Nazi germany Nazi Germany (1944)
Prototype – 1 built

In 1943, an alternative drive system for the Panzer IV entered development. This was the Hydrostatischem Antrieb or Hydrostatic Drive, also known as the “Thoma” drive.

It was designed and produced in the Augsburg plant of ZF Friedrichshafe, and was tested on a turret-less Panzer IV Ausf. G chassis that had been badly damaged during combat operations.


Pz IV Hydro 2
Surviving Panzerkampfwagen IV mit Hydrostatischen Antrieb in the US. Note the now sloped engine deck, and the smaller rear drive wheels. (Source:-

The Thoma system operates in a similar way to the petrol/electric drive system produced by Porsche for his Tiger I concept vehicle that would later become the Ferdinand/Elefant. This system was a lot safer, however, as it was a petrol/hydraulic system. This gave the benefits of the Porsche system without the fire risk that plagued it so badly.

The Hydrostatic Drive system outside of the vehicle. Photo: – Spielberger Publishing

The Panzer IV chassis underwent heavy modification to be able to mount this new drive system. The engine compartment of the tank was almost completely removed and rebuilt. The drive was placed in the rear of the tank under a large sloping engine deck. Two oil pumps were installed behind, and connected directly to the normal Maybach HL 120 TRM engine. These powered two hydraulic motors. A swash plate drive sent the power through a reduction gear into the newly added rear drive wheels, which replaced the traditional idler wheel.

The new controls added to the Panzer, note the new control “wheel” and the many new dials. Photo: – Spielberger Publishing

Inside the crew compartment, the old drive shafts were removed along with the large gearbox and final drive assembly at the bow end of the vehicle. The traditional steering tillers were replaced with a crescent-like wheel, similar to the one found on Tiger I. Directional movement was achieved by two control cylinders. These cylinders regulated the volume of the oil inside the pump. This governed the amount of power the drive wheels would receive. Two large 780mm adjustable toothed idlers replaced the original Panzer IV drive sprockets.

Later in 1944, the vehicle was tested with a hydraulically powered turret. Unfortunately, more information on this modification is unavailable.

Tanks Encyclopedia’s own rendition of the Panzer IV with Hydrostatic Drive, by Jarosław Janas.


Only one prototype of the vehicle with this drive system was built by the time the Allies were knocking on Germany’s door. In April 1945, the US 3rd Infantry Division was advancing through southern Germany and into Bavaria. They broke into Augsburg on the 27th and had the whole city secured by the 28th. With the city, they captured the Zahnradfabrik plant, and the test vehicle.

The Turretless hull of the Panzer in the Zahnradfabrik plant. Photo: – Spielberger Publishing

After the war, the vehicle was shipped back to the United States, where it was subjected to thorough tests by Vickers Inc. Detroit, Michigan until at least 12th April 1946, when a report stating how the drive worked was drafted:

“The powertrain consisted of two staggered-plate oils pumps that are assembled as a unit and are driven by a 12-cylinder Maybach engine. Oil is pushed by the pumps to two separate oils engines which power the drive wheels of the tracks. The oil engines are attached to the final drive housings. The engine and power aggregate are located in the rear of the vehicle, and the vehicle is moved by rear mounted drive wheels. The volume of the pumps is controlled by the driver, who thereby controls the torque of the various pressure conditions that are created by the steering and stopping of the vehicle. In the same manner, the forward and backward movement of the vehicle is achieved by directing oil flow. Pressurized oil to activate the pumps and engines and for the high-pressure connections was advanced by a geared-wheel pump that was connected to the vehicle’s engine by direct drive.”

Unfortunately, the German test data has been lost to history. The vehicle was left in the open, exposed to the elements, at the U.S Army Ordnance Proving Grounds, Aberdeen in Maryland. In 2015 it was moved to the U.S. Army Center for Military History Storage Facility, Anniston, AL, USA, where it has the officially long-winded designation of “Tank, Medium, Full Track, Experimental Transmission, German Army, Steel, Tan, PzKpfw IV, 75mm Gun, German, 1945, World War II”.

Pz.Kpfw IV mit hydrostatischen antrieb
This Pz.Kpfw IV mit hydrostatischen antrieb is now in storage in the U.S. Army Center for Military History Storage Facility, Anniston, AL, USA. (Photo – Masa Narita)

An article by Mark Nash

Panzer IV mit Hydrostatischem Antrieb

Dimensions5.41 x 2.88 x 2.68 m (17.7×9.4×8.8 ft)
Total weight, battle ready25 tons
ArmamentRheinmetall 75 mm (2.95 in) KwK 40
2-3 MG 34/MG 42 7.92 mm (0.31 in) machine-guns
ArmorFrom 15 to 65 mm (0.59-2.56 in)
PropulsionMaybach V12 gasoline HL 120 TRM
(220 kW) 300 bhp@2500 rpm
SuspensionLeaf springs
Speed on /off road42 km/h (26 mph)
Total production1

Links & Resources

Panzer-IV und seine Varianten (Panzer IV and its Variants) Spielberger and Doyle.
Panzer Tracts No. 4, Panzerkampfwagen IV, Grosstraktor to Panzerbefehlswagen IV
Panzer Tracts No. 4-3, Panzerkampfwagen IV Ausf. H and Ausf. J, 1943 to 1945

Germans Tanks of ww2
Germans Tanks of ww2

Raupenschlepper Ost Artillery SPG
10.5cm leFH 18/6 auf Waffenträger IVb
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7 Responses to Panzer IV mit Hydrostatischem Antrieb

  1. Anne says:

    Very interesting.

  2. will5stars says:

    Was there any advantage to the Hydrostat transmission? It seems like a waste of resources to work on such an untested transmission type when the same engineers could be working on better improvements to other tanks.

    Great article as always!

    • MarkNash says:

      It granted slightly better acceleration and allowed the vehicle to be slightly more maneuverable. Very little was gained from the concept from the time spent on it. If a was developed further, it may have been a different story.

      – TE Moderator

    • Blockio says:

      If I’m not completely mistaken, it was partially designed by Ferdinand Porsche (don’t quote me on that), and we all know that he had a nag for designs that were innovative, but of questionable effectiveness *cough* Tiger P *cough*

  3. Chaz says:

    Extremely good well presented -Chaz

  4. joe says:

    i do wonder if this and the narrow turret were put together could of been pretty lethal i know it took time to turn the turret quickly in the 3 and 4 so hydraulics could of created a slightly better reaction time in combat also would it having hydrostat trasmission make it quieter ?

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