Chapter Three

Heavy Tanks

The first heavy tanks in Red Army service were a small number of British-designed and built Mark V Heavy Tanks captured from the White Army during the Russian Civil War. These vehicles had a crew of eight men and weighed upwards of 64,960lb (29.47mt) depending on their armament. Maximum armour thickness on the vehicle’s front hull was 16mm.

In Red Army service the Mark V was referred to as the Rikardo, taken from the manufacturer of the gasoline engines that powered the vehicles. These vehicles would last in Red Army service throughout the 1920s. In the Russian language, heavy tank translates as Tyazholyj Tank.

Influenced by the multi-turreted British-designed and built Vickers A1E1 Independent heavy tank prototype which weighed 71,680lb (32.51mt) and had an eight-man crew, the Red Army began design studies for a heavy tank in 1930, which led to the fielding of the eleven-man, gasoline-engine-powered five-turreted T-35 heavy tank series. July of 1932 saw the completion of the first prototype T-35. Construction of the first batch of ten production vehicles would take place between 1933 and 1934.

Belonging to the Tank Museum, Bovington, England is this Mark V heavy tank of First World War vintage. A number of these British-designed and built tanks had been captured by the Red Army during the Russian Civil War and placed back into service against their former owners, the White Army. (Tank Museum)

On display at Kubinka is one of the surviving British-designed and built Mark V heavy tanks captured by the Red Army during the Russian Civil War. These vehicles were 26ft 5in (8.05m) long, 13ft 6in (4.11m) wide and had a height of 8ft 8in (2.64m). (Vladimir Yakubov)

The standard production version of the T-35 series did not enter service until 1935 with construction continuing until 1938. It was referred to as the T-35 Model 1935 and had a lengthened chassis with four bogie assemblies on either side of the vehicle’s hull. This was in contrast to the three bogie assemblies on either side of the first ten units of the T-35 Model 1932 series.

On top of the superstructure of the T-35 Model 1935 was a large 360-degree rotating flat-topped turret shared with the last production batch of T-28 medium tanks. It was armed with a modified 76.2mm main gun. This was in contrast to the rounded-top 76.2mm gun-armed turret installed on the first ten vehicles. The 76.2mm main gun originally mounted in the T-35 Model 1932 series was designated the PS-3 76.2mm tank gun Model 1927/32 and was a modified version of the towed 76.2mm Model 1927 Infantry Support Gun.

The Red Army drew its inspiration for its first locally-built post-Civil War heavy tank (designated the T-35 series) from a British-designed and built heavy tank named the ‘Independent’. The British tank had four machine-gun-armed sub-turrets arrayed around a taller central turret armed with a 47mm main gun as seen here. (Tank Museum)

In lieu of a coaxial 7.62mm machine gun, the 76.2mm turret on the T-35 series had a 7.62mm machine gun mounted in the right-hand side forward portion of the turret in a ball mount. The last few production units of the vehicle also had a 7.62mm machine gun fitted in a ball mount in the vehicle’s rear turret bustle.

The T-35 series featured four smaller sub-turrets (with limited traverse) arrayed around the four corners of the vehicle’s superstructure. Two of the smaller sub-turrets on the original T-35 series had been armed with 37mm tank guns, with the remaining two turrets armed only with a single 7.62mm machine gun.

With the introduction of the T-35 Model 1935, the 37mm guns were replaced by 45mm versions. The original 45mm guns were later replaced by an improved longer-barrelled 45mm tank gun. The two-man 45mm gun-armed turrets on the T-35 Model 1935 were based on the turret design of the BT-5 Fast Tank, without the turret bustle. The remaining two one-man 7.62mm machine-gun-armed turrets on the vehicle were copied from the small one-man turrets seen on the Red Army’s pre-war light amphibious tanks.

In this German army picture the thickness of the armour is marked on a captured Red Army T-35 Model 1935 heavy tank that has been up-armoured. The tall central turret on the vehicle was armed with a 76.2mm main gun, while two of the sub-turrets were armed with a 45mm gun and the other two with 7.62mm machine guns. (Patton Museum)

By 1936 another 76.2mm gun designated the KT-28 Model 1927/32 was installed in the T-35 series. Some thought was given to mounting another 76.2mm gun in the T-35 series, designated the 76.2mm L-10 L/26, since it had superior armour penetrating capabilities and had been mounted in the T-28 medium tank. However, since the T-35 series already had two 45mm gun-armed turrets dedicated to anti-tank purposes, the 76.2mm L-10 L/26 was not fitted.

Out of the sixty-one T-35 series tanks built, the last six constructed between 1938 and 1939 were modernized and referred to as the T-35 Model 1938 Heavy Tank. They can be identified by the replacement of the slab-sided turrets seen on the T-35 Model 1935 with newly-designed turrets featuring sloped sides. Armour thickness on the front of the vehicle’s turret was also increased with a maximum thickness of 70mm compared to the 30mm found on earlier production units of the vehicle. Vehicle weight on the T-35 Model 1938 is reported to have reached 121,000lb (55mt).

The Red Army did not deploy the T-35 series during the Russo-Finnish War. It seemed to have been generally reserved for use in pre-war parades in Moscow’s Red Square where its size and armament array no doubt impressed the assembled visitors. The Red Army’s inventory of T-35s would, however, see combat in the early months of the German invasion of the Soviet Union with most being lost to mechanical failure. A few lasted long enough to see use during the defence of Moscow between December 1941 and January 1942.

The T-35 Model 1935 shown here was the standard production version of the vehicle. There was an earlier version designated the T-35 Model 1932 that can be identified by the fact that it had only three bogie wheel assemblies on either side of the hull instead of the four seen here. (Patton Museum)

Seen here on display at Kubinka is a T-35 Model 1935 tank. The vehicle was 31ft 11in (9.73m) long and 10ft 6in (3.20m) wide with a height of 11ft 3in (3.43m). The operational range of the tank was 93 miles (150km), typical for gasoline-powered tanks of that time. (Vladimir Yakubov)

Development of a suitable replacement for the unsatisfactory T-35 series began in 1938 and involved two different design bureaus. One was headed by Zh. Ya. Kotin and the other by N. Barykov. The original Red Army requirements for this proposed new heavy tank mandated a total of five turrets. This was soon dropped to a three-turret requirement, and with Stalin’s last-minute input it went down to two turrets. The larger, uppermost turret with 360 degrees of traverse was to be armed with a 76.2mm gun and a coaxial 7.62mm machine gun, and the smaller bottom turret with more limited traverse was to be armed with a 45mm gun and a coaxial 7.62mm machine gun.

The Kotin-designed contender for the proposed new heavy tank weighed 121,253lb (55mt) and was designated the ‘SMK’, the abbreviation for Sergey Mironovich Kirov, an early and prominent Bolshevik leader who was assassinated in 1934. The Barykov design bureau’s vehicle weighed 129,920lb (65mt) and was called the T-100 or Sotka, the Russian slang word for ‘100’. It, like the Kotin-proposed heavy tank, would mount a 76.2mm gun in its upper turret and a 45mm gun in the lower turret, both being fitted with coaxial 7.62mm machine guns. The maximum armour thickness on the front of the SMK turret was 60mm and 70mm on the front of the T-100 turret.

The two-turret requirement for the new heavy tank troubled the Kotin design bureau who felt it was outdated for modern tanks. So they received permission from Stalin to design a heavy tank based on components from their two-turret tank, but featuring only a single turret. The single-turreted heavy tank was to be armed with a 76.2mm main gun. It was referred to as the ‘KV Tank’ in honour of Marshal of the Soviet Union Klimenti Voroshilov, who was then the People’s Commissar for Defence of the Soviet Union and Kotin’s father-in-law.

German soldiers are examining what appears to be an abandoned T-35 Model 1935 tank. Not known for their reliability, the majority of T-35 series tanks lost during the early stages of the German invasion of the Soviet Union fell out due to mechanical problems or lack of fuel. (Patton Museum)

When the three prototype heavy tanks were tested in 1939, it was clear to all that the single-turreted KV was clearly superior to the two-turreted vehicles. To verify the testing results, all three prototypes were sent to participate in the early stages of the Russo-Finnish War. Of the three vehicles that saw combat in Finland, it was the KV that proved to be the most reliable. An added plus was that its maximum armour thickness of 90mm on its turret front made it immune to all the enemy direct-fire weapons it encountered. This demonstration of its combat effectiveness resulted in the decision in December 1939 to approve the vehicle for production as the KV-1.

The original five-man KV-1 weighed 99,207lb (45mt) and used the same diesel-powered engine installed in the much lighter T-34. This meant the on-and off-road mobility of the vehicle was inferior to the T-34 it was intended to work alongside; a problem that eventually resulted in the vehicle being restricted to units made up of only KV-1s. The vehicle rode on a torsion bar suspension system. The biggest problem with the KV-1 was the fact that its mechanical reliability proved inferior to that of the T-34.

German soldiers pose next to an abandoned T-35 Model 1935 heavy tank. Obsolete by the time the Second World War began due to its thin armour protection of only 30mm maximum, there was obviously the inherent difficulty in successfully commanding in battle a vehicle with a crew of eleven men. (Patton Museum)

The first version of the KV-1 series was referred to as the KV-1 Model 1939. It was quickly superseded in production by the improved KV-1 Model 1940 armed with the longer-barrelled F-32 76.2mm main gun. The KV-1 series was also armed with three 7.62mm machine guns. One acted as the coaxial machine gun with another in the front hull. The third machine gun was fitted in a ball mount located in the rear of the vehicle’s turret.

An unfounded belief in the spring of 1941 that the German army was upgrading its tank main guns resulted in the KV-1 Model 1940 being fitted with 35mm-thick add-on armour plates bolted to its turret and hull. Later production units of the KV-1 came off the assembly lines with a more thickly-armoured turret that made the addition of add-on armour unnecessary.

The next tank in the KV-1 series was the KV-1 Model 1941. It was this version of the tank that received the F-34 76.2mm gun that had appeared on the T-34 Model 1941 in February 1941. When mounted on the KV-1 Model 1941, the F-34 76.2mm gun was designated the ZiS-5. The ZiS-5 76.2mm guns were merely an improved version of the F-32 76.2mm gun that had a longer barrel than the previous 76.2mm main gun mounted on the KV-1 series. It can be identified on the KV-1 series because the barrel projected a few inches over the front of the vehicle’s hull. Due to temporary shortages, some KV-1 Model 1941s received the F-34 76.2mm gun instead of the ZiS-5 76.2mm version.

In an effort to keep the T-35 series viable on future battlefields, the Red Army had the last six production units of the vehicle fitted with new turrets that featured sloped armour, as is seen in this picture. In this configuration the vehicle was designated the T-35 Model 1938. (Patton Museum)

Unhappiness with the T-35 heavy tank series led the Red Army to seek out a new heavy tank. One of the three prototype candidates submitted for consideration to the Red Army was the twin-turreted design shown here that was referred to as the T-100. (Patton Museum)

Despite their superior level of armour protection, the roughly 500 KV-1 series tanks assigned to the western districts of the Soviet Union in the summer of 1941 did not fare well against the invading German army with the exception of some isolated occasions. The ill-trained crews of the recently-arrived KV-1s were at a serious disadvantage when engaging the better-trained veteran tank crews of the German army. Part of the problem was the poorly-designed crew layout in the KV-1 series turret that had the vehicle commander double as the gun-loader. Adding to the problem was the fact that the KV-1 series vehicle commander did not have an overhead hatch which would have allowed him to monitor the tactical situation around his vehicle when in combat.

Kotin had given some thought to designing and building a brand-new heavy tank referred to as the Obiekt 222, which later became known as the KV-3. It would be the replacement for the flawed KV-1 series but retaining the same ZiS-5 76.2mm gun. The KV-3 was initially supposed to be armed with the 107mm ZiS-6 gun, but it was decided that it was too powerful since the Germans didn’t have anything that would stand up to the standard 76.2mm tank gun at that point in the war.

Pictured is the single SMK prototype, knocked out in Finland. Field testing conducted in 1940 during the ongoing Russo-Finnish War showed the SMK and another twin-turreted heavy tank prototype known as the T-100 were both ungainly and too complicated to be practical in service. (Patton Museum)

Plans had progressed far enough in early 1941 that it was intended for the 156,526-lb (71mt) KV-3 to replace the KV-1 series on the assembly lines beginning in August 1941. The German invasion of the Soviet Union quickly brought an abrupt halt to that plan. As much as some would have liked to have seen the KV-3 fielded, it was recognized that any interruption of the existing production lines would have jeopardized the ability of the Red Army to field enough tanks on the battlefield to make up for the terrible rate of attrition it was experiencing in combat. Only a single prototype of the KV-3 was ever built and it had a maximum armour protection of 100mm on its turret front. The KV-3 prototype hull fitted with a standard KV-1 turret was later committed to combat and eventually destroyed.

Some thought had been given to mounting a new turret on the KV-1 armed with a 107mm main gun. This design concept had been assigned the designation Obiekt 220 and would have included adding a new and more powerful engine in the KV-1 hull. Nothing ever came of the project as the Red Army was more interested in the quantity of tanks being built rather than the quality.

There were also plans to develop a couple of super-heavy tanks, designated the KV-4 and KV-5. The KV-4 was to be protected by a maximum armour thickness of 130mm and the KV-5 a maximum armour thickness of 180mm. Both proposed super-heavy tanks were to be armed with a 107mm main gun. The obvious problem with these vehicles would have been their weight, estimated in the case of the KV-5 to be around 370,372-lb (168mt). With the German army overrunning the factory where these impractical projects were being contemplated, work was suspended and never restarted.

The KV-1 Model 1941 was succeeded in service by the KV-1 Model 1942, which featured a more thickly-armoured turret. This armour upgrade came at a price as the powertrain of the KV-1 series had been troublesome since its inception and the additional armour only made the problem worse. In total about 3,800 units of the KV-1 series were built between 1939 and 1943. There was also a flame-thrower variant of the KV-1 series built in small numbers and designated the KV-8. It mounted a 45mm main gun in lieu of the standard 76.2mm main gun to make room for the turret-mounted flame-thrower gun.

Combat experience gained during the Russo-Finnish War had shown that the existing Red Army tanks lacked the firepower necessary to destroy the heavily reinforced Finnish army bunkers being encountered. At the prodding of a senior general of the Red Army commanding troops in Finland, a new heavy breakthrough tank was conceived. In the span of two weeks a plan was hatched to mount a newly-designed turret mounting an M-10 152mm howitzer on an unmodified KV-1 series chassis. A prototype of this stop-gap vehicle was ready for testing in January 1940.

Of the three heavy tank designs submitted to the Red Army for consideration in 1939, the only one that made the cut was a single-turreted version of the SMK that would become the KV-1 series. Pictured is a vehicle from the first production batch sometimes referred to as the KV-1 Model 1939 and armed with an L-11 76.2mm main gun in a welded turret. (Patton Museum)

A German soldier examines a knocked-out KV-1 Model 1940 armed with a new F-32 76.2mm main gun. It can be identified by the welded armoured collar around the rear portion of the barrel that attached to the cast gun shield and protected the weapon’s hydro-pneumatic recuperator. (Patton Museum)

The initial prototype and a small number of very early series production units of this new heavy breakthrough tank were referred to as the KV-2 Model 1939. They featured a fairly complex angled turret design. The follow-on production units had a simpler and quicker to build turret design and were designated the KV-2 Model 1940. Production of the KV-2 series, nicknamed the ‘Dreadnought’ by its crews, began in November 1940 and continued until October 1941 with 334 units completed. Besides its main gun, the KV-2 was armed with three 7.62mm machine guns with the KV-2 Model 1940. Maximum armour thickness on the front of the KV-2 turret was 110mm.

Compared to the typical KV-1 series tank that weighed in at roughly 94,000lb (43mt), the six-man KV-2 might weigh as much as 114,000lb (52mt). The added 20,000lb (9.1mt) overloaded a chassis that was already plagued by automotive design issues. This made the KV-2’s on-and off-road mobility inferior to the KV-1 series. The large, heavy and unbalanced turret on the KV-2 also caused problems in traversing it on anything other than level surfaces.

A KV-1 Model 1940 has been caught in the woods and hit, evident from the smoke coming out of the hull and turret of the vehicle. The tank carried an authorized allotment of 111 76.2mm main gun rounds stored between the turret and hull, with most stored in the hull. (Patton Museum)

Some KV-2s were based in the western military districts of the Soviet Union that took the initial invasion blows of the German army. On those occasions where the KV-2 series was encountered by advancing German army units in the summer of 1941, the vehicle’s thick armour provided it with immunity to almost every weapon in the German arsenal except the 88mm FlaK gun. Fortunately for the German army, the KV-2s were few and far between, with most being lost to mechanical failure or lack of fuel. A small number of KV-2s would survive long enough to see service during the fighting for Stalingrad, which lasted from August 1942 until February 1943.

Following the KV-1 Model 1942 off the production line was another version in the KV-1 series designated the KV-1S. The KV-1S design corrected some of the problems found in the earlier versions of the KV-1 series. Production of the KV-1S began in August 1942 and continued until April 1943 with 1,370 units completed. The suffix ‘S’ in the designation was the abbreviation for the Russian word skorostnoi, which means speedy. As in the entire KV-1 series, there was a coaxial 7.62mm machine gun and a ball mount for a 7.62mm machine gun in the rear of the vehicle’s turret.

To improve the on-and off-road performance of the KV-1S, the designers did the only thing possible and thinned out the armour on the vehicle’s turret and hull, trading protection for mobility. This brought the vehicle’s weight down to 93,695-lb (42.5mt). Maximum armour thickness on the front of the KV-1S turret was 82mm.

There were also powertrain improvements to the KV-1S, especially to the transmission, to improve the vehicle’s reliability. Another big improvement on the tank was freeing the vehicle commander from his secondary job as a loader and providing him with an overhead armoured cupola to improve his situational awareness on the battlefield.

German cavalrymen ride past a knocked-out KV-1 Model 1940 tank. Visible on the side of the turret are riveted add-on armour plates that began showing up in April 1940. This took place because of an unfounded belief that more powerful German anti-tank guns were being fielded. (Patton Museum)

A German officer poses next to a knocked-out KV-1 Model 1940 tank. The welded armoured turret is fitted with the riveted add-on armour plates. The vehicle was 22ft 2in (6.75m) long, 10ft 11in (3.33m) wide and 8ft 11in (2.72m) tall. (Patton Museum)

The KV-1S also featured a smaller, more streamlined turret than its predecessors. However, it still retained the 76.2mm ZiS-5 main gun of the earlier versions of the vehicle. This was not a popular decision with General M.E. Katukov, one of the best and brightest tank commanders of the Red Army. He correctly foretold in a meeting with Stalin in September 1942 that the German army would soon field a next generation of tanks that would be immune to the 76.2mm main guns on the KV-1 series as well as the T-34.

As soon as Katukov’s predication was verified in August 1942 by the appearance of the German Tiger E heavy tank, production of the KV-1S began tailing off. Only 452 units were built in 1943 before the entire KV-1 series was cancelled. There had been an attempt to mount the S-31 85mm main gun in the KV-1S, but the arrangement proved impractical as the turret was too small to fit the larger gun.

The need for a replacement for the KV-1 series had not been ignored by the Red Army. By the autumn of 1942 the KV-1 series was clearly seen by all as a failure in service. A number of design projects were in the works to come up with a new tank under the umbrella designation KV-13. It was intended that the KV-13 could replace both the T-34 and the KV-1 series. However, when the German army began fielding the next generation of up-armoured medium and heavy tanks between January and June 1943, the KV-13 was not far enough along in the developmental cycle to be rushed into production.

On display at the Armoured Vehicle Museum located in Parola, Finland is the sole surviving example of a KV-1E, captured by the Finnish army during the Second World War. The add-on armour plates were also affixed to the vehicle’s upper hull as seen here. (Andreas Kirchhoff)

It was a team of engineers working under the direction of Kotin who managed to save the day by coming up with a new heavy tank design based on the KV-1 series. A prototype was shown to Stalin in August 1943 and with his approval was ordered into production. The vehicle was originally referred to as the izd.237. The prefix ‘izd’ is the abbreviation for izdeliye in Russian and translated means ‘item’. Upon being approved for production, the izd.237 became the IS-85, the prefix ‘IS’ being the Russian abbreviation for Iosef Stalin.

The IS-85 sported a brand-new three-man turret design that did not burden the vehicle commander with any secondary duties and provided him with an overhead armoured cupola as first seen on the KV-1S. Armament of the IS-85 was the new D-5T 85mm main gun. The IS-85 retained the coaxial 7.62mm machine gun and the rear turret-mounted 7.62mm machine gun as seen on all of the KV-1 series tanks.

Pictured on display at the Central Armed Forces Museum located in Moscow, Russia is this KV-1 Model 1941 armed with a new 76.2mm main gun. Vehicles with this gun can be distinguished by its longer barrel and new design for the cast gun shield. This particular vehicle retains the turret from the Model 1940. (Vladimir Yakubov)

The powertrain in the IS-85 was an improved version of that on the KV-1 series, and the suspension system was also very similar. The biggest design departure for the IS-85 from the KV-1 series was the much better-shaped hull that offered superior ballistic protection. The hull design for the IS-85 came from design work done for the KV-13 and dispensed with the bow machine-gunner in the front hull, bringing the crew down to four men.

Because it would take time for the factories and foundries to tool-up for production of the IS-85, Stalin also gave his approval in August 1943 for the production of an interim heavy tank mounting the new IS-85 turret on a widened KV-1S hull. This stop-gap vehicle was designated the KV-85 and 130 units were built between September and November 1943. It was the last version of the KV-1 series to see combat. The turret front armour of the KV-85 was 160mm thick.

To make room for the larger main gun rounds in the 101,411-lb (46mt) KV-85, the bow machine-gunner in the front hull was again dispensed with, leaving a crew of only four men.

Visibility out of the KV-1 series with all the hatches closed for combat was extremely poor and no doubt contributed to the driver of the vehicle pictured winding up in a large ditch. The vehicle was 22ft 8in (6.91m) long, had a width of 10ft 11in (3.33m) and was 9ft 7in (2.92m) tall. (Patton Museum)

Curious German soldiers are pictured on top of a still-smouldering KV-1 tank. Besides a 76.2mm main gun, the vehicle was armed with three 7.62mm machine guns, one of which was fitted in a ball mount at the rear of the turret bustle as seen here. (Patton Museum)

Production of the IS-85 began at the end of 1943 and continued until early 1944 with 107 units completed. However, doubts about the ability of the 85mm main gun to effectively deal with the armour on the late-war German tanks led to the decision to look at a larger, more potent main gun on the vehicle.

The weapon chosen in November 1943 for a couple of different reasons was a 122mm artillery piece designated the A-19. Firstly, there was then a large supply of these guns and their ammunition available and secondly, the weapon had performed well when engaging German Panther medium tanks and Tiger E heavy tanks at the battle of Kursk in July 1943. It also proved possible to shoehorn the enormous weapon into the same gun mount used for the 85mm main gun on the IS-85. The modified A-19 122mm gun mounted in the IS-85 became the D-25T and was eventually fitted with a large double-baffle muzzle brake.

Successful testing of the D-25T 122mm gun mounted in the IS-85 turret in November 1943 led to a quick decision to place this combination into production. The vehicle was originally called the IS-122 but this was soon changed to the IS-2 Model 1944, at which point the IS-85 was rechristened the IS-1 Model 1943. Some IS-1s were later rearmed with the D-25T 122mm gun, thus becoming an IS-2.

Like the KV-1 series, the IS-2 had a coaxial 7.62mm machine gun with another 7.62mm machine gun in a ball mount in the rear of the vehicle’s turret. There was also a fixed forward-firing 7.62mm machine gun in the front hull operated by the driver with a remote control. A new addition to Red Army tanks of the Second World War was the mounting of a 12.7mm machine gun on the IS-2 vehicle commander’s cupola for use against aerial and ground targets.

Several KV-1 Model 1941 heavy tanks armed with the ZiS-5 76.2mm main gun are pictured in a wood line. They retain the M1940 turret. The KV-1 series tanks were all seriously compromised in service by engine and transmission problems that proved much more serious than those encountered with the T-34 series. (Bob Fleming)

Pictured is a knocked-out KV-1 Model 1941 with a new welded up-armoured turret that can be identified by the squared-off shape under the turret overhang. The original welded armoured turrets on the KV-1 series bent around the bottom of the turret overhang from a point mid-way on the lower turret. (Bob Fleming)

The initial 150 production units of the four-man IS-2 rolled off the factory floor in February 1944. They were not placed into front-line service with the T-34 series but organized into special élite units. These units were in reserve until there was a large offensive operation against the German army, in which case they would form the armoured spearhead of the initial assault wave. Maximum armour thickness on the front of the IS-2 turret was 160mm.

Despite its large size, the armour penetration potency of the 122mm main gun on the IS-2 was not much more than that of the 75mm main gun on the Panther medium tank. Obviously, when firing at a non-armoured target, the high-explosive round of the IS-2 was much more effective due to its size. The IS-2 was a fairly effective weapon on the Eastern Front during its time in service.

The biggest fault with the mounting of the 122mm main gun in the 101,411-lb (46mt) IS-2 was the size of its ammunition. As a complete round would have been too heavy for a single loader, it was made separate, with the projectile going into the weapon’s breech first, followed by the cartridge case containing the propellant. Combined with the cramped interior of the IS-2, this meant the vehicle could only carry twenty-eight main gun rounds. By way of comparison, the KV-1S carried 114 rounds of main gun ammunition and the IS-1 had a main gun ammunition load of fifty-nine rounds.

To speed up production, Soviet industry introduced a cast armour turret in 1942 as is seen here on a KV-1 Model 1941. Armour thickness on this new cast armour turret was equal to that of the welded armour turret version of the Model 1941. The turret frontal armour was 100mm thick and the turret sides 75mm thick. (Bob Fleming)

In spite of some design shortcomings, the IS-2 proved extremely popular with Red Army tankers and more were requested. This led to an improved version with a newly-designed front hull glacis that offered a superior level of ballistic protection due its sloped design in comparison to the stepped glacis on earlier IS-2s. Another improvement was the replacement of the main gun’s manually-operated screw-type breech with a semi-automatic breech block, which increased the gun’s rate of fire from roughly one round per minute up to two rounds per minute. There was also a new wider gun shield fitted. These improved vehicles were referred to as the IS-2 Model 1944. By the time production ended in 1945 a total of 3,854 units of the IS-2 series had been built.

Even while production of the IS-2 series continued, the Red Army sought out the next-generation heavy tank. The design benchmark set for the IS-2’s replacement was that the vehicle had to be able to resist fire on its front hull and turret from the armour-piercing projectiles fired by the 88mm KwK43 gun mounted on the German Tiger B heavy tank. The standard armour-piercing projectile fired from the KwK43 gun had a muzzle velocity of 3,280ft per second and could penetrate 132mm of armour sloped at 30 degrees at a range of 2,187yds.

To optimize the ability of the replacement for the IS-2 to resist penetration by high-velocity armour-piercing projectiles, the Russian designers had come up with a large, thickly-armoured and highly-sloped hemispherical turret. It was a far cry from the more slab-sided turret on the IS-2. Maximum armour thickness on the front of the turret of this new heavy tank was 230mm. The two thick, sharply-angled armour plates welded together at the front hull of the vehicle that formed the glacis had a maximum armour thickness of 120mm.

The driver of the KV-1 series tanks sat in the centre of the front hull slightly to the right with the radio operator/bow machine-gunner to his left. Pictured is a KV-1 Model 1941 with a cast armour turret that is on display at the Armoured Vehicle Museum located in Parola, Finland. (Andreas Kirchhoff)

The prototype of the IS-2’s replacement was shown to a senior commander of the Red Army’s armoured forces in December 1944 and met with his excited approval. With input coming from two different design bureaus it would be designated the Kirovets-1, with ten pilot vehicles ordered for testing by the following month. Eventually the vehicle would be designated the IS-3. The first examples rolled off the factory floor in late May 1945, too late to see combat in the Second World War. Production of the IS-3 would continue until the middle of 1946 with 2,311 vehicles eventually completed.

Despite the new hull and turret design, the powertrain for the IS-3 was only a slightly improved version of that in the IS-2. It would also retain the four-man crew layout of its predecessor, and the D-25T 122mm main gun with its separate loading main gun ammunition. Due to the highly-sloped turret design of the IS-3, there was no turret bustle where main gun projectiles could be stored as on the IS-2. The twenty-eight main gun projectiles were therefore stored along the inside of the turret walls.

Like the IS-2, the IS-3 had a coaxial 7.62mm machine gun. Not seen on the IS-3 was the relatively useless 7.62mm machine gun fitted in a ball mount at the rear of the vehicle turret, as was standard on the KV-1 and IS-2 series. As with the IS-2 series, there was a 12.7mm machine gun on the IS-3 vehicle commander’s cupola for use against aerial and ground targets.

From a Second World War British army document appears this line illustration listing the various parts and components of a KV-1 Model 1941 tank with a cast armoured turret. (Patton Museum)

The 110,972-lb (50mt) IS-3 was debuted at a victory parade held in Berlin, Germany on 7 September 1945, when fifty-two of them roared past the assembled visitors, much to the astonishment of the Western Allies who didn’t know the monsters existed. Such was the shock at seeing a vehicle with modern design features that it would influence decades of tank development by the NATO armies to counter its potential on some future battlefield. In reality, the IS-3 was far from the perfect tank. Due to the haste with which the vehicle had been rushed into production, it was besieged by a host of design problems, mostly automotive, that were never resolved, even in the post-war era.

Later production KV-1 Model 1941 tanks with welded up-armoured turrets can be identified from the rear by the angled, instead of rounded, rear hull upper decks. This feature is clearly evident on this knocked-out KV-1 Model 1941 tank with a welded turret that has been turned into overhead cover for a German soldier’s bunker. (Patton Museum)

Like the T-34 series, the KV-1 series tanks had their transmissions located behind their diesel engines as is evident in this overhead picture of a KV-1 Model 1941 with a cast turret. Notice the rounded rear hull upper deck that marked the early production units of the KV-1 Model 1941. (Patton Museum)

A factory overhauling KV-1 Model 1941 tanks with both cast and welded armoured turrets. Improved German anti-tank weapons forced the thickening of the armour on later production cast turret KV-1 Model 1941 tanks. These can be identified by the fairing at the bottom of the turret side walls and the angled rear hull upper deck. (Bob Fleming)

This picture shows the interior of a cast armoured turret from a KV-1 Model 1941 tank. The vehicle’s gunner position was on the left-hand side of the main gun and the vehicle’s commander/loader position on the right-hand side. (Patton Museum)

In this image of the rear turret bustle of a KV-1 Model 1941 tank can be seen the 7.62mm machine gun and the various drum magazine holders for the weapon. On either side of the rear turret interior can be seen storage racks for 76.2mm main gun rounds. (Patton Museum)

This picture was taken inside a KV-1 Model 1941 tank from under the breech ring of the vehicle’s 76.2mm main gun looking forward into the front hull. Visible is the driver’s periscope as well as his instrument panel. The dark-coloured metal conduit in the centre of the picture carries electrical cables to the turret. (Patton Museum)

A comparison photograph of a KV-1 Model 1941 with a cast armoured turret and a United States army M4A4 medium tank with a cast armoured turret. The M4A4 was 9ft (2.74m) tall. (Patton Museum)

A German army intelligence photograph of a captured flame-thrower version of the KV-1 Model 1940 tank referred to as the KV-8. To make room for the flame-thrower, the original 76.2mm main gun was replaced by a much smaller 45mm gun to provide the vehicle crew with a limited ability to defend themselves against tanks. (Patton Museum)

To destroy heavily-fortified bunkers, the Red Army decided it needed a heavy tank armed with a 152mm howitzer. The vehicle was designated the KV-2 and an early production unit is seen here. The first few production vehicles had the turret sides angled inward to the front of the turret as seen here. (Patton Museum)

On display at the Central Armed Forces Museum located in Moscow, Russia is this standard production version of the KV-2 with a much simplified slab-sided turret and new-style gun shield. The six-man vehicle was 12ft 11in (3.93m) tall. (Vladimir Yakubov)

Pictured is an abandoned KV-2 with its turret pointed over its rear hull. Due to the size of the main gun rounds it could only store thirty-six of them within the tank’s hull and turret, with the majority being stored on racks in the turret. (Patton Museum)

For removal or replacement of the 152mm howitzer and the loading of the massive main gun rounds in the KV-2 there was a large armoured door in the rear of the vehicle’s enormous turret as seen here. Also fitted to the rear of the KV-2 turret was a ball mount for a 7.62mm machine gun. (Patton Museum)

A German soldier poses with a high-explosive projectile from a knocked-out or abandoned KV-2. The tank’s 152mm howitzer high-explosive projectile travelled at 1,430ft per second, which in theory would penetrate 72mm of armour. There was also a special concrete-piercing projectile for pillbox destruction. (Patton Museum)

An object of curiosity to the German soldiers pictured is this knocked-out KV-2 that has taken numerous hits to its large turret. One of the hits penetrated the 152mm howitzer barrel. (Patton Museum)

Seen here on display at the Central Armed Forces Museum located in Moscow, Russia is a KV-1S. The vehicle was a much-improved and lighter version of the standard KV-1 series tank with a newly-designed turret but still retaining a 76.2mm main gun. The hull of this vehicle is a reconstruction. (Vladimir Yakubov)

To rectify the problem of the KV-1S tank being under-gunned, there was an attempt to mount an 85mm main gun in the turret. This arrangement did not prove practical as the turret of the KV-1S proved too small. That experimental prototype survived and is seen here at Kubinka. (Vladimir Yakubov)

With the failure of up-gunning the KV-1S tank with an 85mm main gun, it was decided as a stopgap measure to take a KV-1S hull and mount on it a turret originally intended for the IS-1 heavy tank. The new turret mounted an 85mm gun and the vehicle seen here was designated as the KV-85. (Patton Museum)

One of the key improvements of the KV-85 seen here was the rearrangement of the turret crew positions. The vehicle commander was absolved of the loader’s role and the rear hull machine-gunner was given that job. The vehicle was 28ft 2in (8.58m) long and 10ft 8in (3.25m) wide with a height of 9ft 6in (2.90m). (Bob Fleming)

The replacement for the KV-1S and the KV-85 heavy tanks was the IS-2 heavy tank armed with a 122mm main gun. A captured example is pictured here and marked by the Germans with the thickness of the armour. The IS-2 featured both a redesigned hull and turret with a host of powertrain improvements. (Tank Museum)

A German soldier is looking over a knocked-out early production IS-2 that has no doubt suffered from its on-board ammunition being detonated as the gun shield has been blown out of position. The vehicle features a very large double-baffle muzzle brake to retard recoil. (Patton Museum)

An early production IS-2 tank is seen here on display at the National War and Resistance Museum of the Netherlands at Overloon. An identifying feature of early production vehicles is the stepped glacis that it inherited from the experimental KV-13 ‘universal tank’ and narrow gun shield. (Frank Schulz)

The transmission access hatches are visible in this picture of the IS-2 on display at Overloon. The armour side plates were 90mm thick. The rear hull armour was 60mm thick. Visible is the ball mount for a 7.62mm machine gun in the rear turret bustle. The vehicle was 32ft 6in (9.90m) long, 10ft 2in (3.09m) wide and 8ft 11in (2.72m) tall. (Frank Schulz)

The vehicle commander’s cupola on an IS-2 is shown here. The crew of the vehicle consisted of only four men: vehicle commander, gunner, loader and driver. The radio operator/bow machine-gunner’s position was dispensed with. Instead there was a fixed, forward-firing 7.62mm machine gun in the right front hull. (Frank Schultz)

A Red Army officer briefs the crews of his late production IS-2 tanks at the end of the war in Europe. Due to the weight of the projectile and propellant, it was decided to make the 122mm main gun rounds for the IS-2 separate-loading, which restricted the rate of fire to only two or three rounds per minute. (Patton Museum)

Later production IS-2 tanks can be identified by the sloping front glacis and the wider gun shield and are sometimes referred to as the IS-2 Model 1944. This particular vehicle is on display at Kubinka. Due to the size of the 122mm main gun rounds there was only storage space inside the vehicle for twenty-eight of them. (Vladimir Yakubov)

On display somewhere in the former Soviet Union is this late production IS-2M tank modernized post-war as indicated by the storage compartments built into the right side of the upper hull sides. These do not appear on wartime vehicles. (Patton Museum)

On display at Kubinka is this modernized IS-2M tank. Post-war, the vehicles were rebuilt to store thirty-five main gun rounds and had a number of other improvements made. The Soviet Union would supply the IS-2M to Red China, Cuba and North Korea during the Cold War. (Vladimir Yakubov)

The replacement for the IS-2 tank was the IS-3 heavy tank developed during the Second World War. It is shown here in Berlin during a September 1945 victory parade. Its sleek, low-slung appearance and huge 122mm main gun shocked the Western Allies who had nothing that could confront it on equal terms. (Patton Museum)

At Kubinka during an open-house event is this IS-3 tank modernized during the post-war era into the IS-3M. The IS-3 did not see combat during the Second World War with the Red Army. However, during the Hungarian uprising in 1956 the Soviet Army employed a small number of IS-3Ms against the anti-communist revolutionaries. (R. Bazalevsky)

A number of Egyptian army IS-3M tanks were captured by the Israeli army during the 1967 Six-Day War. The IS-3 and IS-3M were 35ft 3in (10.74m) long and 11ft 3in (3.43m) wide with a vehicle height of 9ft 6in (2.90m). (Israeli Embassy)

Belonging to the collection of the United States Army Ordnance Museum is this IS-3M tank. The contraption on top of the vehicle’s turret was the frame to mount a 12.7mm machine gun – not seen here – that could be employed against both aerial and ground targets. (Michael Green)

Looking down into the turret of an IS-3M tank can be seen the massive breech ring of the vehicle’s 122mm main gun. On the left-hand side of the image is the vehicle commander’s seat. The small handle to the left of this is the turret lock. (Chris Hughes)

The gunner’s position on an IS-3M is seen in this picture. The black handle to the left is the gunner’s manual traverse for the main gun. The smaller dark-green handle at the bottom centre of the image is the gunner’s manual elevation control for the main gun. (Chris Hughes)

Taken from the top of an IS-3M turret looking towards the rear you can see the storage racks for the 122mm projectiles. The propellant was kept in the lower hull. In the centre of the picture is an electrically-operated ventilating blower. (Chris Hughes)

This photograph shows the driver’s position on an IS-3M tank with his overhead hatch in the open position. Visible is the driver’s very simple instrument panel as well as his steering levers on either side of his seat. To his right is the gear-shift lever. (Chris Hughes)

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