Friday 10 February 2023

Voroshilov Abroad

Soviet tank building was a mystery for foreigners, but the start of the Great Patriotic War lifted the dense veil of secrecy. Depictions of new Soviet tanks first appeared in German intelligence summaries and later in news and propaganda. If the T-34 was a predictable development of Christie’s designs that were already known to American and British engineers, then the heavy KV tank was without an equal or obvious ancestor. As neither the British nor Americans experienced much success with building heavy tanks, these tanks were valuable sources of inspiration. Before too long, they began to receive information directly from their new ally to the east, and even got their hands on the tanks themselves.

Through the fog of war

British, American, and Soviet specialists worked closely together on delivery of military aid to the USSR, but the latter kept mum about their own vehicles even as information began to filter in from German sources. British intelligence documents noted that no tanks like the KV were spotted in Finland during the Winter War. British specialists could only guess at the tank’s characteristics, for instance judging from photos they determined that the roof armour was 30 mm thick, which reliably protected the tank from German aircraft.

A KV-1 tank sent to Great Britain in June of 1943

A KV-1 tank was shown to the British only on December 20th, 1941. The British report classifies it as a medium tank, likely because its full characteristics weren’t revealed. Nevertheless, British tankers had a chance to deepen their understanding of Soviet tank building. The report noted that Soviet T-34 and KV-1 tanks had a lot of parts in common, especially guns and engines. In British opinion, Soviet engineers and technologists dedicated most of their attention to the quality of armour, engine, transmission, and suspension. Everything else was built roughly and almost carelessly. They estimated that the tanks had enough fuel for 150 km of cruising range.

The British report mostly focused on the T-34 tank, but there were notes on the KV as well. The report noted that Soviet heavy tanks used torsion bar suspensions, which were less vulnerable to damage than other types. The ability to start the engine with compressed air was also noted. British specialists wrote down that they didn’t know about any Soviet SPAAGs, but the tank they inspected had an AA machine gun on a pintle mount. There was still a lot they didn’t know about the KV, and even correct information was mixed together with rumours about 100 ton superheavy tanks.

The information made available by the spring of 1942 was more precise. The British were aware that the KV tank weighed 47-48 tons, had 90 mm of armour, and could be equipped with either a 76 or 155 mm cannon and four machine guns: one coaxial, one in the hull, one in the rear of the turret, and one for AA use. Even though the armament of the KV-1 and KV-2 was known, the fact that the different tanks used different turrets was not mentioned. According to British data, the tank was 6.7 m long, 3.3 m wide, 2.7 m tall, and had a clearance of 0.4 m. The track links were 686 mm wide. The KV could cross a 4.5 meter wide trench, 1.2 meter tall wall, and ford a 1.5-1.7 meter deep river. The crew consisted of five men: commander, loader, gunner, driver, and hull gunner/radio operator. This information was incomplete, but quite close to the truth. It was more important than ever to obtain T-34 and KV-1 tanks for study, but the British military mission in the USSR would have to work for another year before this could be achieved.

On July 13th, 1943, a KV-1 tank with the serial number 11306 was loaded on the “Empire Portia” along with a T-34 tank. It was accompanied by 4.3 tons of spare parts, 98 rounds for the main gun (31 AP, 62 HE, and 5 shrapnel) and 3052 rounds of machine gun ammunition, 20 F-1 grenades, a pen knife, and clock. As with the T-34, the waybill was full of translation errors. For instance, the HE shells were marked as AP shot and the machine gun toolkit was labelled “small AA gun sight”. The tank wasn’t fully equipped: it was missing one DT magazine and 13 rounds for the gun. The tarp included with the tank was old and torn.

In the hand of British scientists

The tank made its way to the School of Tank Technology by November 22nd, 1943. The translated manuals arrived even earlier. Both the tank and accompanying documents were studied and a preliminary report was composed by February of 1944. Unlike the T-34, the tank was destined for lengthy trials, so it was not disassembled. British specialists remarked that the tank was roughly built, but surfaces that were vital to the tank’s function were very carefully finished.

KV-1 tank cutaway diagram.

According to the report, the hull design was maximally simplified. Only a few different thicknesses of armour were used. The armour was bent if necessary. The hull floor underneath the fighting compartment was 40 mm thick, which reliably protected the crew from mines. Unlike the T-34, the turret ring was protected with 77 mm thick splash guards on the sides and a 31 mm thick splash guard in the front. The splash guards also doubled as extra hull armour. The main armour was also improved by a 26 mm curved plate on the hull nose.

The hull was welded together. The welding seams looked rough, but inspection showed that they were quite satisfactory. The turret was almost entirely cast. The front was 82 mm thick, the sides were 100 mm thick, and the rear was 97 mm thick. A 30 mm thick roof was welded on top. The cast armour was very soft on the surface, on the order of 174-184 BHN, but hardness grew to 250 BHN with depth. The front 26 mm thick applique plate was also quite soft, 161 BHN. Generally the rolled armour was comparable in hardness to British I.T.80 plate: 239-290 BHN for 75 mm thick plates and 229-259 for 42 mm thick plates. The hardness of 30 mm thick plates varied: the roof was 273-277 BHN, the turret hatch flap was 356 BHN. Despite this variance, the British concluded that Soviet steel manufacturing and heavy industry were highly developed.

Angles of armour plating of the KV-1.

The British report moved onto the tank gun next. As with the T-34, the gun was dubbed “F-34 model 1942”. The gun was weighed at 455 kg. The rifling was uniform at a rate of one rotation per 25 calibers. The description of the gun was identical to the description of the F-34 in the report on the T-34 tank. The report noted that there was a backlash in the elevation mechanism, which made raising the gun difficult. One turn of the flywheel raised or lowered the gun by about 1°, from a maximum depression of -4° to a maximum elevation of 24°30’.

The turret traverse mechanism differed from the one on the T-34. The hand traverse flywheel was located to the left of the gunner. The flywheel was larger than on the T-34, and the gunner’s workspace was roomier, which made the turret easier to turn. However, there was also a backlash here, and the flywheel could turn as much as one revolution before the turret would start to rotate. The turret traverse lock was also located to the gunner’s left.

Armour thickness of the KV-1.

The electric turret traverse was activated with a separate star wheel. It had seven positions: three speeds to the left (corresponding to traverse speeds of 4.02°, 4.16°, and 4.87° per second), three speeds to the right (2.95°, 4.33°, and 5.08°), and neutral. A safety latch locked the turret traverse when it returned to the neutral position.

The description of the machine guns in the report was sparse, but the AA mount thrilled the British specialists. They were particularly happy with its ability to traverse a full 360 degrees regardless of the position of the turret. The Soviet AA machine gun mount was far superior to the Parrish-Lakeman Mounting used on British tanks.

The KV-1’s fighting compartment.

The PT-4-7 and TMFD sights were also studied in detail. The PT-4-7 sight transmitted 26.2% of incoming light, less than the T-34’s periscope. The TMFD periscopic sight let through the same amount: 39.2%. As with the T-34, the testers looked for a clinometer on the gun breech, but could not find one. In addition to the optical sights, the gunner had an observation slit, a periscope, and a pistol port to look through. The commander (according to the British, he doubled as the loader) observed through a periscope, observation slit, pistol port, or PTK panoramic sight, which was installed in a manner similar to the gun sight. The light transmission was worse than the gunner’s periscope: only 25.5%. This periscope also had markings for fire correction.

Even though the British combined the commander and loader into one person, there was still a third crewman in the turret. According to the report, he had quite an interesting array of responsibilities: he was the mechanic, assistant driver, and if necessary also operated the rear and AA machine guns. This jack-of-all-trades surveyed the battlefield through the two rear periscopes and the machine gun sight.

Fighting compartment layout diagram. British specialists made a big mistake when trying to figure out which functions were assigned to which crewman.

The manual stated that the tank carried 111 rounds for the main gun, but the British found only 98: five on each side of the turret and 88 in crates on the floor. The testers did not like the position of the crates. According to them, the crew would have to throw the crates out of the tank along with shell casings as ammunition was expended. The ammunition crates also contained 20 F-1 grenades with fuses in separate bags. There were also 48 disk magazines in the tank for the DT machine guns for a total of 3024 rounds of ammunition. The report indicates that the KV-1 tank was not equipped with smoke dischargers. A rack for a submachine gun was found in the fighting compartment, but the British didn’t find the weapon itself.

The engine was the same as on a T-34, but supercharged to 600 hp. British specialists correctly deduced that the engine descended from a design meant for aircraft and approved of the use of aluminium in its assembly, although they remarked that this would have been an expensive item to produce. The British specialists considered there to be too much empty space in the transmission compartment. According to them, the size and therefore weight of the tank could be reduced without any impact to armour and firepower. The British also didn’t like the heavy hatch flap that had to be opened to service the engine.

Ammunition racks in the turret and the workspace of the assistant driver/mechanic/machine gunner that the British invented.

The British compared the torsion bar suspension to the one on the German Pz.Kpfw.III. They expressed skepticism about use of friction clutches on a 47 ton tank, but further trials showed that it was quite easy to drive. Inspection of the running gear revealed yet another mystery. The tracks were not evenly assembled. Typically links with and without a guide horn alternated, but there were some cases where 3-4 track links with a guide horn were installed in a row. This is yet another reason to disregard the myth claiming that the tanks the USSR sent to its allies were assembled with extra care in order to mislead the UK and US about the quality of Soviet tank production.

As mentioned above, the KV-1 was not taken apart for study. The tank was sent to the Lulworth artillery proving grounds for trials in March of 1944. There it took part in a parade of armoured vehicles. A brochure distributed to attendees briefly listed its characteristics: mass of 47 tons, top speed of 18 mph (29 kph), 75 mm front armour with a 20 mm thick applique plate, 75 mm thick sides. The gun’s muzzle velocity was given as 2231 fps (680 m/s), but no penetration figures were provided. The tank was expected to remain at Lulworth for a long time for gunnery trials and evaluation of the visibility from the tank and convenience of operating its weapons.

 KV-1 tracks with guide horns and without. The latter is assembled from two halves.

Trials began in March of 1944 and dragged on until July. There was no rush to finish the report. It only went to print in October, but in November the process was paused pending additional trials. Meanwhile, the tank was sent to Chobham for repairs. The situation remained unchanged in December and January. In February of 1945 the topic vanished from the proving grounds’ monthly reports. The additional trials for a final report were never conducted. Perhaps, interest in the tank faded. A delegation sent to the Eastern Front back in January of 1944 reported that there were very few KV tanks in active units and only one SPG on its chassis was seen.

The study of the tank did result in a number of questions posed to a Soviet delegation on January 6th, 1944. British tankers asked about whether or not it was reasonable to place fuel tanks in the fighting compartment, to which they received a rather rude response to the tune of “find a better place for them yourselves”. When asked about the lack of indirect fire equipment, the Soviet delegation replied that their tanks are not used in this way. Nevertheless, the British inquired about the ability of the “KV tank with a 6-inch howitzer” to perform this task. Unlike the 76 mm gun, a 152 mm howitzer was still considered a suitable weapon for a heavy tank in 1944.

Fuel system diagram. The location of fuel tanks in the fighting compartment led to some questions from British specialists.

Many questions were asked about the suspension and running gear. The British were quite interested in the steel rimmed road wheels and asked if the tank creates excessive noise and vibrations during movement. The delegation replied that rubber tires are preferable, but no excessive noise and vibrations were observed even with steel wheels.

The delegation was also asked about rough finishing of the torsion bars, use of iron rather than ferodo in brake pad liners, and aluminium radiators instead of copper ones. The answer to these questions was the same: these are limitations of wartime production. The British also criticized the gearbox, specifically the large difference in 3rd and 4th gear speeds and a lack of synchronization. According to the Soviet delegation, this was not an issue for drivers with sufficient training. The British proving grounds staff also wanted to know the reason for the same thickness of armour all-around, to which they received a predictable answer: this was done for all-around protection.

The KV-1’s gearbox. The British criticized its design.

It seemed as though the Soviet delegation was aiming to leave with at least as much information as they shared. As with the T-34, the Soviets reported on rumours that the British were going to produce a copy of the KV with a “6-inch howitzer” (likely the BL 6-inch 26 cwt howitzer), improved gearbox, differential turning mechanism with pneumatic power steering, improved air filters, and air intakes that drew air in from the engine compartment.

The Soviet delegation concluded that the KV was superior to British tanks and it would not be too surprising if they put it into production. Indeed, while the Western Allies had a match for the T-34 tank with the Sherman and to a lesser degree the Cromwell, development of heavy tanks was in a rut. The KV-1 was not entirely suitable for the battlefield by 1944, but study of individual components such as the torsion bar suspension could certainly have helped British designers, who continued to work with archaic designs even after the end of the war. Nevertheless, the KV-1 possibly left some traces in British tank development, such as the Centurion’s prominent turret bustle with a machine gun ball mount.

A KV-1 tank at the Bovington Tank Museum. The slogan written on the turret is incorrect.

Unlike the T-34 tank that arrived in the UK aboard the Empire Portia, the KV-1 tank survives to this day. The tank can be seen at the Bovington Tank Museum in fairly good condition, although the slogan painted on the turret is slightly confusing.

Across the Atlantic

The Americans also obtained a KV-1 tank for inspection. Unlike the British, there was no delay in testing. The tank was sent to the USA from Archangelsk in August of 1942, and trials were already finished by December. A delegation from the Canadian General Staff was also allowed to inspect the vehicle and familiarize themselves with the results of the trials.

A diagram of the “Russian Heavy Tank KV-1”. Note that the author first wrote KB-1 and then wrote the letter V over the B. This mistake was not uncommon in English language documents.

The Americans measured the tank themselves, recording a length of 6.4 meters, width of 3.3 meters, and height of 2.8 meters. The gun elevation range also differed from what the British measured: the maximum elevation was 25° and the maximum depression was -7°. The tank sent to the USA likely didn’t have an AA machine gun mount, as the fourth machine gun included in the tank was described as a spare. The Americans considered these machine guns to be light, simple, and easy to use.

The Americans estimated the front armour to be equivalent to 4 inches (100 mm) with applique armour. They noted that the armour was placed at an angle to improve effectiveness, but the silhouette of the tank was in many ways reminiscent of the British Crusader. The armour was largely cut and welded roughly, but the driver’s observation hatch was very carefully cut and finished.

KV-1 fighting compartment, gunner’s station.

Unlike the British, the Americans judged the crew positions correctly. The report stated that the gunner’s station was quite comfortable. The lack of ability to finely aim the gun using the electric traverse was a drawback, but the American specialists described the turret as very easy to rotate by hand. The gunner had a rotating periscope protected by an armoured cap as well as a telescopic sight.

The loader sat to the right of the gun and had the same periscope as the gunner, just not linked to the gun. American specialists guessed that this enabled the loader to correct the gunner’s fire, an ability which they judged quite useful and even considered trying something like this on their own vehicles. The Soviet tank had no turret basket, and so the crew had to keep their legs perched on a bar when the turret rotated. The upside of this was that it was much easier for the loader to extract ammunition from racks on the floor of the tank. The Americans themselves returned to a similar layout on several tanks, for instance the Medium Tank M4(105).

KV-1 fighting compartment, commander’s station.

The commander sat in the back of the fighting compartment. He could observe the battlefield by looking out of his hatch. Despite its size, it opened easily due to a balancing mechanism.

The V-2K engine was described as putting out 600 hp at 2000 RPM. The Americans knew that the T-34 had the same engine, but with a different fuel system. The tank’s top speed was estimated at 20 mph (32 kph) with a cruising range of 140 miles (225 km). The transmission was described as simple and efficient. The turning mechanism was comparable with that of British tanks. The torsion bar suspension worked well. The tank was a stable firing platform even when driving off-road at high speeds.

KV-1 driver’s station.

The Americans were satisfied with the tank’s performance in trials. The testers liked the torsion bar suspension and spartan layout of the fighting compartment. The finishing of the components was minimal and no unnecessary items were carried inside. All of the internal volume was used for strictly military means.

On August 27th the Aberdeen Proving Grounds received orders to cut out a 6” (152 mm) wide strip from the tank’s turret side and roof, capturing a weld seam. The sample was sent for analysis to the Watertown Arsenal Laboratory. The hardness of the side armour was measured at 285-293 BHN, the roof at 321 BHN, which was harder than typical for American steel of the same thickness. The hardening was considered satisfactory. Hardenability of the armour was high.

V-2K engine as viewed from the turret.

American specialists considered the amount of hot tears in the sample excessive, but judged the composition of the steel as excellent from the point of view of the economy of strategic metals. A high silicon content was noted. This was of interest to the Americans, who tried to create a similar alloy, but found it too difficult to create an alloy with satisfactory characteristics without excessive presence of nonmetallic particles.

The evaluation of the welding was not as good. According to the American specialists a skilled welder could have made a better seam, but the joints were designed well. Their design protected the seams from being hit directly, which compensated for the quality of welding and saved on electrodes.

An excerpt from the report, judging Soviet tank building practice worthy of emulation.

The Americans came to the same conclusion as the British: at first glance, the tank was built hurriedly and poorly. A more thorough inspection showed a well thought out and efficient design. The author called for adoption of similar principles in American manufacturing, as aesthetics rarely win wars.

The KV-1 made a much bigger impression on American tank building than on British. It’s hard to prove direct ancestry, but the Americans soon built their own heavy tank with a torsion bar suspension, cast turret with a pronounced bustle, rear transmission, and similar armour. According to Soviet specialists who spoke to American personnel at the Aberdeen Proving Grounds, the KV-1 tank had a direct impact on the development of T25 and T26 tanks. The latter evolved into the Heavy (later Medium) Tank M26 or Pershing. This tank was the first in a long line of American medium tanks.

The KV-1 displayed at the US Army Ordnance Museum. A patch can be seen where a sample was cut out of the turret for metallurgical testing. Photo by Dmitriy Kiyatkin.

Like the British KV-1, the American one survives to this day. Until 2010 it could be seen at the US Army Ordnance Museum. The tank was moved to Fort Lee when this museum closed. At the moment, it is not accessible to the public.

The author thanks Dmitriy Kiyatkin and Neil Stokes for their contributions to this article.

  • Canadian Military Headquarters, London, (1939–1947) RG 24 C 2
  • Defence Technology Information Center (DTIC)

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