Not Quite a Swallow

 An attempt to "speed up" the Soviet KV-1 heavy tank in March of 1942

Tanks getting heavier during production is a normal phenomenon. Several factors are at play here. One is that requirements for protection increase over time. This is the primary factor for increased mass. Growing mass is also often a consequence for increased requirements for armament. This is usually not a huge increase, but can result in a weight gain of a ton or two. Simplification of the design, especially in wartime, also plays an effect. The T-34 is a typical example. The tank's battle weight was on the order of 27 tons in 1941. The start of the war and subsequent evacuation to the Urals resulted in a large number of simplifications. The T-34 ended up using a large amount of cast components that were much heavier than rolled ones. The tank's mass crossed the 30 ton mark in 1943, but it gained neither better armour nor better armament.

The situation with the KV-1 by mid-August of 1941 was already dire. This was the price paid for applique armour and overall overloading of the chassis.

The situation with the KV-1 heavy tank was similar. Initial requirements called for a weight of 40 tons, but even the U-0, the first KV-1 tank, weighed 42 tons. A pilot tank designated U-7 entered trials in the spring of 1940. This tank already weighed 44 tons. Later, the KV-1 gained a simpler but heavier turret, bow machine gun, and F-32 gun with a heavier mantlet and gun shield. Gradually, the tank's mass climbed to 46 tons by the start of 1941. The GABTU raised a scandal over this, insisting that this could not be. According to them, the tank should have weighed 42.5 tons. However, as the number pi can't become three by decree, neither can 46 tons turn into 42.5. The tank only got heavier from there. Work on applique armour for the KV-1 tank began in the spring of 1941. The design accepted into service weighed 2940 kg. It was approved on June 19th, 1941. The tank's weight reached almost 49 tons. Signs of overloading began to turn up even before this. It was noticed in August of 1941 that all KV-1 tanks have scorching of the final drive clutches. Overheating engines and broken turning mechanisms were common. The applique armour did not remain for long. Tanks with thickened turrets and only frontal applique armour weighed 47.5 tons, but the issue with overloading remained.

ChTZ production tank in Moscow, November 7th, 1941. Officially this tank weighed 47 tons, but that is not the case.

Fall of 1941 marked the start of a new bout of weight gain for the KV-1. The tanks began to receive new ZIS-5 guns with 90 mm thick cast gun mantlets. The thicker armour was because 90 mm of cast armour was about equivalent to 75 mm of rolled armour. Because of this, the KV-1 built at ChTZ (and later ChKZ) weighed closer to 48 tons. Production of cast turrets began in the fall of 1941. They were supposed to be built before the war, but the process only got underway after it began. Like the gun mantlet, this turret was 90 mm thick instead of 75. In practice, the cast turrets could be 100 mm thick, 110 mm, or even thicker. This obviously had an effect on the mass of the tank. Tanks with cast turrets could weigh 50 tons. Officially, the tank still weighed 47.5 tons, but a piece of paper with characteristics is one thing and factory weighing is another. Tanks suddenly clocked in at 50 tons or even more. Like the T-34, elements of the tank had to be simplified, for instance switching to all metal road wheels. All of this compounded issues that arose when production was rapidly increased and resulted in a decline in quality.

The real weights of KV-1 tanks. 49 ton tanks had welded turrets, the ones that weighed more than 50 tons had cast ones.

This all resulted in a decrease in the tanks' reliability and mobility, especially in the snow. The situation wasn't quite as bad as with the T-60 and the KV-1 was still one of the Red Army's best tanks when it came to driving through snow. The problem was that it was supposed to be better at it than the T-34, but reports indicated that the T-34 drives through snow much more confidently, confirming Stalin's remark that the T-34 "flies like a swallow". He definitely was aware of the situation with the KV-1 tank. Stalin had a conversation with V.A. Malyshev' People's Commissar of Tank Production. He had the same conversation with I.M. Zaltsman, Malyshev's deputy and also director of the ChKZ, on January 24th, 1942. Stalin proposed increasing the power of the KV-1's engine to 700 hp and reducing the mass of the tank.

Zaltsman and Kotin proposed installing drivetrain components from the T-222. This proposal was met with opposition from the GABTU.

On January 27th, 1942, Zaltsman and Kotin presented new suggestions to resolve the tank's mobility issues. These were not new. Essentially, ChKZ's designers revived the KV-3 heavy tank. Not the one with blueprint index 223, there was an earlier tank with this name. The tank also known as the T-222 was a further development of the T-150. If not for the rush for mega-tanks, it would have taken the KV-1's place on the assembly line. The T-222 would have had an 8-speed gearbox developed by N.F. Shashmurin, plus a 700 hp engine. A simpler variant was to supercharge the V-2K engine to 650 hp, change the number of teeth on the drive sprocket, and the gear ratio of the final drive. The GABTU considered the "minor modernization" to have a higher priority, pushing the attempt to move the T-222's components into the KV-1 off until a prototype could be tested. This meant that the solution would not be quick. ChKZ kept working on the 8-speed gearbox, a decision that later proved to be absolutely correct. As for the minor modernization, Stalin approved it on January 30th, 1942, with GKO decree 1220ss "On improving performance of KV tanks" and #1221ss "On improving mobility of KV tanks".

One of several photos of KV-1 tank with serial number 10033 that received the V-2KF engine and modified running gear. The tank spent most of its time in repairs.

Two KV-1 tanks were prepared by February 18th, 1942. Both had welded turrets, although tank #6728 had ballast on its roof to match the weight of tanks with cast turrets. Tank #6728 also had drive sprockets with 14 teeth instead of 16 and different final drive gear ratios. A different tank with serial number 10033 received the full set of changes. It received the V-2KF engine with the Nastenko pneumatic regulator. The engine power grew to 650 hp. However, this tank was the one that had the most problems. The tank went out on a test drive on February 18th, where it turned out that the oil temperature reached 125 degrees. One can only imagine what would happen in the summer. The V-2KF engine with serial number #4484 only worked for 20 hours. Attempts to correct this with new radiators and other changes to the cooling system were fruitless. The tank overheated again on a second run, and so the engine was removed from the tank on February 20th.

KV-1 tank #6728 during trials. The tank had a production engine, but 14 teeth on the drive sprocket and an altered gear ratio of the final drives.

Another V-2KF engine with serial number #4433 was installed. The trials were stopped after 5 hours since the overheating didn't go anywhere. The engine was removed on February 23rd and a third V-2KF engine was installed, #6433. This engine lasted even less for the exact same reasons, for 3.5 hours. The engine was removed on February 28th and a centrifugal governor was installed. After this the engine worked for 36.5 hours. The overheating improved with the regulator, but only a little. The oil temperature was still so high that driving at top speed was impossible. This accurately repeated the situation from a year prior where the supercharged engine of the T-150 tank proved itself an excellent tea kettle.

The third tank was a production KV-1 with serial number 25810.

As a result of all the bad luck of tank #10033, it travelled for 529 km in total, 332 of which were counted. The average speed on a highway was 18.7 kph, 17.1 kph on a dirt road, and 12.3 kph off-road. The tank with serial number 6728 was better. In February-March of 1942 it drove for 652.7 km, 464 of which counted. The average speed on a highway was 20 kph, 15.9 kph on dirt roads, and 14.8 kph off-road. The gearbox jammed during trials and the right side final drive broke. Both tanks had broken road wheels and 10033 broke a torsion bar.

This isn't a solid fuel engine, just a KV-1 climbing a hill.

The production KV-1 tank with serial number 25810 drove the longest (710 km, 534.5 of which were counted). The average speed on a road was 27 kph, the average speed on a dirt road was 13.9 kph, and the off-road speed was the same, 13.9 kph. Testers noticed that thanks to the altered final drive ratio and number of drive sprocket teeth, the KV-1 #6728 had advantages over the production tank in difficult terrain. The number of gear shifts was reduced by 10-14 times, which made the transmission work better. Another issue was that the V-2K engine of the KV-1 began to crumble by the end of the trials and had to be replaced. The left brake band, 4 road wheels, and one torsion bar had to be replaced. Since the road wheels broke on terrain where there was no extreme pressure on it, the commission deemed that the issue was with the road wheels.

Altered final drives and drive sprockets of the "fast" KV-1 tanks.

A T-34 tank with serial number 05345 was tested in parallel. It was clear where the "swallow" monicker came from. The average speed on a highway was 42 kph, 30.7 kph on a dirt road, and 24.3 kph off-road. The tank drove on the same snowy terrain, climbed the same hills, and punched through the same anti-tank obstacles that the KV-1 did. Even though the idea of supercharging the V-2K engine was clearly bad, the comparison with the T-34 drove another nail in its coffin.

The performance of the T-34 in snow was incomparable to the KV-1.

The commission reported that the V-2KF engine project can confidently be closed. Even a stronger cooling system did not yield results. The altered final drives and drive sprockets were recommended for production, but this never happened. Meanwhile, the front line troops were complaining about broken gearboxes. This happened due to the design of the gearbox and simplifications that made it less reliable. It became clear in March of 1942 that a deep modernization of the KV-1 was necessary. Stalin admitted this in a meeting with Malyshev, saying that "We made the KV-1 too heavy. This is my fault, your fault is not stopping me." Trials held in February-March of 1942 were the main reasons for the appearance of the KV-13 tank, a heavy tank with the mobility of a medium. Work on the KV-1S, the first less radical version, began at the same time.

Original article by Yuri Pasholok