3.7 cm Selbstfahrlafette L/70

 German Reich (1935)
Self-Propelled Anti-Tank Gun – 1 Prototype Built

It is well known that prior to WW2, the Germans were heavily involved in tank development. What is less known, is that they also experimented and evaluated anti-tank self-propelled vehicles, based on half-track chassis. These were intended to provide a quick anti-tank response to enemy armor formation attacks. This overall concept, while tested, was never fully developed and only a small number of prototypes were made, including the vehicle known as  3.7  cm Selbstfahrlafette L/70. While a single prototype was built, sadly, the general development of German pre-war self-propelled anti-tank half-track is poorly documented in the sources.

History

During the early 1930s, in the Germany Military circles, the concept of using fast anti-tank vehicles that could outrun tanks was beginning to take shape. For this reason, on 20th November 1934, a program to develop and build such a vehicle was initiated. The chassis for this new self-propelled anti-tank vehicle project was to be based on a half-track. The choice to use a half-track chassis was probably based on its good overall road and off-road driving performance. While it could not fully match a tank’s off-road performance, especially on poor terrain, it still would perform better than ordinary wheeled trucks.  The overall performance that this vehicle would be able to achieve was best described in the Wa Prw (short for Waffen Prüfungsamt, the automotive design office) report called ‘Offensive Defense Against Tanks’ (Offensive Abwehr von Panzerwagen) published at the end of October 1935.

In its introductory part, it described the earlier thinking that the only weapon that could successfully stop a tank was another tank. It followed on by elaborating that this was not the case anymore, providing examples that bombers were not employed against bombers, but instead this was the job of the smaller fighter aircraft. Another example was that smaller and more maneuverable ships could cause huge damage to much larger and expensive but slow warships. The key element in defeating these threats was superior speed and maneuverability. The armor came in second place, and only to a limited extent, not to hinder the performance of the overall mobility.

If these factors would also prove to be beneficial for an anti-tank vehicle was a good question. In order to test the new concept of an anti-tank vehicle, it should fulfill several criteria including high road speed; good overall cross-country speed, similar, or when possible, superior to that of tanks; small dimensions; accurate fire while stationary; effective firing range up to 700 meters; cheap; and if possible, use components that were already in production. The last request was a bit unusual but optional. The main gun was (if possible) able to be dismounted to be used as a towed gun

The two main problems in this report indicated for this vehicle were the creation of the chassis with enough mobility, and finding a sufficiently strong weapon to fit in it. In the case of the gun, it had to have the best possible armor penetration, but the recoil had to be manageable. Quite interestingly, this report also mentioned the possibility of alternatively using some kind of unspecified rocket launcher. The benefit of this weapon is no recoil and the armor-piercing round could be replaced with large high-explosive rockets.

Ultimately, only two trial vehicles were completed and submitted for testing during the period of 1935 and 1936. One of these was the 3.7 cm Panzerabwehr-Geschütz auf Selbstfahrlafette and the other one was simply described as Tankjager (during the early 1930s, the German Army used the term tank, later being fully replaced with Panzer).

3,7 cm Selbstfahrlafette L/70

For producing one such vehicle prototype, the Wa Prw issued a military contract to two firms, each designated to produce different necessary components. The company Hansa-Lloyd was tasked with building the chassis and the company Rheinmetall-Borsig for designing and building its main weapon and a turret. It was quite common practice in Germany, prior to the war, to include a number of different manufacturer companies in one project. The German industry at that time was still undeveloped and including other companies allowed them to gain valuable experience in armored vehicle design and construction.

When the vehicle was completed, it received an unusual but simple 3,7 cm Selbstfahrlafette (self-propelled) L/70 designation. Unfortunately due to being poorly documented in the sources, not much is generally known about this vehicle. What is known is that it was completed in 1935.

Specifications

The Chassis

The 3,7 cm Selbstfahrlafette L/70 chassis was based on the HL kl3(H) half-track vehicle, developed by Hansa-Lloyd. A pre-war attempt to design a cheap and easy-to-produce half-track. This vehicle chassis could be divided into three major compartments. The front driver compartment was fully protected except for the wheels. The central firing compartment housed the main weapon. And lastly, the rear positioned engine compartment.

The Engine and the Running Gear

The 3,7 cm Selbstfahrlafette L/70 was powered by a Borgward engine, providing 70 hp @ 2,600 rpm. The engine was positioned to the rear of the chassis, somewhat unusual for German half-track vehicles. The installed transmission had 4 speeds, with a 2-speed transfer case. The maximum speed on the road was an excellent 50 km/h. While the cross-country speed is not listed in the sources it was likely slightly slower.

The torsion bar suspension consisted of one front drive sprocket, 5 road wheels, and a rear idler, larger than the wheels. Each track was 1.6 meters long. Two steering wheels were located to the front of the vehicle. These, like all German half-track designs, were not powered.

Armored Body

On top of the chassis, a larger armored superstructure was placed. The overall armor thickness is unknown, but given the fact that it was intended to be a lightweight vehicle and easy to build, it would most likely provide protection against small-caliber bullets. The high angled armored superstructure slides also served to provide additional protection.

The front part of this armored superstructure where the driver was positioned, was provided with at least one hatch, which was placed on the right side. Sadly there is no photograph of the vehicle’s left side, but it’s highly possible that another door was also added to this side. For observing his surroundings, the driver was provided with three visor slits. The two front steering wheels were completely exposed and could be easily damaged by enemy fire. Whether this was intentional or hoped to be later covered in armored plates, given that this was only a prototype vehicle, is sadly unknown.

The center of the vehicle was provided with highly angled armor plates. These spread from the bottom towards the top. While this arrangement provided additional protection, it also provided the crew with somewhat more working space inside the vehicle. On the right side, possibly also on the left, a rectangular hatch was added, possibly to serve as an entering point for the crew but also for maintenance.

The engine compartment had three ventilation grill hatches. One to the rear that could be opened and two on each side. Interestingly, in one photograph, these side hatches were covered by an armored plate. These probably offered a large target for the enemy and were thus replaced with simple armored cover. In addition, there was another two-part hatch placed on the top of the engine compartment.

Turret

On top of the armored superstructure, an open-top turret was placed. Unlike a tank turret, the 3,7 cm Selbstfahrlafette L/70 turret was more like an extended armored shield of its main gun mount, somewhat similar to the later Sd. Kfz. 222 armored cars series. The front of the turret was occupied by the main gun positioned in the center. To the left of the gun was a hatch for the gun sight. A machine gun ball mount was placed on the opposite side. There were no side visor slits or hatches but given that the turret top was open, this was not needed. To the rear, a small hatch was added. It probably served to remove spent cartridges or was used for gun barrel removal. On top of the open turret, a round-shaped anti-aircraft machine gun mount was placed. The whole turret could rotate 360°.

Armament

The main armament consisted of one 3.7 cm PaK L/70 anti-tank gun especially developed by Rheinmetall. It had a horizontal slide breach and was probably semi-automatic. This weapon is somewhat an enigma as very little is known about it.  What is known is that when firing an armor-piercing round, which weighed some 0.710 kg, the muzzle velocity was 900 m/s.  To the rear of the breach, a canvas bag was located to serve to catch any spent cartridges. The elevation of this weapon was -7° to +20°. The main ammunition storage bin was located behind the gun. The unusual feature of this gun was the cone-shaped muzzle brake. To improve the stability of the gun, a larger metal bar with two round cutouts was added to the rear of the gun.

The secondary armament consisted of two MG 34 7.92 mm machine guns. One was placed in the turret machine gun ball mount. The second one was placed on top of the turret in a specially designed anti-aircraft mount. No information is provided in the sources about the precise amount of ammunition for the main and secondary weapons.

The Crew

The number of crewmen is not mentioned in the sources. Given the vehicle’s overall small size, we can give an educated guess that it would likely consist of at least three crew members. The driver was positioned in the front driver compartment. Behind the driver’s compartment, the fighting compartment with the main gun was placed. On a few surviving photographs of this vehicle’s interior, it can be seen that two crew members were needed to operate the gun. The gunner, who was likely also the commander of the vehicle, and the loader. The gunner was positioned to the left of the gun while the loader was on the opposite side. It also appears given that both machine guns were placed on the right vehicle side and would be operated by the loader. This was far from perfect, as these two would be overburdened with more tasks than they would be able to handle. A third crew member would have greatly improved the performance of the gun operating crew, but there appears no available space for one inside the cramped fighting compartment.

Fate

According to Rheinmetall-Borsig documentation, salvaged after the war and dated from 1940, only one 3,7 cm Selbstfahrlafette L/70 vehicle was ever built. It was supposedly tested extensively prior to the war. As mentioned earlier, due to the lack of sources, the precise fate or use of this vehicle is not well documented. But the fact that only one vehicle was built gives us an indication that the design was not good enough to warrant serial production. The fate of the prototype is unknown, but it was probably scrapped during the war.

Conclusion

The 3,7 cm Selbstfahrlafette L/70 was a quite unusual concept developed by the Germans during the mid-1930s. It generally fulfilled a few aims of the German Army mostly regarding speed and firepower. The half-track chassis could achieve speed up to 50 km/h on roads, while the longer 3.7 cm gun likely had much better armor-piercing performance than the 3.7 cm Pak 36 that was in service at that time. The negative sides were the generally small and cramped interior, low armor thickness, use of a gun that was not in service, and that the half-track was generally not cheap for production. But the reasons why this project was rejected are sadly not available. Due to almost nonexistent sources on this unusual vehicle, we will never know its overall performance nor its reason for rejection.

Dimensions (l-w-h)	5.1 x 2 x 1.65 m
Total weight	6 tonnes
Crew	3 (Commander/Gunner, Driver and Loader)
Propulsion	Borgward  70 hp @ 2,600 rpm
Speed	50 km/h,
Armor	Unknown but probably light
Armament	3,7 cm PaK L/70

 

Sources

• P. Chamberlain and H. Doyle (1978) Encyclopedia of German Tanks of World War Two – Revised Edition, Arms and Armor press.
• D. Doyle (2005). German military Vehicles, Krause Publications.
• T.L. Jentz and H.L. Doyle (2005)  Panzer Tracts No.7-1 Panzerjager

• Walter J. Spielberger (1993), Fahrzeuge Des Deutschen Heeres 1909-1945, Motorbuch Verlag
• https://www.armedconflicts.com/3-7-cm-Selbstfahrlafette-L-70-t34932