used with permission of the operator, edited

The radiator and a large fan were positioned ahead of the engine itself. Behind the engine was the main Zahnradfabrik Typ Kb 40 D gearbox with four forward speeds and one reverse, connected via a short shaft to a two-speed reduction gearbox. From there drive was transmitted to the track unit's drive sprockets via a set of steering and service brakes. The steering brakes handled turning: the front axle alone was only sufficient for very gradual curves. Once the driver turned the steering wheel more than 5° (this figure is given without guarantee), the steering brake for the relevant track drive sprocket engaged automatically, slowing the track on the inside of the turn and causing the vehicle to corner more sharply. The steering brakes were actuated by a pneumatic system using compressed air stored in two pressure tanks mounted inside the ladder-frame chassis.

The fuel tank, with a capacity of 240 litres, was located at the very rear of the chassis frame, with the filler cap on the rear panel. On this fuel supply the half-track could cover approximately 300 km on roads and around 150 km in moderately difficult terrain. A winch with a steel cable could optionally be fitted inside the chassis frame, though it was not standard equipment. Where fitted, the winch had a pulling capacity of 5 tonnes and was driven by a shaft from the reduction gearbox.

The basic production version of the half-track was the cargo variant with a flat bed and folding wooden plank sides — the so-called Pritschen-Aufbau. A tall wooden bulkhead separated the cargo bed from the driver's cab. A canvas roof fitted over a frame above the cargo area provided protection from the elements, and the same canvas could be stretched over the open driver's cab — which, apart from a windscreen and the rear wooden bulkhead, was otherwise unenclosed.

3.7 cm Flak 43/1 on the schwerer Wehrmacht­schlepper tractor chassis; note the folded-down side panels and the prepared eight-round 37 mm magazines; source: www.pietvanhees.nl, used with permission of the operator, edited

Anti-aircraft Gun Carrier

Of far greater interest to us, however, are the combat variants of the schwerer Wehrmacht­schlepper rather than the cargo version. Specifically, we will look at two official and two unofficial combat variants of this half-track. The first of the official ones was the carrier for the 37 mm Flak 43/1 anti-aircraft cannon. Instead of a wooden cargo bed, this version received an open fighting compartment with a metal floor and perforated side panels that could be folded down and locked horizontally to extend the floor area around the weapon. A closed ammunition box was built into the rear. The engine compartment and driver's cab received new "armour" — though the inverted commas are entirely warranted, since cost-saving measures meant that softer-grade steel plate was used. At 15 or 16 mm on the front faces, 12 mm on the sides and 8 mm on the roof, this was probably not even enough to stop a 7.92 mm armour-piercing rifle bullet. Against ordinary small-arms ammunition and small shell splinters from nearby explosions, however, it probably sufficed. Indeed, even the vehicle's official designation referred to this protection merely as "auxiliary" armour: 3,7 cm Flak 43/1 auf Selbstfahrlafette schwerer Wehrmacht­schlepper mit Behelfspanzerung.

The engine grille armour retained an opening for the starting crank, and the engine bonnet had two access hatches for servicing the powerplant. The driver and his co-driver had vision ports in the front and side panels. The armoured cab was open at the rear, so both men entered their seats from the fighting compartment. The co-driver, who also served as vehicle commander, additionally had a roof hatch directly above his position. The armoured half-track without its weapon weighed approximately 10.5 tonnes — about one tonne more than the standard cargo version. Some sources state that the vehicle's weight with the cannon, ammunition and crew reached 15 tonnes, though this seems somewhat exaggerated. Such a figure would significantly exceed the maximum limit for the fully laden cargo version (13.5 tonnes) and would presumably have caused a noticeable deterioration in handling and overloaded the chassis. Other sources give a figure of "only" 14.1 tonnes.

schwerer Wehrmacht­schlepper with Flak 43/1 cannon at a German vehicle dump, with a field conversion of a standard cargo sWS fitted with the same weapon standing beside it; source: flickr.com, Public Domain, edited

The 3.7 cm Flak 43/1 Cannon

The Flak 43/1 was a modified version of the towed Flak 43 cannon, an anti-aircraft weapon developed by Rheinmetall-Borsig. The mounting allowed full 360-degree traverse and vertical elevation from -7° to +90° (sometimes cited as -10° to +90°), making it clear the weapon could also be used against ground targets. The cannon operated in automatic mode, using propellant gases tapped from the barrel to drive the loading mechanism. Rounds were assembled into eight-round magazines and fed into the weapon from the left along a horizontal feed tray. The loading mechanism was deliberately positioned at the gun's centre of gravity, so the changing weight of the ammunition as firing and loading proceeded had no effect on aiming accuracy. The gunner and his assistant sat on seats attached to the right side of the mounting pedestal, with an ejection port for empty cases directly behind them.

The standard Flak 43 weighed 1,248 kg, and its modified variant the Flak 43/1 likely differed little in this respect. Maximum theoretical rate of fire was 250 rounds per minute, with a practical rate of around 180 rounds per minute. The standard ammunition was the high-explosive incendiary tracer round designated 3,7 cm Strenggranate Patrone Leuchtspur 18 (abbreviated 3,7 cm Sprgr Patr L'spur 18). The complete round weighed 1,500 grams, with the projectile itself weighing 635 grams, of which 24 grams was the explosive charge. This round left the barrel at 820 m/s and could reach a maximum altitude of 4,800 metres, though the effective engagement ceiling was 4,200 metres. Against ground targets the maximum range was around 6,585 metres. Other ammunition types were available, of which we will mention only the armour-piercing 3,7 cm Panzergranate Patrone 18, weighing 1,540 grams in total with a 680-gram projectile.

Series Production

Following approval of the new vehicle design, the Waffenamt signed two large contracts with Büssing-NAG. The first, concluded in 1942, covered the delivery of exactly one thousand half-tracks — 625 in the cargo version (mit Pritschen-Aufbau) and 375 in the anti-aircraft gun carrier version (mit Flak-Aufbau). The second contract, signed in 1943, called for a further 2,300 vehicles, of which 1,725 were to be cargo versions and 575 anti-aircraft gun carriers.

another view of the field-converted standard cargo schwerer Wehrmacht­schlepper without armoured cab, fitted with the Flak 43/1 cannon; source: flickr.com, Public Domain, edited

The production plan called for the first 52 vehicles to be delivered in October 1943, a target that proved impossible to meet. In reality, the first five series-production schwerer Wehrmacht­schleppers were not completed until December 1943 — four in the cargo version and one mit Flak-Aufbau. In January 1944 five more vehicles left the Büssing-NAG factory in Berlin-Oberschöneweide, followed by seven in February, with output then slowly climbing to a peak of 92 vehicles in October 1944. Over the whole of 1944, the Berlin plant completed 559 cargo and 75 combat half-tracks. Production continued into 1945 despite mounting difficulties: in January and February of that year Büssing-NAG demonstrably completed 71 vehicles, after which detailed records are no longer available.

In 1943 the Waffenamt approached Ringhoffer-Tatra Werke AG in the Protectorate of Bohemia and Moravia, requesting that one of the company's factories also join the production of the schwerer Wehrmacht­schlepper. The Kolín railway carriage works — formally known as Továrna na vozy, a.s., Kolín — was selected for this purpose. The factory had already been redirected to war production by that point and was no longer building railway wagons or trams. In December 1943 it received an order for 500 cargo-version half-tracks. Preparations for production took many months, however, and the first seven complete vehicles did not leave the Kolín factory until May 1944. By the end of that year, a total of 90 cargo half-tracks had been built there. Seven more were completed in January and February 1945, and again records beyond that point are lacking. In total, at least 837 examples of the schwerer Wehrmacht­schlepper were probably built, of which at least 81 were in the anti-aircraft gun carrier configuration. In addition to the two final assembly plants described, a wide range of subcontractors naturally contributed to Wehrmacht­schlepper production.

Organisation

Given their low speed, schwerer Wehrmacht­schleppers armed with the Flak 43/1 were not assigned to armoured or other fast-moving formations, as they simply could not keep pace with them. They were most likely assigned to independent Army anti-aircraft units, within which they provided air defence primarily for infantry formations.

Panzerwerfer 42 150 mm rocket launcher on a schwerer Wehrmacht­schlepper chassis; source: flickr.com, used with permission of the publishing user, edited

Unofficial Conversions

The remaining three armed variants of the schwerer Wehrmacht­schlepper promised in our introduction can be dealt with more briefly. Alongside the official anti-aircraft vehicle already described, two unofficial field conversions of the same type also existed. The first actually carried the same weapon — the 3.7 cm Flak 43/1 — but was not a factory vehicle. Instead it was a field conversion based on the unarmoured cargo half-track with its standard wooden cargo bed (Pritschen-Aufbau). No detailed information about this modification is available, but several photographs of such a vehicle at a dump of abandoned German equipment at the very end of the war have survived. A handful of very poor-quality photographs also prove the existence of an armoured sWS fitted with the four-barrelled 20 mm Flakvierling 38 system. This was most likely also a field conversion — essentially a substitution for the Flak 43/1 cannon.

Self-propelled Rocket Launcher

The last variant to mention is one that was produced officially, but almost certainly in very limited numbers — possibly in a single evaluation prototype only. This was a self-propelled ten-barrel 150 mm rocket launcher. According to T. L. Jentz, the Waffenamt commissioned development of this vehicle from a firm called Martiini-Hütte of Salzkotten in North Rhine-Westphalia, in August 1944. No company of this name can be found online, however, so this information is offered without guarantee.

The armoured version of the Wehrmacht­schlepper served as the basis for this vehicle, with the armour extended to cover the rear half of the body as well. The result was a fully enclosed hull with large access doors in the rear wall and storage compartments on the sides. On the roof was a rotating mounting for the ten-barrel rocket launcher — the same weapon fitted to Opel Maultier half-tracks under the designation Panzerwerfer 42. The launch barrels themselves were taken from the standard towed 15 cm Nebelwerfer 41 rocket launcher and arranged in two rows of five. The rockets — 15 cm Wurfgranate 41 — were loaded from the rear into the barrels; they were available either as high-explosive (Spreng), weighing 31.8 kg, or smoke (Nebel), weighing 35.9 kg.

another view of the wrecked schwerer Wehrmacht­schlepper with ten-barrel rocket launcher; source: flickr.com, used with permission of the publishing user, edited

The rockets had an interesting design. The nose section housed a ballistic cap and impact fuze; the middle section contained the solid rocket propellant; and the warhead — filled with either explosive or smoke compound — was positioned somewhat unusually at the tail. Around the circumference of the rocket, just forward of the warhead, were 26 small nozzles angled at approximately 14° rather than pointing straight rearward. This angled arrangement imparted a spin to the rocket, which was essential for stable flight. The reason for placing the warhead at the tail was straightforward: when the rocket struck the ground nose-first, the warhead was still positioned relatively high above the surface, greatly increasing the blast effect of the explosion. The trade-off was that the rockets were complex to manufacture — some sources claim that a single rocket cost more than an entire Nebelwerfer 41 launcher.

The vehicle's interior was used for storing the rocket supply. Loading was probably carried out through a hatch in the roof of the body immediately behind the launcher mounting. Aiming was performed using the R.A. 38 sight (Richtaufsatz 38). Precise aiming was, however, a relative concept: the dispersion of rocket impacts was measured in tens of metres in width and hundreds of metres in range. This was not a weapon designed to destroy point targets, but rather larger concentrations of infantry or military equipment. The rockets were fired electrically, one after another in rapid succession, leaving the launch barrels at approximately 342 m/s with a very distinctive sound — Allied soldiers famously nicknamed the Nebelwerfer 41 the "screaming mimi." Maximum range was approximately 6,900 metres.

Technical Specifications

ARTICLE
CONTENTS:

A NEW GENERATION

TECHNICAL DESCRIPTION

ANTI-AIRCRAFT GUN CARRIER

THE FLAK 43/1 CANNON

SERIES PRODUCTION

ORGANISATION

UNOFFICIAL CONVERSIONS

SELF-PROPELLED ROCKET LAUNCHER

TECHNICAL SPECIFICATIONS