Monday 23 August 2021

Temperamental Columbina

Even though the Red Army understood the need for a light SPG even before the war, the SU-76's road to the battlefield was long and difficult. Despite popular belief he USSR's manufacturing capabilities were not as great as those of the Western Allies, who didn't need to move their factories thousands of kilometers and set up in an empty field. The front line troops would have been happy to have light tanks, SPAAGs, and tracked APCs, and captured or Lend Lease vehicles of this type were happily used. However, only the SU-76 could be had in sufficient amounts, a vehicle that received mixed impressions.

The simplest way

Formally, T-70 light tanks were produced at three factories, but only the Gorky Automobile Factory (GAZ) was meeting quotas. Factory #38 in Kirov was faring poorly and factory #37 in Sverdlovsk did not manage to set up production of the more complicated vehicle and kept producing T-60 tanks. The situation was even tougher after several air raids on Gorky in the late summer of 1943, which seriously damaged GAZ's output. Since the light SU-12 SPG (later renamed SU-76) was a direct competitor of the T-70, Soviet leadership had to choose which vehicle remained.

The SU-76 had more potential. Its 76 mm gun was effective against enemy armour, while the T-60's 20 mm gun and T-70's 45 mm gun were too weak. The replacement of light tanks with light SPGs meant that the latter still had to carry out tank missions, including close infantry support. However, the SU-76's concept had more to do with the German Marder tank destroyer than the low and well armoured StuG.

The process of the creation of the future SU-76 is told in great detail in Yuri Pasholok's article. It's worth adding that according to documents of the 1434th Self Propelled Gun Regiment (SAP), the first regiment to use the SU-12 in battle, there were more issues with them than just the gearboxes. In part, a report dated March 1st, 1943, says the following:
"For example, when the vehicles turned or switched gears there were cases where the gearbox broke or the clutch came out of alignment due to insufficient robustness. When firing, the mount of the running gear was damaged by the recoil. The idler carriers burst."

In addition to that, one of the subsequent documents described the SU-12's poor off-road mobility, making it impossible to use in forests off roads.

One may also note that in addition to complains about ventilation in the closed top SPG, units that received SPGs without roofs had the opposite complaints. For instance,  a report by the 1440th SAP noted that:

"As a result of use in combat, it is noted that the SU-76 has insufficient armour (and no armour on top), the components are unreliable, including the gearboxes, track pins, and idler carriers."

Need for a machine gun

The SU-76 was healed from its growing pains with time, and the "Columbina" generally showed itself well in the second part of the war as powerful and sufficiently reliable and robust fighting vehicles. Of course, senior officers' questions about the drawbacks of the vehicles had many answers. As all crews of Soviet SPGs, their first and more heartfelt desire was to give the vehicle a machine gun.

"It's desirable to add an AA machine gun with the possibility of using it against ground as well as airborne targets." 

Red Army troops and Czech uprising fighters on a SU-76M driving along the banks of the Vltava in liberated Prague.

Until a machine gun was added, crews had to make do.
"The enemy managed to set a SU-76 aflame near Ratten at a range of 50 meters with a Faustpatrone only because the SPGs were fighting on their own without infantry. Even though each SPG carries a captured machine gun which makes it easier to fight enemy infantry on its own, this is not enough because there are not enough crewmen. In all types of battle and on the march each SPG should be supported by 2-3 submachine gunners."

A good example of this tendency is an episode of fighting in Berlin where Lieutenant Rak, the commander of a SU-76 SPG of the 536th Independent SPG Battalion, seemingly a fan of captured German equipment, arrived in the enemy capital with two MG 34 machine guns. Both broke during the battle and one functional machine gun had to be assembled out of the two. It came in handy when the Germans tried to stop the SU-76s with Goliath remote controlled mines. The SU-76 in front of Rak's SPG was destroyed, but he managed to destroy the next Goliath in time with his machine gun.

A SU-76M in Berlin outside of a destroyed wine store.

The situation where SPGs had to defend themselves on their own was quite common in the second half of the war when SPG regiments were separated from the infantry that they were supporting. For instance, the muddy roads in East Prussia encountered in the spring of 1945 frequently allowed the SU-76 to be the first to enter German cities and towns where Panzerfaust troops hunted every SPG. The solution was to turn the vehicles into improvised troops carriers. The above quote states that 2-3 submachine gunners was the minimum required for self defense, but vehicles often went into battle with 6-8 riders. Unfortunately, reports like this one were not uncommon. The report describes fighting for the Buch homestead in Hungary no later than the winter of 1944-45.
"The enemy opened fire from machine guns during our attack on the settlement and infantry hit the ground. It was not possible to move forward. The commander of the rifle regiment ordered the SU-76 to go forward and destroy the emplacements. The SU-76 crews moved out to carry out the order, but they had no infantry riders. The SU-76 smashed into the enemy trenches without an infantry escort. The infantry did not follow the SU-76. As a result, there was no one to fire at the enemy infantry and the SU-76 were pelted with grenades."

A Degtyaryev mount was added to the SU-76 after all, but all mentions of it in the documents were written after the war. The SU-76 made it to Berlin and Prague without a machine gun.

SU-76M with infantry riders moving out towards the last German positions near the Vistula Lagoon. Vicinity of Heiligenbeil (modern day Mamonovo).

Units that had to fight with the SU-76 in mountainous regions had their own complaints. A report by the 72nd Independent Guards SPG Battalion noted that driving up lengthy slopes and making tight turns resulted in rapid wear of the brake bands. The final drive brake bands had to be replaced every 20-25 km. The repair crews gave a long list of desired improvements. 
  1. The GAZ-203 engines do not provide sufficient power at slopes of 40 degrees.
  2. The main clutch doesn't handle slopes greater than 35 degrees (the conical gears twist up). Final drives wear out as a result of frequent turns and the disks warp. 
  3. The brake bands do not function well at climbs and descents of 30 degrees and burn out. 
  4. The final drives do not handle the load. The teeth of the large cylindrical gear crumble. Idlers and tracks come off during sharp turns on mountain roads. 

There were also a number of complaints about the gun. 

"The gun of the SU-76 has a number of significant defects. After 500-600 shots oil starts to leak out of the rear plug. The SPG then has to be extracted from battle for at least a day for the recuperator to be repaired. When one vehicle fired while tilted the turning mechanism carrier welding seam broke." 

The service life of the weapon may seem long if it is examined outside of the context of the SPGs' careers. In 1944-45 the Red Army followed a wave of artillery barrages to Berlin. Many of them were carried out by SPGs. A report from the 31st Tank Corps noted that the SU-76 carried 60 shells but on average fired 80 per day. In fighting for Torgau (modern day Opava) each SPG fired 110 shots on average. Such peaks were also observed in other units, for instance the 1500th SAP reported that in February and March fighting near Koenigsburg they expended 1.5 ammunition loads per vehicle, or 80-90 shots.

This kind of rate of fire caused one very specific complaint. SPG crews complained that in the heat of battle there was no time to reinsert the spent casings into the ammunition racks. Spent casings littered the SPG's floor and got in the way of the trigger pedal and could also cause the breech to not close fully.

Crew of Senior Lieutenant Aleksey Lalak from the 1729th SAP (3rd Shock Army, 1st Belorussian Front) firing in a settlement on the way to Berlin.

Wishlists composed with war experience in mind indicated that it is desirable to increase the number of HE shells carried on board to 65, since infantry and other unarmoured targets were the main enemy of the SU-76. 15 AP and 10 APCR rounds would be carried in case armoured targets turned up. It was also said that the SU-76 almost never fired indirectly and that the existing panoramic sight should be replaced with a tank one that was more convenient for direct fire.

An interesting note can be found in a report from the 1st Ukrainian Front: "Arm the SU-76 with an 85 mm gun". As we know now, the front line troops and designers had the same ideas.

Not the vehicle's fault

To conclude, we should mention that the main problems with the SU-76 even in the last months of the war were largely caused by incorrect use. Even "brothers on tracks" often aimed to use the SU-76 shoulder to shoulder with tanks. The SPG crews remarked:
"If the SU-76 is used directly near the tanks with 40-50 meters of distance between the tanks and SPGs, and a target appears to the left or the right, the SPG will not be able to fire since its traverse is limited to 13 degrees. The tanks to the left and right will get in the way."
SU-76M during street fighting in Berlin, late April 1945.

As mentioned above, when the SU-76 replaced the T-70 in production it was saddled with the difficult task of close infantry support. Unfortunately, not all combined arms commanders understood the fact that close support doesn't mean "armour goes forward, we will hide behind it" or even "the armour can fight on its own and we'll drop by after". The Red Army often published various directions for use of SU-76 battalions, which clearly stated that:

"SPGs are not tanks. They complete the same objectives that artillery does, not tanks. It is forbidden to use the SU-76 in front of infantry or send them to capture some objective."

Unfortunately, it was often easier to correct technical issues with vehicles than make up for a shortage in training of some commanders...

Original article by Andrey Ulanov.

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