Russo-American Tank Destroyer

One of the key problems with using foreign tanks is keeping a steady supply of spare parts and ammunition. This problem is not exclusive to captured tanks. A similar situation often took place with vehicles that were sent willingly. For example, a lack of ammunition delayed the arrival of American tanks on the battlefields of the Eastern Front by several months. These shortages happened more than once. It is not surprising that arming foreign tanks with domestic guns was a frequently suggested solution.

S-1 (SU-76I), the first design of the TsAKB. The bureau had some experience in re-arming foreign chassis.

It just so happened that the best results in rearming foreign tanks were achieved by the design bureaus of factory #92 and factory #592. The first only offered experimental solutions, but the latter built a small batch of SG-122 SPGs. Specialists from both bureaus were later united in one organization: the Central Artillery Design Bureau (TsAKB). Their first project, the S-1, was a part of rearming a foreign tank (SU-76I). It’s not surprising that new rearmament projects followed, including grassroots proposals.

Armoured Confusion: Mid-war

The history of Soviet wartime armoured vehicles bore several misconceptions. There are many reasons for this. A number of myths came from a lack of information. Sometimes historians' own guesses that had little to do with reality were interpreted as fact. Unfortunately, the authors of some myths are still considered experts to this day and these exercises in fiction are still cited as fact. Initially the author planned on two articles dedicated to misconceptions about the Great Patriotic War, but there were too many misconceptions for 1942-1943, and so the second article won't be the last.

A Captured Chassis

The overall concept of Soviet SPGs was fixed by the start of 1943. The light SU-12 (SU-76) and medium SU-35 (SU-122) were already in production, and work on the heavy KV-14 (SU-152) began in early January. Another, fourth SPG appeared in the spring. Its mass put it in the medium class, but its armament was more appropriate for the light. It was also based on a foreign chassis. This was the SU-76I, an unusual vehicle for Soviet tank building.

SG-122 Conversion

"To the Chief of the Red Army GAU, Colonel-General comrade Yakovlev

Report on the SG-122 SPGs

In December of 1942, factory #40 produced 20 SG-122 SPGs on the chassis of German PzIII and StuG vehicles. Production was later stopped due to defects of the gun mount.

Of the overall number produced, 12 SG-122s were passed on to equip the 1435th SPG Regiment. During fighting on the Western Front, all 12 SG-122s were disabled: of them, 3 were lost irreparably and 9 need factory repairs. Out of those that need factory repairs, 6 vehicles arrived at factory #37 on February 8th, 1943.

SU-76I in Combat

Interestingly enough, the SU-76I, designed as a stopgap measure during the most difficult time for Soviet tank production, continued fighting until at least 1944. The 7th Mechanized Corps lists 13 "SU-76 on T-3 chassis" (compared to only 11 SU-76 on T-70 chassis) among its vehicles (CAMD RF 3436-1-57). However, the comments on its performance weren't exactly great:

"By the start of the operation, all vehicles were ready for battle and moved out to initial positions, except SU-76 SPGs on the T-3 chassis, which did not reach the battlefield and got stuck on insignificant inclines.
...
The battle completely confirmed the low battlefield value of the SU-76 on the T-3 chassis: bad maneuverability, low off-road performance."

A rare photo of a SU-76I in the wild.

Via altyn73.

SU-76I Improvements

"Minutes of a technical meeting at factory #37 on April 29th, 1943, regarding the changes and acceptance of SU-76I vehicles produced in April and acceptance of subsequent vehicles until the approval of working blueprints by GBTU.

Considering the fact that changes approved during technical meetings on March 27th, April 1st, and April 9th required experimental testing, preparation of production, and adjustment to external orders, as a result of which, it is impossible to meet established deadlines, pointless to perform some changes, and necessary to make other changes in greater numbers than anticipated. It was established that:

1. The introduction of a spring which fixes the gun on marches and an indicator that shows the position of the gun is cancelled.
2. It is acceptable to replace the leather belt on the hand trigger with a tarpaulin one.
3. The HEAT shell ballistics table should be moved to the central lamp, attached to the roof. Make these changes on all approved vehicles.
4. An experimental horizontal German-style ammunition rack is to be designed by May 15th, and implemented on all vehicles 15 days after approval.
5. A holder for helmets and the portable lamp will be installed on every vehicle starting with the 10th one. A holder for TPU wires will be installed on every vehicle starting with the 27th.
6. Instead of having a lampshade, the lamp will be moved to the left wall, behind the gunner's seat, on every vehicle starting with the 8th.
7. The commander will have a foot rest on every vehicle starting with the 27th.
8. The gunner's foot rest is cancelled.
9. Tarpaulin cases for the ammunition rack will be included with every vehicle starting with the 8th.
10. Rims for roof hatches will be included on every vehicle starting with the 11th.
11. An additional gun mantlet will be installed on all vehicles no later than May 3rd, starting with the 1st vehicle.
12. External gasoline tanks no less than 100 L in capacity will be added no later than May 3rd, starting with the 8th vehicle.
13. A panoramic backlight will be added to every vehicle.
14. A port for the PPSh will be included in the rear hatch in every vehicle starting with the 11th.
15. Protective glass for vision slits is cancelled, as trials have shown it to be unsatisfactory.

Consider all changes approved at the March 27th, April 1st, and April 9th meetings fulfilled.

Since the factory lacks a drinking water container for the SU-76I that is on blueprints, approve the use of another, flat drinking water container, change the mount, and move it to the engine compartment wall. The medical kit that is currently there should be moved near the horizontal ammunition rack. Make these changes on all vehicles, starting with the first.

Since most PzIII tanks received lack air filters, and since air-oil filters are not being produced, modify the SU-76I to accept dry mesh filters from the ZiS-5 truck produced by MKZ in the month of April."

CAMD RF 38-11369-86

Weakest Link

Using a captured tank you like doesn't only grant you its strengths, but also its weaknesses. Re-equipping the vehicle with domestic components is a partial solution, but in some cases, eliminating the weakest link is just not possible.

"To the Chief of GBTU USA, Major General of the Tank Engineering Service, comrade N.N. Alymov
October 5th, 1943
#148902s

If a tank's engine is removed at the regimental repair yard, no matter how good the rest of the tank is, it cannot be restored and leaving it in inventory would be dishonest. As practice shows, it is impossible to find vehicles in which main components are damaged but engines are not, as the engine is the weakest and most easily worn out part of the vehicle.

I ask you to confirm your agreement to write off vehicles from repair base inventory when the engine is removed.

Factory #37 director, Zelikson
Factory #37 chief engineer, Kozyrev"

The letter doesn't straight up say what tank this is, but the date and factory make it obvious. In the summer of 1943, factory #37 was just ramping up production of the SU-76I, an SPG made using captured StuG and PzIII chassis. Seems that German engine problems weren't exclusive to their larger vehicles.

SU-76I Trials

"To the State Committee of Defense, comrade V.M. Molotov

I report on the results of the proving grounds trials of the experimental SPG that uses a 76 mm tank gun mod. 1940 (F-34) on the chassis of a captured German medium tank PzIII (or StuG) produced by factory #37 according to the GOKO decree issued on January 19th, 1943, #2758ss.

Trials were held at the Sofrino proving grounds from March 13th to March 20th of this year in the amount of 434 shots and 280 kilometers, supervised by the commission led by Lieutenant-General of Artillery, comrade Tikhonov.

The prototype supplied for trials satisfies tactical-technical requirements.

The major characteristics of the 76 mm SU-76 SPG are as follows:

1. Armour:
1. Front: 45 mm at 45 degrees
2. Side: 25 mm at 20 degrees
3. Rear: 25 mm at 20 degrees
4. Roof: 10 mm
2. Ammunition capacity: 95 shells
3. Vertical gun angles: -5 to +15 degrees
4. Horizontal gun angles: +/- 10 degrees
5. Height of the fighting compartment: 1760 mm
6. Bore axis height: 1870 mm
7. Crew: 4

The design of the SPG is very good. The stability when firing is good. The SPG is easy to service. The accuracy is satisfactory. The performance of the vehicle matches that of the PzIII, recorded in the service manual of the latter, and are characterized by insufficient traction of tracks with a slippery frozen road, which results in drifting and slipping. The reliability of rubber tires and drive sprocket is insufficient. This deficiency requires the speed to be limited at 25 kph. When moving on icy or frozen terrain, it is necessary to install V-shaped German spurs. The commission decrees that the SU-76 SPG is adequate for tasks delegated to this type of self propelled artillery, has passed trials, can be recommended for adoption by the Red Army, and must be produced immediately, provided that satisfactory tires can be found or produced domestically, spurs, spare road wheels and sprockets, and careful quality control and re-checking of all PzIII and StuG tanks used in production. 

I consider the tested SU-76 76 mm SPG to be ready for adoption by the artillery branch and mass production.

GAU KA Chief, Colonel-General of Artillery, Yakovlev"

CAMD RF 81-12063-10

Note that the SU-76I weighed only 22.5 tons, compared to 22 tons of a mid-production StuG or 20 tons of a late production PzIII, so excess weight can't be blamed for this fragility of the suspension. 

SU-76I Production Problems

"To the chief of the 1st Department, USA GBTU KA
Engineer-Major comrade Pestov
June 7th, 1943
On the topic of repair stock at factory #37

Report on the general condition of the repair stock at factory #37. In total, from February 1943 to June 5th 1943, 127 captured PzIII tanks and StuG SPGs on the PzIII chassis were delivered to the factory. Of the 127, 27 were delivered by factory #40, 27 from repair base #85, 15 from repair factory #8, 7 from the Kalinin Front, 35 from the South-Western Front, the remaining 15 from the SPG training center. Of those:

1. 24 must be written off.
2. 41 were repaired and converted to SU-76I.
3. 30 are in the process of being converted.

Therefore, as of June 5th, 1943, 32 units are in stock and ready for repairs. Additionally, on June 5th, 1943, a transport arrived from Cherkizovo with 26 additional units. A quick inspection revealed that about 15 vehicles are suitable for repairs, the rest were burnt out and missing parts.

Most vehicles that arrive are either missing parts or have damaged components that cannot be repaired. The issue of drive wheels, magneto generators, gears, brake system gaskets, and others. Due to the incomplete vehicles and the inability to manufacture these parts locally, workers use parts from newly arrived vehicles. As a result, the 32 existing vehicles are "undressed" and missing important parts. In practice, from two vehicles, only one can be built. 

In the first months of production, when the vehicles came primarily from factory #40, repair base #82, and repair factory #8, there was no need to "undress" existing stock for assembly, and the stock was preserved. Currently, most stock comes from the South-West Front in poor condition, completeness, and suitability for repair. "Undressing" factory vehicles means delaying production. I think that the factory cannot meet the quotas assigned to it by the government with its current stock and its condition, unless it is urgently refilled. Additionally, the factory is soon going to have to provide regimental parts kits and repair kits, which will require an increased amount of stock.

Acting Military Representative at factory #37, Engineer-Captain Shitov."

CAMD RF 38-11369-86

A handwritten note at the bottom of the file reads "Measures to increase delivery of PzIIIs have been taken"

Tanks in the Water

The "System of tractor, tank, and armoured car armament of the Worker and Peasant Red Army", defined in 1929, contained 5 main types of tanks, one of which was the reconnaissance tank. One of the characteristics was "all-terrain capability (including water)". However, the tanks developed to match these requirements (T-37, T-38, T-40) were lightly armoured, and armed only with machine guns. Before the T-50's failure as the Red Army's next light tank, an attempt was made to make it amphibious at factory #37.

CAMD RF 38-11355-251

"Currently, work is being done on an amphibious tank with thickened armour based on the existing T-50 tank. In order to finalize the thicknesses of armour plates that can be used, and the tactical-technical characteristics of the vehicle, the factory needs detailed component and overall blueprints of the T-50 tank.

The aforementioned blueprints are stored at the 1st department of NATI, under the index T-135. 

We ask you to order NATI to urgently send the aforementioned blueprints to our factory for temporary use (10-15 days), until we can receive blueprints from factory #174, or to allow our workers to copy the blueprints in NATI."

However, even a T-50 doesn't exactly represent a decisive force. Now, a KV, that's something!

CAMD RF 38-11355-1717

"People's Commissariat of Shipbuilding

Central Construction Bureau #32

To the Chief Tank Directorate

This is a request for the dimensional and weight data on the "KV" type tank, currently active on the front. This data is necessary for the development of a raft that can carry a "KV" type tank on assault operations. Independently from this, we ask what type of tank weighs 46 tons, as it was the tank we were suggested to use for planning. 

We ask the head of the 5th Chief Directorate to confirm the necessity of receiving data on the KV tank.

Central Construction Bureau #32 Chief Fokin

Chief Engineer Nogid"

And then there are more improvised and less fortunate solutions.

Floating a tank over the surface of a water hazard is only one way of getting it across. If the shore is constantly under fire from the enemy, a more creative tactic must be used. During the Nevsky Pyatachok operation to break through Leningrad's blockade, F. Krylov, chief of EPRON (a nominally civilian rescue and underwater engineering organization, included in the Navy at the start of the war) proposed that the heavy vehicle and artillery be dragged underwater. This maneuver was practiced at the EPRON base, but its execution in battle was more difficult: sunken boats and vehicles, as well as constant artillery fire, impeded the divers' work. In total, only a handful of tanks (including two KVs) made it across. Vehicles that sank halfway across the crossing occasionally continued their journey to the other shore in this manner. However, far from all vehicles lost at that crossing were recovered. A number of tanks have been recovered fairly recently by the "Poisk" diving group.

While the river may be an engineer's enemy, it is a historian's ally. If a vehicle is lost in battle, odds are that no one knows where, and even if they do, it can still be hit by artillery, dragged away as scrap, stripped by looters after the war, etc. A vehicle that is lost in a river, especially if the location of the crossing is well recorded, is safe until some archive diggers can find it and recover it. 

"Order to the 58th Independent Tank SPG Regiment

March 30th, 1944

#18

During execution of a combat order, the regiment was performing a march on the route Kremte-Sloboda-Sarny. On February 3rd, 1944, the bridge over Sarny broke, and tank #3038 fell into the river with a crew of 4. 

Tank #3312, while on a march on the Alexandria-Klevan route, was crossing a bridge over the river Goryn' in the region of Tuchino on February 9th, 1944, when the bridge broke, and the tank sank in the river. I order that the following tanks be stricken from the inventory of the 58th Tank Regiment:

1. SU-76I T-3 #3038, engine #3440
2. SU-76I T-3, #3312, engine #542867

as irrecoverable losses during the execution of a combat task.

58th Independent Tank Regiment SPG commander, Major Novikov

HQ Commander, Major Sinchura"

CAMD RF 3783-161190-2

This, of course, is the SU-76I SPG mentioned in this article, the only 100% authentic SU-76I to have been found to date.

SU-76I

I briefly mentioned various Soviet re-arming projects in the past, so let's take a closer look at a successful one, the SU-76I. As was the tradition at the time, the 76 index stands for the caliber of the gun. The I stands for Inostrannaya (foreign). The vehicle was also referred to as SU-76 (S-1) after its gun assembly index, or Sturmgeschütz 76 in German intelligence documents.

"Mass production model of a SU-76I SPG on the chassis of a captured PzIII, designed by factory #37"

CAMD RF 38-11369-1

The Red Army experienced a need for light SPGs armed with 76 mm guns as early as Fall of 1941, but that need was not met until December of 1942, when production of the SU-76 SPG began. Sadly, production was dragging slowly, and the vehicle ultimately ended up a bust. The need for a light SPG didn't go anywhere. In order to meet the army's needs, factory #37 converted PzIIIs and StuGs to use an F-34 76 mm gun in a fixed casemate.

"According to GOKO decree #2758 from January 18th, 1943, factory #37 and TsAKB NKV designed and built an experimental prototype of a SU-76I SPG on the chassis of a captured StuG SPG and PzIII tank, using a stock 76 mm F-34 tank gun.

In March of 1943, the vehicle was tested at the Sofrino proving grounds over 280 kilometers of travel and 434 rounds.

The experimental prototype passed trials, and was recommended for service in the Red Army. The SU-76I SPG was accepted into the Red Army by GOKO decree #2758ss from January 18th, 1943."

CAMD RF 38-11369-1

The SU-76I was a continuation of the SG-122 design, along with some improvements, like sloped armour. Originally, the project called for a ZiS-3 gun (which was later installed on the SU-76), but the only way to provide proper mantlet protection was to use an F-34 in a special frame (indexed S-1). Armour reached 50 mm in the front. The SPG kept its 300 hp Maybach engine. Due to the fact that vehicles of different makes and models served as a base for the SU-76I, various SPGs of this type can look slightly different. It is not known exactly how many of these vehicles were made from StuGs and how many were made from PzIIIs. According to M. Svirin, the total amount of SU-76I and SG-122 vehicles built with captured StuG hulls only equalled eight.

An interesting point: the decree that accepted the SU-76I into service pre-dates its trials by a month and a half. The Red Army must have really needed those SPGs. 611 SU-76I vehicles were built (compared to 550 of the original SU-76 production run).

By the end of 1943, there were almost no SU-76Is left in the army, and in the beginning of 1944, the last of them were transferred to training units. To this day, two SU-76Is remain: an authentic one at Sarny, Ukraine, and one with a restored casemate at the Poklonnaya Gora museum in Moscow. LiveJournal user starcom68 took very many photos of the former one.