IS2 TANK – Heavy Soviet Tank Beast (Object 240)

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IS2 (Object 240) – Soviet heavy tank during the Great Patriotic War, was the most powerful and most heavily armored tanks of the Soviet and allied tanks of the war period, and one of the strongest tanks in the world at that time.

The abbreviation IS stands for ” Joseph Stalin ” – the official name of the serial Soviet heavy tanks produced in 1943-1953; index 2 corresponds to the second production tank model of this family. During the Great Patriotic War, together with the designation IS-2, the name IS-122 was used on equal terms, in this case the index 122 means the caliber of the main armament of the vehicle. The Germans called him in their documents KV-00 (IS).

Tanks of this type played an important role in the battles of 1944-1945, especially distinguishing themselves during the assault on cities. After the end of the war, the IS-2s were modernized and were in service with the Soviet and later Russian armies until 1993. Also, IS-2 tanks were supplied to a number of countries and participated in some armed conflicts after 1945.

 

 

History

Heavy tanks IS-2, IS-85 (IS-1) and KV-85 trace their ancestry to the heavy tank KV-1 / KV-1S.

Prerequisites for creation

The IS-85 (IS-1) and KV-85 were put into service in September 1943, but at the end of 1943 it became clear that they had insufficient armament for a heavy tank. The experience of the combat use of the 85-mm D-5 cannon on the SU-85 self-propelled anti-tank artillery mount and experimental firing at captured German heavy tanks showed that the D-5T gun does not allow achieving a decisive superiority over the armament of German tanks, moreover, in terms of its armor penetration it is inferior to the German 88-mm tank guns and the 75-mm KwK 42 L / 70 cannon mounted on the Panther tank. 85-mm gun D-5T at a distance of 500-1000 m caliber armor-piercing projectile could pierce the forehead of the German heavy tank ” Tiger I ” only when hit close to a straight angle ; the upper frontal part of the “Panther” did not penetrate at all. This put the new Soviet heavy tank at a disadvantage against the background of the ever-increasing number of Panthers on the Soviet-German front.

Since the main use of heavy tanks was to break through heavily fortified enemy defenses saturated with long-distance fire and field fortifications, the high-explosive fragmentation effect of shells played just as (if not more) an important role as armor-piercing. 85-mm shells borrowed from the 52-K anti-aircraft gun did not have a high-explosive version at all (they were fragmentation shells); although when installing some types of fuses, they could be used as high-explosive, but their action was only slightly better than that of 76-mm ammunition. This fact was also checked by self-propelled artillery – to fight against bunkers and strong bunkers, Soviet commanders preferred SU-122, not SU-85. However, the tower and the design of mounting the gun from the IS tank had a significant reserve for the installation of more powerful artillery systems.

Choice of weapons

In September 1943 the famous Soviet artillery designer of FF Petrov sent a letter to the chief designer CHKZ and pilot plant number 100 J. J. Kotin about the possibility of installing in tanks IS artillery systems caliber 107, 122 and even 152 mm. Zh.Ya. Kotin chose the 122 mm A-19 cannon to enhance the armament of the IS tank. After agreeing on the technical details, he received consent from I. Stalin personally to install the A-19 cannon in the IS tank. In the design bureau of plant number 9 under the leadership of FF Petrov, the A-19 was modified for installation in a tank – it was equipped with a muzzle brake to mitigate significant recoil, with more compact recoil devices, moved the controls to one side for the convenience of the gunner in the cramped fighting compartment of the tank. This modified version of the A-19 was named D-25T, and its mass production was launched at Plant No. 9 immediately. At first, there were difficulties in mastering it, so the question of installing the A-19 cannon directly into the IS was being worked out. However, they managed to overcome them, and in the future, the installation of the A-19 in the tank was not required.

Testing

At experimental plant No. 100, the prototype of the D-25 cannon was installed on the former Object 237 No. 2, an experimental version of the IS-1 with the D-5T cannon. This experimental vehicle received the designation “Object 240”. In October – November, at the Chebarkul training ground, it was tested by running and shooting. Initially, the D-25 was equipped with a T-shaped muzzle brake, which exploded during test firing (some sources claim that Marshal K. Voroshilov, who was present at the tests, was almost killed in this case). Subsequently, a two-chamber muzzle brake of the German type was installed on the IS, and then Plant No. 9 developed its own design of a two-chamber muzzle brake, which was installed on production vehicles.

The IS-2 was adopted by the armored forces of the USSR in accordance with the GKO decree No. 4479 of October 31, 1943. After successful tests of the “Object 240”, an order was received to immediately launch it into serial production at ChKZ. In November 1943, the assembly of the first production vehicles began. The new modification of the tank received the IS-2 index (during the war years, the designation IS-122 was used on equal terms with it, the first samples were sometimes also referred to in parts as KV-122). Production lasted from December 1943 to June 1945th, several cars of this brand were also produced by the Leningrad Kirovsky plant (on the territory of the Kirovsky plant in Avtovo there is an IS-2 tank on a pedestal (47 Stachek Ave.), the tank was installed on a granite pedestal in 1952 year (architect S. R. Gutan); on the front side of the pedestal there is a bronze plaque with the text: “1941-1945. This heavy tank was installed here in memory of the glorious deeds of the tank builders of the Kirov plant” (architect N. G. Eismont, sculptor Yu.G. Kluge)).

The baptism of fire of the IS-2 was adopted in early 1944, and it was forced, interrupting the planned thorough training of crews for the new vehicle. The high combat qualities demonstrated in battle immediately led to an order to maximize production of the IS-2. At the same time, test work was interrupted, as a result of which a lot of unfinished vehicles were sent to the front, and their failures caused a large number of complaints from the troops. To ensure the quality of the serial IS-2 and improve them at the beginning of 1944, J. Ya. Kotin and a number of his employees were removed from design work on new machines in order to eliminate defects in the IS-2 design. Launching the car was difficult: for example, in April 1944, military acceptance reported that there was no significant improvement in the quality of the IS-2 tanks and self-propelled guns produced at ChKZ on its basis. However, in the summer of 1944, the work being done to improve the quality gave the first results – about a third of the produced tanks managed to pass acceptance on the first try, and from November 1944 the quality of the received tanks was officially recognized as satisfactory – Zh.Ya. Kotin was returned to the post of head of the ChKZ Design Bureau and experimental plant number 100. In the winter of 1944/1945. reports from the troops testified that the IS-2 trouble-free operation covered the guaranteed mileage of 1000 km. The well-functioning production mechanism for the production of the IS-2 led to the fact that the 1945 machines were considered quite reliable and undemanding in operation.

 

 

Strengthening the protection of the tank

In parallel with the work to increase the reliability, research was carried out to strengthen the armor protection of the IS-2. The first option, although it was the best in armor protection among all Soviet tanks, was relatively easily hit by the 88-mm tank and anti-tank guns of the Wehrmacht. The 75 mm long-barreled guns also posed a significant threat to him. After analyzing the defeat, the designers of ChKZ came to the conclusion that the strengthening of the armor protection of the tower is no longer possible without a radical alteration of the entire structure, which was impossible in the harsh conditions of mass production. The installation of the 122 mm cannon made the turret heavier and upset its balance – the center of mass did not lie on the axis of rotation.turret, which was designed and balanced for the 85 mm D-5 gun. Additional booking, in addition to the general weighting of the vehicle, would have made it impossible to manually turn the turret with any significant roll of the vehicle and required a much more powerful electric motor to drive the turn. Therefore, the tower was left unchanged.

The protection of the hull was significantly improved by replacing the “stepped” upper frontal part with a straightened one. There were times when the upper frontal part did not penetrate point-blank even from the most powerful 88-mm Pak 43 anti-tank gun. However, the lower frontal part was still vulnerable. The thickness of the frontal armor reached 120 mm, the side armor – 90 mm, but the frontal armor part of some of the tanks was cast, not rolled (the latter, with equal thickness, provides better protection against penetration).

Further work

 

Further work to improve the security of heavy tanks was carried out in parallel by two teams – engineers from ChKZ and experimental plant No. 100. Interestingly, the head of both design bureaus was Zh. Ya. Kotin. Each of the teams promoted their projects, but in 1945, under the IS-3 index, a combined version of the Object 703 went into production, which, in fact, was an IS-2 with radically revised armor protection, taking into account the experience of the Great Patriotic War.

 

Description of construction

 

 

Layout

The IS-2 was essentially a further improvement of the IS-1, which, in turn, was a deep modernization of the previous model of the KV-1 heavy tank. Compared to the IS-1, the armament was more than significantly strengthened, and on modifications arr. 1944 with a straightened frontal armor, the protection against enemy fire in the frontal sector was also increased. Like all other Soviet serial heavy and medium tanks of the time, the IS-2 had a classic layout. The armored hull was sequentially divided from bow to stern into a control compartment, a fighting compartment and an engine-transmission compartment. Driver mechanichoused in the control compartment, three other crew members had jobs in the fighting compartment, which united the middle part of the armored hull and the turret. There was also a gun, ammunition for it and part of the fuel tanks. The engine and transmission were installed at the rear of the vehicle.

Armored corps and turret

The armored hull of the tank (except for the frontal part of some of the vehicles) was welded from rolled armor plates 90, 60, 30 and 20 mm thick. The design of the frontal part varied depending on the modification of the machine:

• IS-2 mod. 1943 had a cast frontal part of a streamlined “stepped” shape, in different parts its thickness varied from 60 to 120 mm.
• IS-2 mod. 1944 to increase the resistance of the frontal armor to the projectile was equipped with an improved “straightened” design of this part. Instead of a streamlined stepped tip of a complex geometric shape, the IS-2 arr. 1944 was formed by two flat armor plates, the upper of which had the shape of a trapezoid tapering towards the top of the tank and an inclination to the normal of 60 °. Some of the IS-2 arr. 1944 of the year were equipped with a cast frontal part, the thickness of the armor of which reached 120 mm; starting from the second half of 1944, with the availability of rolled armor of high hardness, the frontal part began to be welded from 90-mm armor plate

The frontal part was connected to the rest of the details by welding. The streamlined tower was an armored casting of a complex geometric shape, its sides 90 mm thick were located at an angle to the vertical to increase the resistance of the projectile. The frontal part of the turret with an embrasure for the gun, formed by the intersection of four spheres, was cast separately and welded to the rest of the turret armored parts. The gun mask was a cylindrical segment of a bent rolled armor plate and had three holes – for a cannon, a coaxial machine gun and sight. The tower was installed on a shoulder strap with a diameter of 1800 mm in the armored roof of the fighting compartment and was fixed with grips to avoid stalling in the event of a strong roll or overturning of the tank. The surface of the “contact” of the lower shoulder strap of the turret and the upper shoulder strap of the armored hull was somewhat recessed into the roof of the fighting compartment, which excluded the turret from jamming during shelling. The shoulder strap of the tower was marked in thousandths for shooting from closed positions.

For convenience in the repair and maintenance of units of the engine-transmission group, the roof of the engine-transmission compartment was made removable, and the upper aft armor plate could be hinged.

The driver was located in the center in front of the tank’s armored hull. Compared to the KV-1S tank, the dense layout of the habitable space of the IS tank did not allow the fifth crew member to be placed in it – a radio operator gunner. His functions were distributed between the commander and the driver-mechanic : the first worked with a radio station, and the second led indirect fire from a course machine gun by pressing the trigger of the electric trigger on one of the control levers. The course machine gun itself was located to the right of the driver and was rigidly mounted in a special armored pipe, which was welded to the frontal armor of the tank. Subsequently, due to the low effectiveness of indirect fire and the weakening of the frontal booking, the course machine gun was completely abandoned. Three crew members were located in the turret: to the left of the gun were the workplaces of the gunner and tank commander, and to the right of the loader. The vehicle commander had a cast observation turret with a vertical armor thickness of up to 82 mm…. The entering and exiting of the crew were possible through hatches in the turret: a round double-leaf hatch for the commander’s cupola and a round single-leaf hatch for the loader. The hull also had a bottom hatch for emergency escape by the crew of the tank and a number of hatches, hatches and technological holes for loading ammunition, access to the necks of fuel tanks, and other components and assemblies of the vehicle.

To the tank’s hull was welded a number of details – Travel Stops balance beams and brackets torsion suspension.

 

 

Armor

As an assessment of the security of the IS-2, we can cite a somewhat emotional judgment from the monograph “Tanks IS” that the IS-2 was the only large-scale tank of the anti-Hitler coalition, whose armor provided some protection against the famous 88-mm cannons and long-barreled 75-mm guns.

In terms of armor protection, 53% of the total mass of the IS-2 was accounted for by armoring the hull and turret, while the PzKpfw VI Ausf H “Tiger I” had 46.3%, and the PzKpfw V “Panther” – 38. five %. Of the German tanks, only the PzKpfw VI Ausf B “Tiger II” had the best indicator (54.7%), but this was achieved at the cost of a significant increase in the mass of the entire vehicle as a whole, with all the ensuing consequences. Frontal reservation of IP-well 2 opposed German shells: the top item “stepped nose” made its way caliber armor-piercing projectiles 88 mm cannon KwK 36 from 1000-1200 m, the 75 mm gun KwK 42 – from 800-900 m, a 75 mm cannon Pak 40 – from 400 m. For 1944, this was already considered clearly insufficient, therefore, as a result of intensive work, the protection of the forehead of the IS-2 hull was greatly improved. The 75-mm armor-piercing and subcaliber shells did not penetrate the “straightened” upper frontal part; 88 mm (KwK 36 L / 56) armor for molded nose 120 mm thick – no past abutment for rolled 90 mm thick – punched with 450 m reach the vulnerability of the gun. Pak 43 at medium and long range combat and failed… However, it should be borne in mind that in order to achieve such a result, a cast nose must be of good quality, without looseness and voids, which was not always the case. The lower frontal part was pierced by a 75-mm projectile from a distance of 785 m, a cannon mask 100 mm thick was also penetrated by German 88-mm KwK 36 cannon shells from a distance of about 1000 m.

In 1945, at the Kubinka training ground, special tests were carried out by firing the IS-2 with a straightened upper frontal part from a captured German early modification of the Hornisse self-propelled guns, armed with a powerful 88-mm Panzerjägerkanone 8.8 cm Pak 43/1 L / 71 artillery system with a length barrel 71 caliber. As in the case of the 88-mm KwK 36 cannon, the upper frontal part of the IS-2 was never penetrated by a caliber armor-piercing projectile, but, as expected, the range of effective destruction of the less protected areas of the tank significantly increased compared to the KwK 36…

Armament

Cases and shells of the D-25T tank gun. From left to right: a sleeve of an armor-piercing round, a sleeve of a high-explosive round, an OF-471 high-explosive cannon grenade, a sharp-headed armor-piercing tracer projectile BR-471, a blunt-headed armor-piercing projectile with a ballistic tip BR-471B. All shells are shown from two sides

The main arms EC-2 was gun D-25T caliber of 122 mm. The gun was mounted on trunnions in the turret and was fully balanced. However, in general, the tower with the D-25T gun was not balanced: its center of masswas not located on the geometric axis of rotation, which made it difficult to rotate when the machine was rolling. This negative circumstance was a consequence of the fact that the tower was designed and balanced for the 85-mm D-5T cannon, which was the original version of the armament of the IS tanks. The installation of the D-25T gun with a much longer and more massive barrel violated the calculated mass distribution around the turret rotation axis. The D-25T gun had vertical aiming angles from −3 to + 20 °, with a fixed turret position it could aim in a small horizontal aiming sector (the so-called “jewelry” aiming). The shot was fired by means of an electric or manual mechanical trigger.

The ammunition load of the gun was 28 rounds of separate loading. Shells and propelling charges for them were placed in the turret and along both sides of the fighting compartment. Compared to the wide range of ammunition for the 122 mm A-19 gun, the ancestor of the D-25T cannon, the IS-2’s ammunition load was significantly less diverse. It consisted of:

• sharp-headed armor-piercing tracer projectile BR-471 weighing 25 kg (explosive mass (TNT) – 156 g).
• a blunt-headed armor-piercing projectile with a ballistic tip BR-471B weighing 25 kg (the mass of the explosive (A-IX-2) is? g); developed in 1944, but appeared in large numbers in the troops in the very final phase of the war – in the spring of 1945.
• high-explosive fragmentation gun grenade OF-471 weighing 25 kg (explosive mass – TNT or Ammotol  – 3 kg).

All types of shells were fired at a full charge of Zh-471, which gave them an initial velocity of 792-800 m / s.

On the IS-2 tank, three 7.62-mm DT machine guns were installed : a fixed course, coaxial with a gun and a stern in a ball mount at high tide at the rear of the turret. Ammunition for all diesel fuel was 2520 rounds in disks. These machine guns were mounted in such a way that, if necessary, they could be removed from the mounts and used outside the tank. Starting in January 1945, a large-caliber 12.7 mm anti-aircraft machine gun DShK with a K-8T collimator sight began to be installed on the IS-2. The DShK ammunition was 250 rounds in strips in a box attached to the machine gun. Also, for self-defense, the crew had several F-1 hand grenades and were sometimes supplied with a pistol for firing signal flares.

On October 14, 1944, Stalin signed GKO decree No. 6723ss “On the installation of DShK large-caliber anti-aircraft machine guns on self-propelled artillery mounts and IS tanks.” In November, the first 25 IS-2s received anti-aircraft mounts of the DShK heavy machine gun. In December 1944, the anti-aircraft gun was installed on the 125 IS-2, and from January 1945, more and more tanks of this type received it.

Firepower

 

 

The 122 mm tank gun was a modification of the 1931/1937 model corps gun. A-19, received the D-25T index, was the largest-caliber serial tank gun of the Second World War – its muzzle energy was 820 t · m, while the 88-mm KwK 43 cannon of the German heavy tank PzKpfw VI Ausf B “Tiger II “, it was equal to 520 t · m (the KwK 36 and KwK 42 guns of the heavy tank

The practical results of firing from the D-25T and A-19 cannons at the range at German captured tanks with a blunt-headed BR-471B projectile from a range of 1400 m showed the following results] (there are doubts about some of them – due to confusion in the ChKZ documents – which tank was fired on and at what distance):

• The PzKpfw IV Ausf H tank was penetrated through the front and rear armor plates.
• The PzKpfw V “Panther” tank, upon hitting the upper frontal part of the armored hull, received a hole 150 × 230 mm with a crack along the weld; when it hit the side of the tower, a hole of 130 × 130 mm was formed, the opposite side of the tower was also pierced and it was torn off along the weld. When the turret hit the forehead, a 180 × 240 mm hole was formed, the turret was torn off the shoulder strap and shifted 500 mm from the axis of rotation.
• The PzKpfw VI Ausf E “Tiger I” tank, when a 122-mm projectile hit an existing hole from an 85-mm projectile in the frontal armor plate, was left without 82-mm aft armor plate, torn out at the welded seams, the projectile went through all the internal equipment of the tank. Upon hitting the roof of the tower (thickness 40 mm, angle of inclination 80 ° to the normal), a dent with a crack from the ricocheting projectile remained; when it hit the forehead of the tower, a hole of 580 × 130 mm was formed, the tower itself was torn off the shoulder strap and shifted 540 mm from the axis of rotation.
• The JagdPz “Ferdinand” self-propelled gun did not penetrate the forehead – a 122-mm projectile pierced the first frontal 100-mm armor plate with the formation of a hole 120 × 150 mm, but reflected from the second, when it hit the wheelhouse, a 100 mm deep dent remained in the armor plate.

Satisfactory results of armor penetration were achieved only due to the large mass of the projectile, which ultimately greatly reduced the rate of fire of the gun and reduced the ammunition capacity of the tank, in comparison with the armed 85-mm IS-2 gun, by more than two times, to 28 shells.

In early November 1944, a captured PzKpfw VI Ausf B “Tiger II” heavy tank was fired on at the Kubinka training ground. A 122-mm sharp-headed projectile pierced the upper frontal part (at the joints of the armor plates) from 600 m, the own 88-mm Tiger II cannon KwK 43 coped with this armor barrier from 400 m, and the Panther’s 75-mm cannon pierced the Tiger II’s forehead »From 100 m.

The high power of the high – explosive 122-mm projectile made it possible to achieve positive results when firing at enemy armored targets. The destructive effect of a high-explosive projectile is enhanced when it hits at an angle, compared with damage along the normal. Thus, the OF-471 high-explosive fragmentation grenade, when installed on a high-explosive action when firing at the Tiger II in Kubinka, when hit, knocked out the transmission elements of the latter and tore the welded seams of the frontal part. The purely high-explosive effect of a 122-mm 25-kg projectile with 3 kg of ammotol was 3 times superior to a similar German 88-mm high-explosive fragmentation projectile weighing 9.5 kg with 1 kg of ammotol (The dependence of the mass of the projectile on the caliber is cubic, because the projectile has three dimensions, that is, the quotient of the calibers must be raised to the third power: 122 mm / 88 mm = 1.386; 1.386³ = 2.66 times more).

The biggest and unavoidable drawback of the D-25T gun was its low rate of fire in comparison with the guns of German tanks (75-mm and 88-mm), which could withstand the IS-2. This rate of fire was due to the large mass of the projectile and the difficult operating conditions of the only loader. The sequence of operations with the piston bolt was as follows: opening the bolt, lowering the tray, placing a 25 kg projectile in the tray, sending it “with a ringing” into the chamber with a rammer, preparing the sleeve, putting it in the chamber, closing the bolt. At the same time, one should take into account the fact that the loader performed most of these operations with his left hand. Wedge gateonly made the work of the loader easier and slightly raised the rate of fire, which in the best conditions did not exceed 3 rounds per minute ; in reality, this figure was much lower (which is true not only for the IS-2, but for all tanks in general), when tested in Kubinka while moving at a speed of 12 km / h, the combat rate of fire was 1.35 rounds per minute.

It should be understood that in the case of the IS-2 we are talking about the combat rate of fire, which is determined not so much by the loader’s ability to quickly load the projectile into the gun barrel, as by the crew’s ability to quickly detect the target and aim at it. Based on this, it becomes obvious that the combat rate of fire of the IS-2 and the German “Tiger” was not fundamentally different, and perhaps the IS-2 had an advantage due to better equipment with observation devices.

If we talk about the technical rate of fire, or the rate of fire at the test site, then according to the data published in 2006 on the tests of the IS-2 at the ANIOP test site, the IS-2 rate of fire reached 6 rounds per minute.

There is an opinion that the low rate of fire was associated with the separate loading of the D-25T gun, however, the results of testing the 122-mm D-25-44 gun using a unitary projectile at the test site do not confirm this.

Accuracy of combat of the 122-mm D-25T cannon was at least as good as foreign guns – the average deviation of a 122-mm armor-piercing projectile from the aiming point when firing from a standstill at a distance of 1 km was 170 mm vertically and 270 mm horizontally. Soviet tests of the 88 mm KwK 43 cannon under the same conditions gave a deviation of 200 mm vertically and 180 mm horizontally. The IS-2 demonstrated good results when firing on the move; during tests in Kubinka at a distance of 700 m, the IS-2 hit the Panther tank four times out of five and the PzKpfw III tank two out of three times.

The traverse speed of the IS-2 turret was 13-16 ° per second, that is, a full revolution of the turret required 22-28 seconds. The electric drive allowed the turret to be rotated with the engine off and the machine roll up to 15 °. The manual drive made it possible to rotate the tower with a roll of 8.3 ° with a force of 16 kgf. For comparison: German heavy tanks had a hydraulic or manual turret drive; the speed of the turret traverse by a hydraulic drive depended on the engine speed (that is, when the engine was not running, the hydraulic drive was useless), being in the range from 5 to 19 ° per second. Research reports on German heavy tanks in Kubinka state that the hydraulic drive is complex and cumbersome, and its control is inconvenient.

It can also be said that the powerful armament of the IS-2 indirectly increased its security, forcing enemy tanks and self-propelled guns to open fire on the IS-2 from longer distances compared to combat with any other Soviet tank.

An excerpt from the “Report of the Spacecraft Self-Propelled Artillery Directorate on the work during the Great Patriotic War” testifies::

… the installation of 122-mm cannons on IS tanks returned to our tanks their temporarily lost superiority over the enemy in the artillery armament of heavy tanks. In terms of the power of its shot, the 122-mm D-25 cannon left the 88-mm guns of German tanks far behind.

The combat actions of the IS tanks showed that 122-mm cannons are the most effective means of fighting against heavy and medium enemy tanks, providing penetration of their armor from a distance of 2500 m…

Excerpt from the “Report on the combat actions of the 71st OGvTTP from 14.07.44 to 31.08.44”  :

… The fire armament of the IS-122 tanks is the most powerful of all existing types of tanks. The 122-mm projectile has a high penetrating ability, which determines the quality of these tanks as the best weapon in the fight against heavy enemy tanks…

Engine

The IS-2 was equipped with a four-stroke V-shaped 12-cylinder V-2-IS diesel engine with a capacity of 520 hp. from. The engine was started by an inertial starter with manual and electric drives or compressed air from two tanks in the fighting compartment of the vehicle. The electric drive of the inertial starter was an auxiliary electric motor with a power of 0.88 kW… The V-2-IS diesel was equipped with an NK-1 high-pressure fuel pump with an RNK-1 all-mode regulator and a fuel supply corrector. To clean the air entering the engine, a Multicyclone filter was used. Also, heating devices were installed in the engine-transmission compartment to facilitate starting the engine in the cold season. They could also be used to heat the fighting compartment of the vehicle. The IS-2 had three fuel tanks, two of which were located in the fighting compartment and one in the engine compartment. The tank was also equipped with four external additional fuel tanks with a capacity of 360 liters, not associated with the engine fuel system.

Transmission

The IS-2 tank was equipped with a mechanical transmission, which included:

• multi-disc main clutch of dry friction ” steel according to ferodo”;
• a four- speed gearbox with a range multiplier (8 gears forward and 2 reverse; second reverse gear can only be obtained theoretically, it is absent in a real car);
• two onboard two-stage planetary swing mechanisms with a steel-on-steel dry-friction multi-disc locking clutch and band brakes ;
• two double row combined final drives.

All transmission control drives are mechanical. Compared to the previous model of the KV-85 heavy tank, the planetary swing mechanisms were the new transmission element. The use of this unit made it possible to raise the overall reliability of the transmission as a whole, which was just the most significant drawback of the chassis of the KV series tanks and vehicles based on it.

Chassis

The IS-2 has an individual torsion bar suspension for each of the 6 solid gable road wheels of small diameter (550 mm) on each side. Opposite each road roller, the travel stops of the suspension balancers were welded to the armored hull. Driving wheels with removable pinion gear rims were located at the rear, and the sloths were identical to the road wheels. The upper branch of the track was supported by three small one-piece support rollers on each side; these rollers were borrowed from the design of the KV-85 tank. Track tensioning mechanism – screw; each track consisted of 86 single-ridged tracks 650 mm wide.

Mobility

The IS-2 heavy tank was regarded by the representatives of the Red Army as quite satisfactory in terms of its mobility, although with a 520-horsepower diesel engine and a mass of 46 tons, its power-to-weight ratio was the lowest among Soviet large-scale medium and heavy tanks. The specific ground pressure was about 0.8 kg / cm², which is much lower than the indicators of German heavy and medium tanks. The maximum speed did not exceed 35 km / h, but this characteristic was not decisive for a heavy breakthrough tank, since the main tactical application was combat in the same formation with the infantry, and more mobile T-34s were intended for the development of a breakthrough…. In the case of weak or absent enemy resistance, the IS-2 could be used to a limited extent to deepen the breakthrough, but its mobility characteristics were not conducive to such use.

In comparison with German heavy tanks (according to the Soviet classification), the IS-2 occupies an intermediate position between the Panther and Tigers of both modifications. “Panther” with its 700-horsepower Maybach HL 230 enginehas the best power-to-weight ratio, maximum and average speeds. However, it should be borne in mind that the “Panther” was not a breakthrough tank and was intended for solving other combat missions, where speed and operational-tactical mobility were among the defining parameters. The 55-ton Tiger I had a power density comparable to the IS-2, and the 68-ton Tiger II was inferior to the IS-2 in this parameter. All three types of German tanks differed from the IS-2 in their higher specific ground pressure, which left a certain imprint on their tactical use. In particular, in order to save the expensive and difficult-to-repair material of the German heavy tank battalions, they were rarely used off-road (the engine and transmission were overloaded, the chance of a tank getting stuck increased), while the IS-2 was more adapted to off-road conditions.On the territory of Germany and Western Europe with a developed road network, this lack of German cars was practically insignificant. On the other hand, “ironing” the trenches of the “lunar surface” of the front edge for the “Tigers” was fraught with failure of the transmission, while the IS-2 was quite suitable for this purpose.

Electrical equipment

The electrical wiring in the IS-2 tank was single-wire, the armored hull of the vehicle served as the second wire. The sources of electricity (operating voltages 12 and 24 V) were a GT-4563A generator with a 1 kW RRA-24F relay-regulator and two series-connected 6-STE-128 rechargeable batteries with a total capacity of 128 Ah. Electricity consumers included:

• electric motor for turning the tower;
• exterior and interior lighting of the vehicle, illumination devices for sights and scales of measuring instruments;
• external sound signal and signaling circuit from the landing force to the vehicle crew;
• instrumentation (ammeter and voltmeter);
• electric triggering of a cannon and machine guns;
• communication equipment – radio station and tank intercom ;
• the electrician of the motor group – the electric motor of the inertial starter, the bobbins of spark plugs for the winter start of the engine, etc.

Surveillance equipment and sights

The commander’s hatch and the loader’s workplace were equipped with Mk IV periscopes to monitor the environment from inside the vehicle. The commander’s turret had six viewing slots with protective glass. Driver mechanic IS-2 mod. In 1943, in battle, he conducted observation through a viewing device with a triplex, which was protected by an armored flap. This observation device was installed in an armored plug hatch on the frontal armor plate along the longitudinal centerline of the vehicle. In a relaxed environment, this plug could be pushed forward, providing the driver with a more convenient direct view from his workplace. In a later modification with a straightened armor, the hatch-plug was abolished, and the driver watched the situation through a gap in the frontal armor plate, using a viewing device withglass block. The viewing slit and the device were protected from the outside by a flat armor cap welded to the tank hull.

For firing, the IS-2 was equipped with a TSh-17 breakable telescopic gun sight for direct fire. Early series vehicles were also equipped with a PT4-17 periscope sight, but later it was abolished, and another Mk IV device was installed in its place. This improved the view for the gunner, but the lack of a periscopic sight made it difficult for possible independent shooting from closed positions. To ensure the possibility of fire in the dark, the scales of the sights had an illumination device. The DT stern machine gun could be equipped with a PU sight from a sniper rifle with a threefold increase. The DShKT anti-aircraft machine gun was completed collimator sight K-8T.

Means of communication

IS-2M in the village of Shatki, Nizhny Novgorod region

Communication facilities included a 10R (or 10RK-26) radio station and a TPU-4-Bis intercom for 4 subscribers.

10P or 10RK radio stations were a set of a transmitter, a receiver and umformers (single-armature motor-generators) for their power supply, connected to the on-board 24 V electrical network.

10P was a simplex short-wave tube radio station operating in the frequency range from 3.75 to 6 MHz (respectively, wavelengths from 50 to 80 m). In the parking lot, the communication range in the telephone (voice) mode reached 20-25 km, while in motion it slightly decreased. A greater communication range could be obtained in telegraph mode, when information was transmitted by a telegraph key in Morse code or another discrete coding system. Frequency stabilization was carried out by a removable quartz resonator, there was no smooth frequency control. 10P allowed communication on two fixed frequencies; to change them, another quartz resonator of 15 pairs was used in the radio set.

The 10RK radio station was a technological improvement of the previous 10P model, it became simpler and cheaper to manufacture. This model now has the ability to smoothly select the operating frequency, the number of quartz resonators has been reduced to 16. The characteristics of the communication range have not undergone significant changes.

Tank intercom TPU-4-Bis made it possible to negotiate between tank crew members even in a very noisy environment and to connect a headset (headphones and laryngophones) to a radio station for external communication.

Modifications

In the popular literature, the IS-2 of wartime is usually divided into two modifications – the 1943 model (with a stepped upper frontal part) and the 1944 model (with a straightened upper frontal part); but the famous military historian Colonel IG Zheltov in his monograph “IS Tanks” distinguishes six versions of serial IS-2.

In the post-war period, the IS-2s were modernized with the replacement of the engine, the installation of night vision devices, and tracked propeller flaps. This version received the designation IS-2M.

IS-2 based machines

 

On the basis of the IS-2, since April 1944, the heavy tank destroyer ISU-122 was produced, armed with a 122-mm A-19C cannon (which is identical in ballistics to the D-25T, but has larger recoil devices and is not equipped with a muzzle brake). Since September of the same year, on the basis of the IS-2, in parallel with the ISU-122, a new version of the self-propelled gun with a long-barreled 122-mm gun, the ISU-122S, was launched into mass production. Its armament was a self-propelled version of the D-25S cannon, which had noticeable structural differences from the tank version of the D-25T.

An earlier ISU-152 self-propelled gun to be considered as a machine based on the IS-2 would be somewhat inappropriate, although their running gears were almost identical. The prototype ISU-152 “Object 241” was built in October 1943, when the IS-2 itself existed only at the prototype stage, and the chassis for both prototypes (almost entirely from the IS-2, to a lesser extent from the ISU-152) was borrowed from the previous model of the heavy tank IS-1 (IS-85).

 

The heavy tank IS-2SH (IS-M) is a design version of the deep modernization of the IS-2, proposed by Nikolai Shashmurin at plant number 100 in early 1944. The project provided for the aft location of the fighting compartment, as well as the installation of a 122-mm long-barreled gun.

In early December 1943, the Main Armored Directorate of the Red Army approved the tactical and technical requirements for a promising heavy tank. Curiously, the IS-2 was put into service at the end of October 1943, that is, a month later the military had ready requirements for the next generation of heavy tanks. They sounded as follows: armor of the forehead of the hull and turret (most likely it meant projectile resistance) – 200 mm, sides – 160 mm, stern – 120 mm, armament of a 122-mm cannon or 152-mm howitzer cannon, engine power – 800— 1000 l. sec., maximum speed 35 km / h, weight – 55 tons, crew – 5 people.

At the beginning of 1944, according to these requirements, a group of designers of plant No. 100 under the leadership of N.F. Shashmurin developed a preliminary design of the tank, which is sometimes called the IS-M, IS-2Sh, IS Shashmurin, etc.

The layout of this vehicle was unusual for the Soviet tank building school. The fighting compartment, tower and transmission were located in the rear of the tank, the engine compartment in the middle, and the control compartment in the front. The undercarriage used large diameter track rollers without support rollers. The transmission of torque from the engine to the transmission was carried out using a propeller shaft that passed under the floor of the fighting compartment. The location of the turret in the rear of the hull did not allow the long-barreled gun to bump into the ground and made it easier to maneuver the tank in narrow passages. Since, at the beginning of the summer of 1944, the design bureau of the plant launched the design of two variants of the IS-6 heavy tank (Objects 252 and 253), work on the IS-M was stopped.

Organizational and staff structure

 

 

The IS-2, like the KV-85 or IS-1, entered service with individual guards heavy tank breakthrough regiments. Each OGvTTP had 21 tanks consisting of 4 companies of 5 vehicles each plus the regiment commander’s tank. The regiment commander usually had the rank of colonel or lieutenant colonel, company commanders – the rank of captain or senior lieutenant. Tank commanders were usually lieutenants, and driver-mechanics were sergeants (often technicians – junior lieutenants). The rest of the crew members according to the staffing table were privates… Regiments usually had several unarmored support and support vehicles – trucks, jeeps or motorcycles, the number of personnel of the regiment in the state was 214 people.

Also, in addition to individual tank regiments, heavy tank brigades of three regiments were armed with heavy tanks IS-2 with a nominal strength of 65 IS-2.