Monday 3 January 2022

The Final SU-76

The SU-76M (SU-15) light SPG was accepted into service with the Red Army on July 8th, 1943. This was the second most numerous AFV in the Red Army after the T-34/T-34-85. The SU-76M design was good and changed little throughout the war, but feedback from the front lines led to a modernization by the end of it, primarily aimed at improving the protection of the fighting compartment. This vehicle did not receive a new index. It is sometimes referred to as "SU-76M post-war production", but that is not the case. Production began in April of 1945 and lasted for only two months after the end of WW2. These "post-war" SPGs fought during the Soviet-Japanese war of August 1945.

Bring back the roof!

Some historians claim that the appearance of the roof on the SU-12 was met negatively. Allegedly, the vehicle was deemed a gas chamber and the roofs were removed by front line troops. In reality, the situation was different. The roof was only installed on the SU-12 after March of 1943. Vehicles without roofs belong to early production batches. The SU-15M lost its roof due to a need to reduce weight. There was a fear that the extra mass can lead to breakdowns common on the SU-12.

One of the many "homemade" roofs installed on the SU-76M.

The Self Propelled Artillery Directorate (USA) of the GBTU began receiving complaints about the lack of roof starting with late 1943. The absence of a roof led to losses from bullets and shell splinters entering the fighting compartment from above. The front line troops didn't just complain. Reports on installation of various types of improvised roofs began arriving in early 1944.

"Large modernization" SU-76M, NIBT Proving Grounds, September 1944.
"Senior NKTP Inspector comrade Svechkin attached to the Separate Coastal Army reports in his letter #0510 dated January 26th, 1944:

"I report that on the regiment's own initiative the tarp on one SU-76M was replaced with 10 mm thick boiler plate (work on other SPGs is ongoing) since up to 40 crewmen were lost in battle so far, mostly from bomb and shell splinters or blast coming from above. I ask you the reasons why factory #38 continues to install tarps instead of roofs."

This letter refers to SU-76M vehicles with serial numbers 10430, 58411, 310402, 310434, 310436, 58428, 310403 and GAZ model 203 engines produced by factory #38 in the first half of October of 1943.

The vehicle was converted from an ordinary SU-76M build at factory #40.

This was not a singular case. Improvised roofs of all types and shapes were installed by front line workshops. Some only covered the fighting compartment from above, others also covered the rear. The GBTU was opposed to these changes since they made the vehicle heavier, but the front line troops had other ideas. As a result, in the spring of 1944 work began on improving protection of the fighting compartment.

Three hatches were installed in the roof, but they did not completely solve the issue of ventilation.

Normally the design bureau of factory #38 would handle this work, since they initially developed this vehicle. However, this time the work was performed at the Molotov GAZ factory. A reworked variant of the SU-57 SPG was put to trials in June of 1944. The vehicle had a fully enclosed fighting compartment. Periscopic observation devices were added to improve visibility.

Special trials were conducted to determine the comfort of the crew with a fully enclosed fighting compartment. The trials showed that the conditions were satisfactory. Gases in the fighting compartment did not bother the crew. However, conditions were only acceptable if the engine was running and the rear hatch was open. Since there was no special ventilation, work with the engine shut off and hatches closed was uncomfortable. Unlike the SU-12, this vehicle had no ventilation opening in the roof. 

Second variant of the modernization. A DT machine gun is installed in the right firing port.

Work on an enclosed fighting compartment ceased as the factory focused on development of the SU-85A. Factory #40 took over this work. This factory took over light SPG development in general after factory #38 moved to Kharkov. The design bureau led by N.A. Popov had a different approach. Analysis of data from the front lines showed that the crew was most often struck not by splinters from above, but by rifle fire from behind or the sides, since when the roof was initially removed a part of the side and rear armour went with it. The SPG shed a few hundred kilos, but the crew was left more vulnerable. The designers remembered that the SU-76M chassis was sensitive to overloading, so they had to work carefully.

If necessary, the commander's observation port in the front could be replaced with a machine gun. Trials showed that this setup did not work very well.

Two vehicles arrived at the NIBT Proving Grounds in Kubinka in late August of 1944: a large and small modernization. Both were converted from production SU-76M SPGs. Both were built on factory #40's initiative that later gained official support from the GBTU. The large modernization vehicle gained 180 kg and weighed 10,680 kg in total. This was a more thorough overhaul than the SU-57 went through. There were three hatches in the roof: one for the panoramic sight, one for the commander, and one for the gunner. The rear hatch was enlarged. The weight gain was small because the roof was only 4 mm thick. Not a lot, but enough to protect from splinters.

The biggest changes can be seen from the rear. The army approved of the increased height of the rear armour.

The second variant was more interesting. It had no roof, but its mass grew by only 100 kg. There were many more new additions here. The rear armour and rear hatch were much taller and the "pockets" on the sides were almost gone. There were now two firing ports in the rear armour and the ports on teh side changed as well. A special mount underneath the ports allowed a DT machine gun to be installed in them. A DT machine gun with eight magazines was now carried on board at the cost of a reduction of PPSh ammunition from 15 to 12 drum magazines. Another firing port was added to the commander's observation device in the front armour. The tarp support in the rear of the fighting compartment was preserved, but now it had a new function. The machine gun could be mounted here to fire at airborne targets.

DT machine gun in the left firing port.

The SU-76M with a fully enclosed fighting compartment was tested first. The rate of fire was tested with the engine running and not running. The rate of fire was measured at 10-12 RPM. The concentration of CO gas was 0.31 mg/L, 1.5 times the acceptable level. The crew showed some signs of CO poisoning after 15 shots.

The trials of the fully enclosed fighting compartment ended here. The situation could be improved by the addition of an extractor fan, but this was never done. In addition, the visibility from the vehicle with an enclosed fighting compartment was unsatisfactory.

DT machine gun on an anti-aircraft mount.

The testers focused their efforts on the second variant with no roof. Unlike the large modernization, the small one was met much more warmly by the testers. They recommended the taller rear armour for mass production. The appearence of the DT machine gun was also met posititively, but there were some questions about the firing ports. It was hard to aim when firing forward since the sight picture was obscured by the commander's observation device. The side and rear ports had a limited traverse. The traverse of the AA mount was also limited, plus there were some questions about the gun clamp. Testers suggested building an AA turret like on the American GMC T70 tank destroyer, but that was unlikely. This design was too bulky.

Clamp for the DT machine gun used when firing from the firing ports.

The NIBT Proving Grounds staff recommended putting the second variant of the modernized SU-76M into production after the listed defects were corrected. This process took a long time. GAZ and factory #40 were busy with other work in late 1944/early 1945.

Modernization in the last year of the war

Despite a list of defects, the "small modernization" of the SU-76M was a success. The GBTU USA approved a list of trials on December 9th, 1944. However, in early 1945 GAZ designers led by N.A. Astrov were drawn into the modernization process. Their proposal was compared to the one submitted by factory #40 and found to be superior. Their changes were based on experience gained while building the SU-85A. The firing ports and machine gun mount were still taken from the factory #40 project. Blueprints were due by January 25th, 1945, and factories #176 and #177 were expected to start shipping new hulls as of February 15th.

Rear of the SU-76M SPG produced at the Molotov GAZ factory in May of 1945.

The final variant increased the height of the rear plate by 360 mm. The cutouts in the side plates were filled. The rear hatch grew by 360 mm upwards and 210 mm downwards. Like the factory #40 modernization, there were firing ports covered by armoured shutters for the DT machine gun in the sides and rear.  Storage space was allocated for the machine gun as well as racks for nine magazines and two canvas bags with six more. The number of PPSh drums was reduced by 4. The commander's observation device was altered so it could easily fold out of the way and be replaced with the machine gun.

Unlike the factory #40 variant, this vehicle had a new tarp. An arc shaped section could fold up and allow the vehicle to enter battle without the crew having to leave the vehicle and remove the tarp completely. This came in handy when the vehicles had to enter battle straight from a march. The large bench in the rear was split up into two separate seats.

The tarp could flip up quickly and allow the vehicle to enter battle.

Initially delivery of new hulls was expected by March 1st, 1945, but work dragged on. It took time for both the hull producers and the GAZ itself to transition to new production due to a backlog of hulls. The first modernized hulls only arrived at the GAZ in late March of 1945. Factory #40 was in a similar boat.

DT machine gun in the right firing port.

Both factories began to produce the SU-76M with a modernized fighting compartment in April of 1945. Vehicles produced at the GAZ and factory #40 looked differently. For instance, factory #40 SU-76Ms still had no door on the corridor between the driver and fighting compartments. Factory #40 was also working on bags that held 8 machine gun magazines and looking for place to put it. The tarp was also different. Unlike the GAZ vehicles, a portion of factory #40 ones did not have a folding section.

DT mount from the inside.

Officially, the new tarp was only introduced at factory #40 in August of 1945. The vehicles were still different even after the tarp was added. The differences were in the small details, for instance in the travel lock and the new drive's hatch handle introduced at the GAZ but missing on factory #40 SPGs in the spring, summer, and fall of 1945.

Production AA machine gun mount.

There were also some nuances with SU-76Ms produced at the GAZ. The senior military represenative at the factory wrote that the bags installed here fit 7 machine gun magazines instead of 6. The lower shelf of the magazine rack had to be reinforced in May of 1945, since it bent under the weight. Work was also being done on improving the engine and running gear. Small changes were introduced in June, although the work on improvements was undermined by an exodus of designers from the GAZ. The end of the Great Patriotic War was a signal to factory management to slowly wind down war production. This had an impact in July of 1945 when quality of the SPGs dropped and issues with delivery cropped up. Nevertheless, changes continued. New locks for the oil radiator were introduced and the track guard was lengthened by 36 mm. A new gearbox lever was introduced on July 10th.

Tent rails on SU-76M vehicles produced at factory #40 until August 1945 inclusive.

The new fighting compartment made the factories' work harder in April, but production kept up with quotas. GAZ delivered 454 SU-76Ms in April and factory #40 delivered 150. In May the factories delivered 440 and 160 vehicles respectively, and the same number in June. Rates of production began to drop in July. Factory #40 delivered the same 160 vehicles, but the GAZ lowered its output to 420. Production continued to drop as WW2 came to an end. GAZ delivered 250 SU-76M in September and factory #40 delivered 120 vehicles.

SU-76M, June 1945 production. This is how a typical modernized vehicle looked.

Council of People's Commissars Decree #2547-685 was signed on October 6th, ordering the end of SU-76M production at the GAZ and factory #40. 100 more SU-76Ms were assembled in Gorky with the backlog of parts. The last vehicle built here ended up at the NIBT Proving Grounds and can be seen in Patriot Park today. Factory #40 assembled 40 more SU-76Ms in October. In total, 3454 SU-76Ms with a modernized fighting compartment were delivered between April and October of 1945. 744 of them were finished before May 10th, 1945, so it's incorrect to call them "post-war". This increased the number of SU-76M SPGs built to a total of 13,679 vehicles, making it the most numerous SPG in history.

Light long-liver

The first trains with modernized SU-76Ms began to depart the Molotov GAZ towards April 10th, 1945. They were mostly sent to reinforce units on the Soviet-German front, but at least one train with 63 vehicles left for Chita. The vehicles sent as reinforcements did not get to fight. There was normally a month-long delay between when vehicles were shipped out and when they saw battle, so units that received the new SU-76Ms would not have seen action before mid-May.

A modernized SU-76M that fought in the Soviet-Japanese war. This vehicle was produced at the GAZ in April of 1945.

The SU-76M were still built and issued after the war in Europe ended. 1640 vehicles were built and delivered between May 11th and August 1st. A number of them ended up in units that fought in the Soviet-Japanese war. Most units in the Far East used old SU-76Ms, but there are photos of modernized ones.

The vehicles were also used by Self Propelled Artillery Battalions (SAD) attached to rifle divisions. The SADs used in the Far East were organized in a way similar to TO&E #04/434 composed in early 1944. The difference was that in addition to 12 vehicles (3 batteries of 4 guns each) the SAD also had a commander's SU-76M. Rifle divisions finally had organic mobile artillery. The SU-76M was actively used against Japanese forces. There were 952 SU-76Ms in theater on August 5th, 1945: 364 in the 1st Far East Front, 122 in the 2nd Far East Front, and 466 in the Transbaikal Front. The latter had three SPG regiments in addition to the SADs. The SU-76M proved itself to be the most reliable armoured vehicle in the Far East.

SU-76M on parade in Lvov, May 1st, 1947.

The SU-76M was no longer satisfactory by 1945. Even the SU-85B was considered too weak, especially when it came to protection. Requirements were drawn up for a 25 ton fully enclosed SPG with a 100 mm gun. The frontal armour was supposed to protect from the German 88 mm Pak 43. The same chassis would be used to build an SPG with a 122 mm gun in an open fighting compartment. Factory #40 would design these vehicles and a new engine for them. These wonder-SPGs did not progress past drafts. The plans to produce 2925 SPGs with a 100 mm gun and 4352 SPGs with a 122 mm howitzer in 1946-1950 also remained on paper. The military received no new SPGs in this time. As of November 17th, 1947, the Red Army still had 5861 SU-76Ms in service, more than a third of the total production run.

Lvov, November 7th, 1950.

Despite some claims to the contrary, the SU-76M's post-war service lasted for decades. The secret to this long life was simple: development of SPGs, especially light ones, took too long. Schukin's creation had no replacement. Additionally, these SPGs were very reliable, especially the later production ones. The most problematic component was the GAZ-203 engine, and so a new engine called SU-15A was designed in the early 1950s. This was a pair of GAZ-51 truck engines supercharged from 70 to 78 hp, giving a total of 156 hp. The gain in power compared to the GAZ-203 was insignificant, but the increase in reliability was much more noticeable.

The purpose of the SU-76M was unchanged. They were included in the self propelled artillery battalions within rifle divisions. Most of the SU-76Ms in post-war service were the newer vehicles with modernized fighting compartments, which is why many vehicles installed as monuments or in museums in the former USSR belong to this type.

LSD 76/42S on parade in Prague, May 9th, 1949.

The SU-76M also had a rich career abroad. Wojsko Polskie was issued these SPGs during the war, 130 vehicles in total. 52 SU-76M were given to Yugoslavia in 1947. These were chiefly SU-76Ms with modernized fighting compartments. Several of them survive to this day. A number of vehicles were purchased by Albania and Bulgaria in 1947 as well.

In 1949 these vehicles also ended up in the Czechoslovakian army under the index LDS 76/42S. Czechoslovakian industry failed to create anything similar. All they had to show for their work was designs of light SPGs on the Škoda T-17 chassis, but they needed real vehicles. As a result, 70 SU-76Ms were issued to self propelled artillery regiments. One of them can be seen today at the Military Museum Lešany.

Even more SU-76Ms were sold to Romania. 102 vehicles were used by the Romanian army. The MLVM APC was later developed using SU-76M components.

A North Korean SU-76M destroyed during the UN counteroffensive, 1950.

The SU-76M's post-war career in Europe was calm, unlike that of their Asian counterparts. 132 SU-76Ms were shipped to North Korea. These vehicles were actively used in 1950-1953 during the Korean War, especially in its early stages. Fortune turned from North Korean SPGs after the counteroffensive of the UN forces spearheaded by the Americans. The North Korean army's retreat was just as rapid as its earlier advances. Some SU-76Ms were abandoned along with the trains that brought them south. Both SU-76Ms on display in the US right now and the one displayed in Bovington were captured in Korea.

SU-76M in the PLA.

China was the second largest user of the SU-76M. Over 700 vehicles of this type were delivered to the PLA from 1950 to 1954. According to some sources, Chinese SU-76Ms also fought in Korea. China received both SU-76Ms produced in April-October of 1945 and earlier variants. These vehicles were later indexed 115. Soviet vehicles in the PLA received similar codes: the IS-2 was indexed 110, the ISU-152 - 120, the ISU-122 - 121, SU-100 - 122. The SU-76M served in China for a long time, including as a training vehicle. Their career was in many ways similar to that of the T-44M. These SPGs served as chassis for movie tanks. In part, the SU-76M played the part of the Light Tank M3A3 and Japanese tanks.

Vietnamese T-34-85 and SU-76M converted to SPAAGs.

It is not known exactly how many SU-76Ms were shipped to Vietnam in the 1950s. North Vietnam built SPAAGs on their chassis. About two dozen SU-76Ms, mostly modernized ones, were used by Afghanistan until the early 1970s. 

The SU-76M had a successful post-war career. The successful design and high reliability played their part, and the use of automotive components meant that spares were not hard to come by.

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