7.5 cm SPG (Soviet Hetzer Starr)

Soviet Union (1945-1946)
Self-Propelled Gun – Partial Blueprints Only

Bridging the seemingly non-existing gap between fiction and reality are the post-war Soviet experiments on the German Hetzer Starr technology. The German use of a rigidly mounted gun in an AFV, without any recoil absorption systems, interested the Soviets so much that German engineers that worked on the project were brought in. Studies were made, with blueprints of an AFV hull nearly identical to that of the German Jagdpanzer 38(t) Starr. To what extent these studies went, and if a vehicle was truly intended for testing, is unknown.

Origins

The German Jagdpanzer 38(t), usually referred to and more famously known as the ‘Hetzer’, has become an icon of the latter part of the German armored fighting vehicle arsenal during the Second World War. Its combat record and value impressed many, so much so that production continued post-war in Czechoslovakia as the G-13. It used well sloped armor on all sides, allowing for good protection despite the thin armor plates. The 7.5 cm Panzerjägerkanone 39 L/48 proved to be well suited for a variety of duties.

Truth is that the concept was not entirely new. The Romanians had experimented with the concept of angled walls prior to the Jagdpanzer 38(t), in their Mareşal program. On the other hand, the Soviets began as early as 1940 to work on a very cheap, light self-propelled gun which would use angled plates for better protection. Throughout the war, many variants were drawn up, built and tested, but none ever saw service. They usually tend to be simply called Russian Hetzer(s), a post war designation probably originating from Russian author Mikhail Svirin.

The last of these projects began in late 1945 and sought to offer the Soviet army an extremely cheap vehicle. It used the widely available parts from various obsolete vehicles, of which thousands were leftover after the war effort. The project was inspired from the Hetzer Starr variant, a late war production variant of which less than 20 were built. For this, German designers were brought in.

Jagdpanzer 38(t) Starr

The Jagdpanzer 38t Starr, the basis for the Soviet project, began life almost as soon as the first production versions rolled out. The word ‘starr’ is German for rigid or reinforced. The main theory behind it was to simplify production and lower the weight. Two critical points were explored, namely attaching the gun mount to the hull floor instead of the front plate roof and removing the recoil systems. Other features of the upgrade included replacing the infamous saukopf (English: pigs snout) mantlet with a more angled, bullet-shaped one, and the replacement of the engine, which in turn required a new engine deck and exhaust system.

Changing the gun mount would lower the overall weight of the vehicle, and improve production cost and speed. Another advantage of the system was more internal space for the crew, thanks to the removal of recoil equipment. Both Alkett and Rheinmetall-Borsig had made various gun mounts and trials on the idea, with several outcomes, including a 10.5 cm gun mount.

Yet the entire project proved problematic throughout the development process, as the high recoil shock and stress created gaps, cracks and loosening in the different gun and hull components. These issues were more or less fixed by the end of the war, but how reliable this technology would be in an active fighting vehicle remained an unanswered question.

A production batch of 10 vehicles was ordered in December 1944 and ended in April 1945. Yet only 2 of these vehicles left the Milovice training center.

Development

After the end of the Second World War, the Soviets were able to capture and analyze the Starr, and were impressed by its use of a fixed mount for the gun. Thus, in November 1945, German engineers that worked on the Starr project were brought to the USSR to continue the project for the Soviet military. Studies continued into summer of 1946. As per Russian author Mikhail Svirin, one study was made for the production of a Soviet variant, more or less identical to the original German AFV. The project was commissioned by M.N. Shukin, chief designer at OKB-38.

Previous light Soviet tank destroyer projects were made at the Gorkovsky automobile plant (today known as Nizhny Novgorod), with some ‘Hetzer like’ projects as early as 1942. Work continued throughout the war, with the most advanced being the GAZ-75, also named the SU-85 (not to be confused with the T-34 based SU-85), an 18-tonne tank with 82 mm of frontal armor and an 85 mm D-5S-85 gun. It was designed in just 26 days, with I.V. Gavlov as lead designer. Despite the promising work head engineer of the GAZ factory, A. A. Lipgard canceled all AFV developments at his factory. This was not done as an act of sabotage, but rather because he wanted to prepare the factory for peacetime, when an automobile plant would not need to build tanks. By March 1944, the GAZ-75 (SU-85) was dead.

After the great efforts of the Great Patriotic War, the Soviets found themselves with a large amount of equipment from obsolete light tanks, such as the T-30, T-40, T-60, T-70, and T-80. In a letter from the 10th of April, 1945, Deputy Commander of the Armored and Mechanized Forces, Colonel General of the Tank Forces Korobkov stated:

These vehicles are obsolete, as they have weak armament and insufficient armor. They cannot be used in battle and are only used in training units.
It would take a considerable expense to restore these tanks. Repair units are loaded with repairs of modern tanks, and it is not reasonable to distract them with repairs of obsolete vehicles.
I ask for your permission to use the aforementioned tanks until they require refurbishment, after which they will be written off and disassembled for parts. These parts will be used for light and medium repairs of tanks that are still being used.
These parts proved to be useful for many post-war AFV developments, with certain factories, like OKB IC SV in Moscow, were notorious for using components from these obsolete light tanks. Thus, there is no surprise that, when developing a light and very cheap light self-propelled gun, their components were to be used.

Where exactly the German-Soviet Hetzer Starr design was made is unknown. Equally uncertain is how far the project went. It could have simply been a technology transfer to simply test the viability of a rigidly mounted gun in an AFV. Or, as M. Svirin suggests, it went as far as an SPG designed for the Soviet army. There is not much to back this claim up other than a set of blueprints which lack any sort of automotive components.

Design

Soviet-German efforts largely reproduced the ‘Hetzer Starr’. Drawings of the hull of the project and its gun are almost identical to those of the original German blueprints. Yet some design elements were changed, for example having a single armored side plate instead of two. The drawings do not give a name to the project, and are simply labeled as 7.5 cm KwK self-propelled gun, signed by Captain Dernov. The point was to create a simple and cheap vehicle, in part to replace obsolete light tanks and SPGs. The gun was mounted to the floor of the tank, and able to pivot towards the sides an unknown amount. The crew consisted of 4 men, a commander, gunner, loader, and driver. The crew compartment and the engine were separated by a firewall. Ammunition was probably stowed along the angled side walls.

The armament was of German origin, likely a 7.5 cm PaK 39/1 (L/48). Even the roof periscope was a typical German design, firmly attached to the gun and traversing via a cutout in the roof, covered by an armored plate. The system had a gun elevation of 15° and -8° of depression.

7.5cm Panzerjägerkanone 39 L/48 anti-tank gun armor penetration
(The data was obtained on a firing range. The armor plate was laid back at a 30-degree angle)
	Pzgr.Patr. 39	Pzgr.Patr. 40	Gr. Patr. 38 HL
Shell Weight	6.8 kg	4.1 kg	5 kg
Initial velocity	750 m/s	930 m/s	450 m/s
Range
100 m	106 mm	143 mm	100 mm
500 m	96 mm	120 mm	100 mm
1000 m	85 mm	97 mm	100 mm
1500 m	74 mm	77 mm	100 mm
2000 m	64 mm		100 mm
(Source: Spielberger, Jentz and Doyle)

Armor would have been the same as on the German Jagdpanzer 38(t), with 60 mm at the front, sloped at 30°. The side and rear armor was 20 mm.

Components not drawn in were likely meant to be of Soviet origin, tying in with the aforementioned obsolete light tanks and GAZ experience with designing such light tanks. Propulsion could have been dual GAZ-202 70 hp engines, for a total of 140 hp, or dual GAZ-80 85 hp engines. Considering the similarities with the German Hetzer Starr, the total weight would have been between 15 and 16 tonnes. A hypothetical speed of 40 km/h could have been reached. No details are yet available on the running gear. If already available components were to be used, then 5 to 6 wheels sprung by torsion bars seem logical.

Conclusion

The Soviet experiments on the Hetzer Starr disappeared as fast as they appeared. M. Svirin claims the possibility that progress on a working prototype might have started, but that is highly unlikely. As a matter of fact, the entire project was just an experiment of testing fixed-mounted guns, as a new budget SPG based on WWII equipment was redundant and had no place in the rebuilding Soviet army. A German 75 mm gun had no place in the Soviet army, let alone after the war was already over, clearly not capable of dealing with new Western tanks. The problems of recoil damage to the hull and gun mounts were not yet fixed. The last nail in the coffin came with the development of new and more powerful recoilless guns. While harder to implement in an enclosed AFV, the whole concept was more fruitful than the rigidly mounted gun.

Soviet Hetzer Starr Specifications
Dimensions (approx) (L-W-H)	3.70 – 2.63 – 2.10 m
Total weight, battle-ready	15-16 tonnes
Crew	4 (Commander, Gunner, Driver & Loader)
Propulsion	2x GAZ-202 70 hp enginesOr2x GAZ-80 85 hp engines
Speed	40 km/h (hypothetical)
Suspension	Torsion bar, 5 to 6 wheels per side
Armament	7.5 cm Pak 39 L/48
Armor	Armor: 60 mm angled at 30 deg.20 mm side and rear
No. Built	0, partial blueprints only

Sources:

Stalin’s self-propelled guns M. Svirin
Soviet Hetzers – M. Svirin via Soviet Hetzers (topwar.ru)
The theory of armored errors: the middle of the Great Patriotic | Warspot.ru – Yuri Pasholok
Лёгкие САУ с большими пушками | Warspot.ru – Yuri Pasholok
http://www.pzfahrer.net/starr.html
Tank Archives: Obsolete Tanks – Peter Samsonov
Tank Archives: Soviet Light Tank Destoyers – Peter Samsonov
Tank Archives: An Alternative from Gorky – Peter Samsonov