Kliment Voroshilov tank

By 1942, when the Germans were fielding large numbers of long-barrelled 50 mm and 75 mm guns, the KV's armour was no longer impenetrable, requiring the installation of additional appliqué armour. The KV-1's side (favourable approach: 30° at 300–500 m distance), top, and turret armour could also be penetrated by the high-velocity Mk 101 30 mm cannon carried by German ground attack aircraft, such as the Henschel Hs 129.[13] The KV-1's 76.2 mm gun also came in for criticism. While adequate against all German tanks, it was the same gun as carried by smaller, faster, and cheaper T-34 medium tanks. In 1943, it was determined that this gun could not easily penetrate the frontal armour of the new Tiger,[14] the first German heavy tank, one of which was captured near Leningrad. The KV-1 was also much more difficult to manufacture and thus more expensive than the T-34. In short, its advantages no longer outweighed its drawbacks.

Nonetheless, because of its initial superior performance, the KV-1 was chosen as one of the few tanks to continue being built following the Soviet reorganization of tank production. Due to the new standardization, it shared a similar engine and gun as the T-34 (the KV used a 600 hp V-2K modification of the T-34's V-2 diesel engine, and had a ZiS-5 main gun while the T-34 had a similar F-34 main gun), was built in large quantities, and received frequent upgrades.

When production shifted to the Ural Mountains "Tankograd" complex, the KV-2 was dropped. While impressive on paper, it had been designed as a slow-moving bunker-buster. It was less useful in the highly mobile, fluid warfare that developed in World War II. The turret was so heavy it was difficult to traverse on uneven terrain. Finally, it was expensive to produce. Only about 300 KV-2s were made, all in 1940-41, making it one of the rarest Soviet tanks.

KV-1 produced in 1942, displayed in the Finnish Tank Museum in Parola

As the war continued, the KV-1 continued to get more armour to compensate for the increasing effectiveness of German weapons. This culminated in the KV-1 model 1942 (German designation KV-1C), which had very heavy armour, but lacked a corresponding improvement to the engine. Tankers complained that, although they were well-protected, their mobility was poor and they had no firepower advantage over the T-34 medium tank.

In response to criticisms, the lighter KV-1S was developed, with thinner armour and a smaller, lower turret in order to reclaim some speed. The KV-1S had a commander's cupola with all-around vision blocks. It also had a sophisticated planetary transmission that significantly increased the reliability, and allowed use of more efficient regenerative geared steering, unlike the solely clutch and brake steering systems used by the Panzer III, IV and T-34 and previous KV tanks. Its reduced weight allowed it to achieve a top speed of 43.3 km/h. Over 1,300 were built before production ended in August 1943.[15] Although the KV-1S was, according to some, the best of the KV tanks, overcoming its predecessors' problems (at a cost of losing the heavy armor that made the earlier tanks so valuable, making it more of slow medium tank than a heavy tank), more modern tanks were already in sight.[16] Up-arming the regular turret of the KV-1S with an 85 mm S-31 resulted in the KV-1S-85. This was rejected as it came with the unacceptable loss of a dedicated commander, reducing the turret crew to two (unlike the 3-man turret fitted to the T-34/85).[17] However, the thinning-out of the armour called into question why the tank was being produced at all, when the T-34 could seemingly do everything the KV could do and much more cheaply. The Soviet heavy tank program was close to cancellation in mid-1943.

The appearance of the German Panther tank in the summer of 1943 convinced the Red Army to make a serious upgrade of its tank force for the first time since 1941. Soviet tanks needed bigger guns to take on the growing numbers of Panthers and the few Tigers.

A stopgap upgrade to the KV series was the short-lived KV-85 or Objekt 239. This was a KV-1S with the new turret from the Object 237 (IS-85) still in development, mounting the same 85 mm D-5T gun as the SU-85 and early versions of the T-34-85 (not yet in production at the time). The 85 mm proved capable of penetrating the Tiger I from 1000 m and the demand for it slowed production of the KV-85 tremendously, only 148 were built between August and October 1943.[18] Soviet industry was therefore able to produce a heavy tank as well armed as the Tiger I before the end of 1943. Although the KV-85 was an excellent opponent to the Tigers and Panthers, it was a stopgap and thus was built in small numbers.[15] The complete Object 237 was accepted into service as the IS-85 and was produced in the autumn and winter of 1943-44; they were sent to the front as of October 1943 and production of the IS-85/IS-1 was stopped by the spring of 1944 once the IS-122/IS-2 entered full-scale production.

A new heavy tank design entered production late in 1943 based on the work done on the KV-13. Because Voroshilov had fallen out of political favour, the new heavy tank series was named the Iosif Stalin tank, after the Soviet leader Stalin. The KV-13 program's IS-85 prototype was accepted for production as the IS-1 (or IS-85, Object 237) heavy tank. After testing with both the 100 mm D-10 and 122 mm guns, the D-25T 122 mm gun was selected as the main armament of the new tank, primarily because of its ready availability and the effect of its large high-explosive shell when attacking German fortifications. The 122 mm D-25T used a separate shell and powder charge, resulting in a lower rate of fire and reduced ammunition capacity. While the 122 mm armour-piercing shell had a lower muzzle velocity than similar late German 7.5 cm and 8.8 cm guns, proving-ground tests established that the 122 mm could penetrate the frontal armour of the German Panther tank at 2500 metres[19] and the HE shell would easily blow off the drive sprocket and tread of the heaviest German tank or self-propelled gun. The IS-122 replaced the IS-85, and began mass production as the IS-2. The 85 mm gun saw service in the lighter SU-85 and T-34-85.

The Soviets did not recognize different production models of KV-1 during the war; designations like model 1939 (M1939, Russian: Obr. 1939) were introduced later in military publications. These designations, however, are not strict and describe leading changes, while other changes might be adapted earlier or later in specific production batches. Designations like KV-1A were applied by the Germans during the war. All tanks in the series were heavily based on the KV-1.

KV-1 model 1939

A KV-1B at the Bovington Tank Museum

• KV-1
  • Model 1939 – First production models, these tanks were prone to frequent breakdowns, but were highly resistant to anti-tank weapons during the Winter War. Armed with the 76 mm L-11 tank gun, recognizable due to a recuperator above a barrel. Most tanks were lacking the hull machine gun. 141 were built.
  • Model 1940 (German designation: KV-1A) – Used the F-32 76 mm gun and a new mantlet. The main production model by the time of the German invasion.
  • Model 1940 s ekranami ("with screens") or KV-1E – with additional bolted-on appliqué armour and F-32 gun.
  • Model 1941 (German designation: KV-1B) – Up-armoured with 25–35 mm (0.98–1.38 in) added to the turret, hull front and sides. Turret was now cast instead of welded. This tank was armed with the longer-barreled ZiS-5, tank gun.
  • Model 1942 (German designation: KV-1C) – Fully cast turret with thicker armour or welded turret with thicker armour, again up-armoured, using an improved engine and the 76 mm ZiS-5 tank gun.
  • KV-1S – A variant with higher speed, but thinner armour. A new, smaller, cast turret and redesigned rear hull with a new planetary transmission. 1370 built.

The KV-2 heavy artillery tank's 152 mm howitzer was housed in an enormous turret. This prototype differs from the production version in several ways. It was called the Dreadnought by its crews.[20]

Comparison of selected KV tank chassis variants.

• KV-2 (334) – A heavy assault tank with the M-10 152 mm howitzer, the KV-2 was produced at the same time as the KV-1. Due to the size of its heavy turret and gun, the KV-2 was slower and had a much higher profile than the KV-1. Those captured and used by the German Army were known as (Sturm)Panzerkampfwagen KV-II 754(r). Few were produced due to its combat ineffectiveness, mainly the decreased speed due to the weight of the new gun and turret. Due to an increase in turret weight from the expanded dimensions and a heavier gun, the turret traverse mechanism could work only on level ground.
• Т-150 (Object 150) - One of a pair of designs requested 17 June 1940. Armour specified at 90 mm, which caused weight to reach 50 tons, so the 600 hp V-2K was replaced with the 700 hp V-5 engine. In addition to the improved armour, the turret had a cupola but otherwise followed the design of the KV-1. One prototype was constructed in 1941 and was destroyed defending Leningrad. On 15 March 1941 the design was approved for production as the KV-3.[21][22]
• T-220 (Object 220) - One of a pair of designs requested 17 June 1940. Longer chassis with 7 rollers per side. Armour specified at 100 mm. Prototype trialled with V-2PUN and V-2SN engines. but suffered engine and suspension problems. New diamond-shaped turret fitted with 85 mm F-30 cannon, but development changed to fitting 107mm F-39 instead. One prototype was constructed in 1941, but did not enter serial production.[21][23]

• KV-3 (Objects 150, 220, 221, 222, and 223) - Designation initially approved 15 March 1941 for production version of Object 150 tank design. Further developments were made on the basis of the Object 220, in the form of the Object 221 (with an 85 mm gun), Object 222 (with the F-32 76.2 mm gun) and Object 223 (built to develop a new conical turret to housing the 107 mm gun, now specified to be the ZiS-6 cannon). Series production was intended to start in late 1941, but the German invasion of the USSR halted these plans and the only prototype hull was destroyed. The design was accepted for service May 1941 and was to have entered production at the Kirovsky Plant in August 1941, but the German invasion forced this to be abandoned.[21][24]
• KV-4 (Object 224) - A project for a super-heavy tank. About 20 different designs were proposed, but it was cancelled due to the outbreak of the war. Different versions would have been between about 85 and 110 tonnes. Armour from about 120 to 190 mm. Armament consisted of the 107 mm ZiS-6 cannon. Different variants had various auxiliary weapons: 45 mm, 76 mm cannons, machineguns and flamethrowers in addition to the main gun.[25]
• KV-5 (Object 225) - A cancelled project for a super-heavy tank. Armament was to be a 107 mm ZiS-6 gun in a large turret and machine-gun in a small secondary turret. Weight was projected as about 100 tons, and the tank was to have 150–180 mm of armour. Project development began in June 1941, however was cancelled due to the Siege of Leningrad, in which all developmental operations at the Kirov Plant were halted. The project fell out of favour from the more advanced heavy tank designs, and no prototype was built.[25]
• KV-7 (Object 227) (also called U-13). - Experimental self-propelled gun. armed with 3 cannons: two 45 mm model 1932/34 and one 76 mm F-34. 200 rounds of ammunition was carried for the 45 mm guns and 93 rounds for the 76 mm gun, and the tank had 100 mm of frontal armour. One unit was produced and tested in 1941.
• KV-7-2 (improved variant) (also called U-14) had two 76 mm F-34 cannons, and 85 mm of frontal armour. Vehicles were not taken in service primarily because they could not fight tanks (the KV-7s had only 15 degree gun traverse to each side) and could not combat concrete bunkers due to the small caliber of the guns. After the failure of the KV-7 it was decided to put one 152 mm gun in the casemate instead of three smaller guns; this led to the development of the SU-152.
• U-18 - Experimental self-propelled gun. KV-7 armed with 152 mm ML-20 cannon. Vehicle was projected in 1941. Wooden mockup was constructed. Project was cancelled, but this vehicle was a first step towards SU-152 design.
• S-51 (also called U-19) - Experimental self-propelled gun projected by the Grabin Artillery Projects Central Department armed with the 203 mm howitzer M1931 (B-4) cannon in a KV-1S hull. The vehicle was to have 75 mm of frontal armour, 60 mm on the side, and the roof was to be 30 mm (the roof would have been removable to facilitate loading). It was projected to weigh 66 tons, one prototype passed by the testing grounds in the spring of 1944 but it was not very successful and was cancelled within a year.
• SU-152 - See SU-152. Heavy assault gun based on the KV-1S chassis using 152 mm ML-20 gun.
• ZiK-20 - The ZiK-20 was very similar to the U-19 (S-51), but had 105 mm of frontal armour, and 75 mm of side armour and was to mount a ML-20 gun. By the time was wooden mockup was made the KV-1 was phased out of production. However just before the project was cancelled a blueprint was drawn up to equip the ZiK-20 with a Br-2 152.4 mm gun; and to offset the weight the frontal armour was to be reduced to 75 mm (or 60 mm on the KV-1S chassis).
• SU-203 - SU-152 equipped with 203 mm M-4 mortar. Never built.
• KV-8 (42) – A KV-1 fitted with the ATO-41 flamethrower in the turret, beside a machine gun. In order to accommodate the new weapon, the 76.2 mm gun was replaced with a smaller 45 mm Gun M1932, though it was disguised to look like the standard 76 mm (the cannon was placed inside a 76 mm tube).
  • KV-8S (25) – The same as KV-8, but based on KV-1S. Equipped with ATO-42 flamethrower (improved version of ATO-41).
  • KV-8M - Upgraded version of KV-8S. Equipped with two flamethrowers. Two prototypes were constructed.
• KV-9 (Object 229) - A KV-1 with short 122 mm U-11 cannon. One prototype was constructed and proved in 1941.
• KV-10 (Object 230) - Also known as KV-1K. A KV-1 with 4 rocket launchers on the sides of hull. Each launcher contained two 132 mm M-13 rockets. Early variant of KV-1K had two launchers on the back of hull, each contained 6 rockets. One prototype was constructed and tested in 1942. Not taken in service.
• KV-11 (Object 231) - KV-1 armed with 85 mm F-30 cannon. Projected in 1942. Not built.
• KV-12 (Object 232) - Experimental chemical tank. Was equipped with 4 external toxin tanks on the back of chassis. Tanks surrounded with 30 mm armour. Not taken in service.
• KV-13 (Object 233) - Prototype of a medium tank. Designation for an advanced redesign of the KV series, which resulted in the production of the IS series.
  • IS Model 2 - A KV-13, with turret and armament from KV-9. One prototype was constructed and proved in 1943. Tank had lost competition to IS Model 1 and was not taken in service.
• KV-14 (Object 236) – Prototype designation for a 152 mm self-propelled gun, accepted for service as the SU-152.
• KV-85 (Object 239) – A KV-1S with the 85 mm D-5T cannon in a new turret, with the ball mounted hull machine gun removed and the hole welded shut, 148 of these tanks were produced in the second half of 1943 until the spring of 1944; they were a stopgap until the IS tank series entered production.[26]
  • KV-85G - KV-1S with 85 mm S-31 cannon. Turret and mantlet remained from conventional KV-1S. This variant was a competitor of KV-85 during proving. It lost the competition and was not taken in service.
  • KV-122 - A KV-1S with short 122 mm S-41 howitzer. One prototype was made in 1943. Not taken in service.[27]
  • KV-100 - A KV-85 with the 100 mm S-34 cannon. One prototype was made in 1944. Not taken in service.
  • KV-122 - A KV-85 with the 122 mm D-25T cannon. One prototype was made in 1944. Not taken in service.
  • KV-152 - Proposal to fit a 152 mm gun into the turret of a KV-85. Nothing became of the project.

A KV-1 on fire, knocked out near Voronezh in 1942.

A KV-1 or KV-2 tank (accounts vary) advanced far behind the German lines after attacking a column of German trucks. The tank stopped on a road across soft ground and was engaged by four 50 mm anti-tank guns of the 6th Panzer Division's anti-tank battalion. The tank was hit multiple times but it fired back, disabling all four guns. A heavy 88 mm gun of the German division's anti-aircraft battalion was moved about 730 metres (800 yd) behind the tank, but was knocked out by the tank before it could score a hit. During the night, German combat engineers attempted to destroy the tank with satchel charges, but were unable to, despite possibly damaging the tracks. Early on the morning of 25 June, German tanks fired on the KV from the woodland while an 88 mm targeted the tank from its rear. Of several shots fired, only two penetrated the tank. German infantry then advanced, with the KV opening machine-gun fire against them.[30] The tank's resistance was finally ended by grenades thrown into the tank's hatches. According to some accounts, the crew was buried by the German soldiers with full military honours; in other accounts, the crew escaped during the night.[30]

General Erhard Raus was Commander of the 6th Panzer Division's Kampfgruppe,^[f] the unit delayed by the lone vehicle. He described it as a KV-1, which was damaged by several 88mm anti-tank gun shots fired from behind the vehicle while it was distracted by Panzer 35(t) tanks from Panzer Battalion 65, and the KV-1 crew were killed by members of a pioneer unit who pushed grenades through two holes made by the gun while the turret began moving again, the other five or six shots having not fully penetrated. Apparently, the KV-1 crew had remarkably only been stunned by the shots which had entered the turret. Afterwards, they were buried nearby with military honours by the German unit.[31][lower-alpha 1]

On August 14, 1941, the vanguard of the German 8th Panzer Division approached Krasnogvardeysk (Gatchina) near Leningrad (St Petersburg), and the only Soviet force available at the time to attempt to stop the German advance consisted of five well-hidden KV-1 tanks, dug in within a grove at the edge of a swamp. KV-1 tank no. 864 was commanded by the leader of this small force, Lieutenant Zinoviy Kolobanov.

German forces attacked Krasnogvardeysk from three directions. Near Noviy Uchkhoz settlement the geography favoured the Soviet defenders as the only road in the region passed the swamp, and the defenders commanded this choke point from their hidden position. Lieutenant Kolobanov had carefully studied the situation and readied his detachment the day before. Each KV-1 tank carried twice the normal amount of ammunition, two-thirds being armour-piercing rounds. Kolobanov ordered his other commanders to hold their fire and await orders. He did not want to reveal the total force, so only one exposed tank at a time would engage the enemy.

On August 14, the German 8th Panzer Division's vanguard ventured directly into the well-prepared Soviet ambush, with Kolobanov's tank knocking out the lead German tank with its first shot. The Germans falsely assumed that their lead tank had hit an anti-tank mine, and failed to realize that they had been ambushed. The German column stopped, giving Kolobanov the opportunity to destroy the second tank. Only then did the Germans realize they were under attack, but they failed to find the source of the shots. While the German tanks were firing blindly, Kolobanov knocked out the trailing German tank, thus boxing in the entire column.

Although the Germans correctly guessed the direction of fire, they could only spot Lieutenant Kolobanov's tank, and now attempted to engage an unseen enemy. German tanks moving off the road bogged down in the surrounding soft ground, becoming easy targets. 22 German tanks and 2 towed artillery pieces fell victim to Kolobanov's No. 864 before it ran out of ammunition. Kolobanov ordered in another KV-1, and 21 more German tanks were destroyed before the half-hour battle ended. A total of 43 German tanks were destroyed by just five Soviet KV-1s (two more remained in reserve).

After the battle, the crew of No. 865 counted a total of 135 hits on their tank, none of which had penetrated the KV-1's armour. Lieutenant Kolobanov was awarded the Order of Lenin, while his driver Usov was awarded the Order of the Red Banner. Later on, former Captain Zinoviy Kolobanov was again decorated by Soviet authorities, despite having been convicted and downgraded after the Winter War for "fraternizing with the enemy." After the end of World War II, Lieutenant Kolobanov served in the Soviet occupation zone in East Germany, where he was convicted again when a subordinate escaped to the British occupation zone, and was transferred to the reserves.

The battle for Krasnogvardeysk was covered up by Soviet propaganda. A monument dedicated to this battle was installed in the village of Noviy Uchkhoz in 1980, at the place where Kolobanov's KV-1 was dug in, due solely to the demands of the villagers. Unfortunately it was impossible to find a KV-1 tank, so an IS-2 heavy tank was installed there instead.[33]

The Soviet victory was the result of a well-planned ambush in advantageous ground and of technical superiority. Most of the German tanks in this battle were Panzer IIs, armed with 20 mm guns, and a few Panzer IIIs armed with 37 mm KwK 36 L/46.5 guns. The German tank guns had neither the range nor the power of the 76 mm main gun of a KV-1, and the narrower track width of the German tanks caused them to become trapped in the swampy ground.

Some KVs remained in service right up to the end of the war, although in greatly diminishing numbers as they wore out or were knocked out.

The 260th Guards Heavy Breakthrough Tank Regiment, based on the Leningrad front, operated a number of vintage 1941 KV-1s at least as late as the summer of 1944 before re-equipping with IS-2s.

A few KV-85s were used in Crimea in the summer of 1944.

A regiment of KVs saw service in Manchuria in August 1945.

The Finnish forces had two KV-1s, nicknamed Klimi, a Model 1940 and Model 1941, both of which received minor upgrades in their service, and both of which survived the war.

Romanian forces captured one KV-1 as of 1 November 1942 and one more in March 1944.[34]

• German Tiger I
• United States M6 heavy tank
• British Churchill tank

• Raus, Erhard (2003). Panzer Operations: The Eastern Front Memoir of General Raus, 1941-1945. Translated by Steven H. Newton. Da Capo Press. ISBN 978-0-306-81247-7.
• Stokes, Neil (2010). KV Technical History & Variants. Canada: Air Connection Hobby. ISBN 978-0-9781091-2-7.
• Vollert, Jochen (2005). Tankograd Militar Fahrzeug - Special No. 2003 Soviet Special - KV-1 Soviet Heavy Tanks of WWII - Late Variants. Tankograd Publishing.
• Zaloga, Steven J; James Grandsen (1981). Soviet Heavy Tanks. London: Osprey Publishing. ISBN 0-85045-422-0.
• Zaloga, Steven J. and James Grandsen (1984). Soviet Tanks and Combat Vehicles of World War Two. London: Arms and Armour Press. ISBN 0-85368-606-8
• Zaloga, Steven J., Jim Kinnear, and Peter Sarson (1995). KV-1 & 2 Heavy Tanks 1939–1945. Oxford: Osprey Publishing. ISBN 1-85532-496-2