In defiance of the B-2 – how the Germans made a tank diesel
MB 507
Diesel or carburetor
Where to get it in the 30-40s tank Diesel? There aren't many options. Converting a truck engine into a tank engine is impossible—road-going diesel engines of such size simply weren't available. And there weren't many heavy-fuel engines for ground vehicles anyway. Developing a tank engine from scratch would be very expensive. Economics, as we all know, must be prudent.
In the Soviet Union, for example, they calculated everything. The tank force in the 30s was expected to be the largest in the world, which meant large production runs. This, in turn, significantly reduced the cost of each unit. As a result, in the early 30s, the Kharkov Locomotive Plant initiated the development of an entire series of diesel engines. The smallest of them, the BD-32, was single-cylinder, while the largest, the 18BD-3, had 18 cylinders. The BD-2 of this series proved the most successful, evolving into the legendary V-2 tank diesel. But this development is more the exception than the rule. When a moderate production run is intended, it's worth considering borrowing from others. For example, from engine builders in related disciplines. Where are powerful engines needed? aviation and shipbuilding. There are problems with aviators. The engines are overweight and overpowered.
The first and last tank diesel of the Wehrmacht
You can de-power them, but you can't reduce their volume and weight. Furthermore, aircraft engines typically didn't skimp, making extensive use of scarce alloys, which isn't ideal for tank construction. A key characteristic of aircraft engines was high torque even at low RPMs. While they looked great, excessive thrust required a very robust transmission. Airplanes didn't have this problem—they had propellers. There was nothing to break. Tanks, on the other hand, had delicate clutches, gearboxes, and chassis. And the drivers were often inexperienced. An engine with a moderate increase in thrust as RPMs increased was needed.
Interestingly, the Germans weren't particularly interested in tank diesel engines. There was a guy named Karl Maybach, who managed to gain control of the entire Wehrmacht's armored vehicle engine industry. He supplied the Third Reich with only carburetor engines—or, to be precise, heavily modified automotive power units. Fortunately, this wasn't a problem in Germany. Maybach had very good connections in Hitler's Armaments Office. The Germans still consider this a bottleneck in their military-industrial complex at the time.
Maybach's company failed to supply the army with sufficient spare parts for its engines, and also overcomplicated and continually improved its products. This had a negative impact on production capabilities. This contrasts sharply with the Soviet approach, where any design change was approved, practically at Stalin's headquarters. Time has proven which approach was the more successful.
History It so happened that a diesel engine never appeared in the engine compartment of the entire Panzerkampfwagen lineup. This was not because the Germans were incapable of producing suitable heavy-fuel engines, but because of Karl Maybach's monopoly. However, by the end of the war, the Panzerkampfwagen command realized the full advantages of diesel propulsion, and an order was placed for a suitable engine.
Marine motor
The main character of today's story is the 12-cylinder Mercedes-Benz MB 507 marine diesel engine. This diesel engine was produced in two versions. The smaller MB 507 had a displacement of 42,3 liters and produced rated power of 700 hp and 850 hp at 2350 rpm. The larger MB 507C, with a displacement of 44,5 liters, produced rated power of 800 hp and 1000 hp at 2400 rpm for a limited time.
These engines were developed in the early 30s and belong to the Mercedes-Benz 500 series of diesel engines. They were developed for the Kriegsmarine for a wide range of vessels. The first engines in the series—the 700-horsepower MB 500—were intended for the Schnellboote high-speed attack boats. The 1500-horsepower MB 501 was built for submarines. The U-180 and U-190 were equipped with six of these engines each, but only for a short time. They proved inconvenient for submariners and were replaced by MAN diesels.
Mercedes-Benz 507
Interestingly, the future MB 507 tank diesel engine was developed for the Leichte Schnellboote torpedo boat and was based on the Daimler-Benz DB 603 aviation diesel engine. To avoid confusion, marine diesel engines are called Mercedes-Benz, and aviation diesels are called Daimler-Benz, but they were developed by the same company. Strictly speaking, the MB 507 was a hodgepodge—the Germans added components from another aviation diesel, the DB 602. In short, they tried to reduce the cost of the finished product as much as they could.
But there were also many differences. The 507 had a different crankcase, no turbocharger, and a normal turbo setup, with the crankshaft at the bottom and the cylinders and pistons at the top. The marine version was the opposite. The 700-horsepower version of the engine was quite compact, weighing only 850 kg.
A direct comparison of the Mercedes-Benz engine with the Soviet B-2 would be imprecise, as they were products of different classes. The domestic engine produced 450-500 hp with a displacement of 38,88 liters. It weighed comparable amounts, between 750-1000 kg, depending on the version. The German engine was 200 hp more powerful with a larger displacement of 42,5 liters. The Mercedes was far more advanced, but it was only suitable for a comfortable war, and was also much more labor-intensive to manufacture and expensive. In short, the B-2 won the war, although the 507th didn't show up for it, essentially. It didn't make it in time.
Mouse
But the Mercedes-Benz 570 went down in history as the only German mass-produced tank diesel engine. The 12-cylinder engine was originally designed for the gigantic Karl-Gerät self-propelled mortars. Three units received it immediately, and over time, the remaining chassis in the series were converted to its more powerful MB 507C version. The engine's combat career in the 600mm Karl-Gerät self-propelled mortars was inextricably linked with the largest sieges of World War II.
Due to the mortar's colossal 124-ton mass, the diesel engine was used in a very specific way: it wasn't designed for long marches (mortars were transported to the front by rail), but rather for independent drives to firing positions, positioning in caseniers, and rough horizontal guidance, which was accomplished by rotating the entire vehicle hull. To improve reliability in these extreme conditions, the MB 507C's power was artificially limited to 580–590 hp, allowing the enormous engine to deliver consistently high torque at low speeds, not exceeding 10 km/h.
These engines saw their most active service during the siege of Sevastopol in 1942. The "Thor" and "Odin" mortars (chassis #III and #IV), initially equipped with diesel engines, methodically pounded Soviet fortifications and coastal battery #30. Later, in 1944, the "Tsiu" mortar (#VI), also equipped with the MB 507C, was used to suppress the Warsaw Uprising, where the diesel engine ensured the giant's maneuverability through the city's ruins. By this time, almost the entire series had been converted to the MB 507C, as it proved significantly more efficient and reliable than the older gasoline engines. The "Karls" often failed due to overloaded chassis, but the Mercedes-Benz engines themselves demonstrated enviable durability, operating in the monstrous dust and vibrations of firing two-ton shells.
Karl-Gerät
During the development of the "supertank" projects, the MB 507 was also considered as the primary powerplant. It was planned for the 70-ton Löwe (VK 70.01) and the prospective super-heavy E-100, where the diesel engine was intended to compete with Maybach gasoline engines. The pinnacle of the line's development was the turbocharged MB 517. Although the MB 517 provided the enormous vehicle with better power-to-weight ratio and reliability than its competitors, it was an extremely sensitive engine: the high boost ratio combined with the Maus tank's enormous weight led to critical overloads on the crankshaft and bearings. The turbocharger required precise tuning and high-quality maintenance, which was impossible given the collapse of German industry in 1945.
It was this engine that was installed in the second Maus prototype (V2), replacing the DB 603 gasoline engine. It was this engine that was responsible for the tank's demise at Zossen, when seized pistons turned the 188-ton vehicle into an immobile heap of iron. It happened like this: in mid-March, as the Red Army was already approaching the capital of the Reich, it was decided to use the tank as a mobile firing point to cover strategic targets. Under its own power, the Maus covered approximately 14 kilometers to Stammlager, located near Zossen, where the German General Staff headquarters was based. The tank took up a position at the crossroads between Zossen and Wünsdorf, effectively becoming part of the outer defensive ring of Berlin. However, the "heroic" battle never happened: on April 21, 1945, while attempting to change positions or advance toward the advancing units of the 3rd Guards Tank Army, the super-powerful Mercedes-Benz diesel engine succumbed to the enormous load. Thus ended the tank career of the Mercedes-Benz marine diesel engine.
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