IS-2 tank

The IS-2 (Russian: Joseph Stalin) was a Soviet heavy tank of the Soviet-German war. IS is the official name of the serial Soviet heavy tanks produced between 1943 and 1953. The index 2 indicates the second production model of this tank family. During the Soviet-German war, the name IS-122 was used along with the designation IS-2 on an equal footing, in which case the index 122 denotes the caliber of the main armament of the vehicle. The IS-2 was the most powerful and heavily armored of the Soviet production tanks of the war period, and one of the strongest tanks in the world at the time. Tanks of this type played a significant role in the battles of 1944-1945, especially distinguishing themselves in the assault on cities. After the war, the IS-2 was modernized and was in service with the Soviet and Russian armies until 1995. IS-2 tanks were also supplied to some countries and participated in several post-war armed conflicts.

The first version of the IS-2 heavy tank with an 85-mm D-5T gun (Object 237) was developed in the summer of 1943 at the Chelyabinsk (Kirov) Plant under the leadership of the lead designer N.F. Shashmurin. On August 7, the tank was put into service by a decree of the State Defence Committee. The newly created 122-mm D-25T tank gun (which initially had a piston breech) with an initial projectile velocity of 781 m/s could hit all major types of German tanks at all battle ranges.

After producing 3,483 tanks in mid-1945, production was discontinued.

The IS-2 tanks were put into service with separate heavy tank regiments, which were already designated “Guards” when they were formed. At the beginning of 1945, several separate Guards heavy tank brigades were formed, each with three heavy tank regiments.

The IS-2 heavy tank was derived from the KV-1 tanks. N. Tseits, who had just been released from prison, was appointed as the project's lead designer. Later, N. Shashmurin was appointed. The design team also included K.I. Kuzmin (hull), N. Sinev (turret), S. Mickiewicz (chassis), and G.N. Moskvin (general layout). The KV-13 was created as part of the idea of a universal tank that corresponded to a medium tank in terms of weight and a heavy tank in terms of protection. The project featured extensive use of armor casting. Not only the turret, but also the main elements of the hull - the nose, the under-turret box, and the hull stern block – were cast. This made it possible to reduce internal unused volumes, differentiate armor protection, and ultimately reduce the number of armor plates.

The most immediate impact on the pace of production of these vehicles was the appearance of new German heavy tanks “Tiger” on the Soviet-German front in the fall and winter of 1942-1943. Decree No. 2943ss of February 24, 1943, ordered the Chelyabinsk Kirov Plant and Plant No. 100 of the (as the Experimental Tank Plant had become known by that time) to manufacture and submit for state testing two prototypes of the Joseph Stalin IS tanks. The first one, armed with a 76-mm ZIS-5 gun, was designated IS-1, retaining the factory index “Object 233,” and the second, with a 122-mm U-11 tank howitzer in a turret borrowed from the KV-9 experimental heavy tank, was designated IS-2 (Object 234).

The tests of both machines took place from March 22 to April 19, 1943 and were generally successful. The commission recognized that due to a denser layout than in the KV-1s, the IS tanks have stronger armor and higher speed at equivalent armament in the IS-1 and more powerful in the IS-2, despite having a smaller weight. However, significant defects were noted, mainly in the powertrain and suspension. On soft ground, the tanks encountered significant resistance due to the sagging of the track links into the intertrack space, which was greater than in the KV-1s. The commission recommended increasing the number of support rollers on the next IS models.

In parallel with the tests at the CTP, preparations for the serial production of new combat vehicles were in full swing at Plant No. 100 and the main related enterprises – ukrainian tractor plant and Plant No. 200. But subsequent events forced very serious adjustments to be made. In early April, reliable data on the armor protection of the Tiger was obtained, and on April 15, the State Planning and Control Committee issued Decree No. 3187ss, which obliged the People's Commissariat of Armaments to create powerful tank guns capable of fighting new enemy vehicles.

At the end of April, the sole trophy "Tiger" was shot with various artillery systems at the Bogdan Trubchaninov Scientific Research Institute's range in Kubinka near Moscow. It was found that the most effective means of combating it was the 85mm anti-aircraft gun model 52-K from 1939, which pierced its 100mm armor from a distance of up to 1000m. Decree No. 3289cc of May 5, 1943, "On Strengthening the Artillery Armament of Tanks and Self-Propelled Units," instructed the design bureaus to focus on the ballistics of this gun. In accordance with this decree, the Central Artillery Design Bureau - TsAKB (headed by V.G. Graben) and KB of Plant No. 9 (Chief Designer F.F. Petrov) proposed to develop and install 85mm guns with the ballistics of the 52-K anti-aircraft gun on two KV-1s tanks and two experimental IS tanks.

In the first half of June, four guns-two S-31s from the Central Design Bureau and two D-5Ts from Plant No. 9-were ready. The S-31 was designed with an 85-mm barrel on the cradle of the 76-mm ZIS-5 serial tank gun, which could have made its production much easier. The D-5T was a variant of the D-5S gun developed for the SU-85 self-propelled artillery unit, and was characterized by its low weight and short rollback distance.

During the preliminary design of the IS tank layout with an 85-mm gun, it turned out that with an internal diameter of the turret shoulder of 1535 mm, it was impossible to install such a gun without a sharp deterioration in the working conditions of the crew. Therefore, it was decided to extend the shoulder to 1800 mm, increasing the volume of the combat compartment and, accordingly, the length of the tank by 420 mm. As the length of the hull between the second and third support rollers increased significantly, a sixth support roller (on each side) had to be added to the tank's chassis. A new turret was cast at Plant No. 200 to fit the increased diameter of the shoulder. All these changes increased the weight of the tank to 44 tons, reduced its specific power and worsened its dynamic characteristics. The tank with the 85-mm gun was designated Object 237. Two prototype ISs, No. 1 with the S-31 gun and No. 2 with the D-5T gun, were ready in early July 1943.

Simultaneously with the work on Object 237, the CTP produced two preliminary designs for the installation of an 85-mm gun on the KB-1s tank. The first version, Object 238, was a production KB-1s with a S-31 gun in the standard turret, while the second, Object 239, received a turret from Object 237 with a D-5T gun.

In July 1943, comparative tests of all four tanks were conducted. Based on the results, the D-5T gun and Objects 237 and 239, which have since been called the IS-85 and KV-85, respectively, were preferred. Due to the small combat compartment and the inability of the crew to work normally in it, Object 238 was rejected.

On July 31, the KV-85 and IS-85 tanks arrived at the Kubinka testing ground of the Bogdan Trubchaninov Scientific Research Institute to undergo state tests. The equipment was accompanied by 28 specialists led by the chief engineer of Plant No. 100, N.M. Sinev. The tests began on August 2 and were carried out by a commission headed by the chief of the Technical Department of the Red Army's Main Artillery Directorate, Major General S.A. Afonin. Artillery tests were conducted at the Gorokhovets artillery range. Based on the results, the commission recommended that both models be accepted for service. The tanks were then placed at the Cherkizovo station in the workshops of evacuated Plant No. 37. On August 8, a column of experimental combat vehicles passed through the streets of Moscow to the Kremlin, where they were reviewed by Stalin, Molotov, Voroshilov, Beria, Fedorenko, Malyshev, and others. Before the demonstration, all members of the crews (except for the mechanics-drivers) were removed and replaced by the People's Commissariat for Internal Affairs personnel.

On September 4, 1943, by the order of the State Defense Committee No. 4043ss, the heavy tank IS-85 was accepted into service by the Red Army. The same order obligated Experimental Factory No. 100 to design, manufacture, and test, in collaboration with the Technical Department of the State Committee of Defense, a tank IS armed with a 122 mm gun by October 15, 1943, and by November 1, an artillery self-propelled gun based on it, the ISU-152.

Contrary to the widely circulated version in literature, during the aforementioned demonstration to Stalin, the tank IS-2 with a 122 mm gun and the self-propelled gun ISU-152 were not shown. It is possible that the authors mistook the IS-2 for the IS No. 2 (i.e., armed with the D-5T gun) and the self-propelled gun SU-152 (KV-14), but with an improved ventilation system for the fighting compartment.

The State Commission developed proposals to improve the design of the IS tank, some of which were clearly influenced by foreign experience. The latter include proposals to design and test a hydraulic mechanism for rotating the turret and turret mounted anti-aircraft machine gun on the hatch of the command turret, to develop a turret mounted 50 mm mortar for self-Defence and launching flares. It was also proposed to design a cradle suitable for mounting 85-, 100-, 122-, and 152-mm guns.

The idea to arm the IS with a gun of a larger caliber than 85 mm was first expressed by the director and chief designer of Plant No. 100, Kotin. In early August 1943, while studying the results of the Battle of Kursk, he noticed that of all the artillery systems, the 122-mm hull gun of the 1931/37 model (A-19) was the best at fighting the Tigers. The same conclusion was reached by the designers of Plant No. 9, where a prototype of the D-2 heavy anti-tank gun was developed and manufactured by fitting a barrel with the ballistics of the A-19 gun to the carriage of the 122-mm divisional howitzer M-30. This powerful gun was intended to be used primarily to combat enemy heavy tanks. Since the barrel of such a gun was mounted in the cradle and carriage of the M-30 and the D-2 gun successfully passed the test, the idea of installing the A-19 barrel in a heavy tank using a round cradle, anti-roll devices and a lifting mechanism from the experimental 122-mm tank howitzer U-11, as was done when creating the 85-mm D-5T and D-5S guns, became realistic. However, this was possible only if a muzzle brake was introduced into the gun design.

On November 12, the first sample of the "A-19 tank" gun was produced - the barrel of the D-2 gun, taken from the M-30 carriage, was installed in the D-5T gun mantlet, with additional machining of its guiding part to the diameter of the mantlet. The T-shaped muzzle brake was also borrowed from the D-2 gun.

The state trials of the IS-122 tank (Object 240) were carried out very quickly and generally successfully. After that, it was transported to one of the suburban proving grounds, where, in the presence of Voroshilov, a 122-mm shell was fired from a distance of 1500 m from the gun, hitting an already empty and shot-up German tank Panther. The shell pierced the side armor of the turret turned to the right, hit the opposite plate, tearing it off along the welded joint and throwing it several meters away. During the trial, the T-shaped muzzle brake of the A-19 gun exploded, and Voroshilov narrowly escaped death. After this, the muzzle brake was replaced with another one - a two-chambered one of German design.

The first production IS-85 tanks were manufactured in October 1943, and the IS-122 in December. In parallel with the assembly of ISs, production of KV-85 tanks continued at CTP until the end of the year. In January 1944, the last 40 IS-85s left the CTP shops, after which the plant began to produce increasing volumes of IS-122s equipped with the new 122-mm D-25T gun with a wedge-shaped semi-automatic bolt, which slightly increased the rate of fire (from 1-1.5 to 1.5-2 rounds per minute). In March 1944, the German-style muzzle brake was replaced by a more efficient one designed by the Central Design Bureau. At the same time, the IS-85 tanks were renamed the IS-1, and the IS-122 was renamed the IS-2.

The low rate of fire and small ammunition capacity of the new heavy tank were not satisfactory for the military - it only had 28 separate loading rounds. For comparison, the IS-1 had a ammunition capacity of 59 rounds, and the KV-1s had 114. Furthermore, after the first encounters between the IS-2 and the enemy's heavy tanks, it became clear that the standard 122mm armor-piercing round, BR-471, could only penetrate the frontal armor of the Panther from a distance of 600-700m. The weaker frontal armor of the Tiger could be penetrated from a distance of 1200m, but hitting a German tank from such a distance was only possible with well-trained experienced gunners. When using the powerful high-explosive fragmentation shell, OF-471, the welded seams of the IS-2 were cracking and even the frontal plate was tearing off at the welded seam. The initial results of their combat use were confirmed by firing tests of the tank at the Kubinka proving ground in January 1944 and prompted the designers to seek new solutions.

On December 27, 1943, Decree No. 4851 of the State Defense Committee was issued regarding the armament of the IS tank with high-power guns, and from February 1944, the design of three new tanks began - the IS-3, IS-4, and IS-5 (not to be confused with the post-war tanks of the same names).

Translation: In February 1944, the Central Design Bureau No. 48 was tasked with a research project on the topic "Study of the armor resistance of the hull of the heavy tank IS." The completed work showed that with the current shape of the front part of the hull, it would not be penetrated by German 75mm and 88mm shells only with the use of armor thickness of not less than 145-150mm (that is, 20-30mm more than the standard).

Based on the recommendations of the Central Design Bureau No. 48, changes were made to the hardening process and the design of the front part of the hull. The new hull with a so-called "straightened" nose retains the former thickness of armor. The driver's mechanic hatch, which significantly reduced its strength, was removed from the frontal plate. The plate itself was positioned at an angle of 60° to the vertical, which ensured its non-penetration even with direct fire from the German 88mm tank gun KwK 36 at course angles of ±30°. The lower frontal plate remained vulnerable, with an inclination angle of 30° to the vertical. To give it a greater angle of inclination, it was necessary to significantly change the design of the control compartment. However, considering that the probability of hitting the lower frontal plate was lower than in other parts of the hull, it was decided not to touch it. To enhance the armor protection of the lower frontal plate, starting from July 15, 1944, spare track links were placed on it between the towing hooks. Uralmashzavod switched to producing armored hulls with a "straightened" welded nose in May 1944, while Plant No. 200 began producing the same hulls but with a cast nose from June 1944. Tanks with old and new hulls were produced in parallel for some time until the supply was fully exhausted. It was not possible to significantly strengthen the turret armor, as this would have required a significant change in the design, so it had to be abandoned.

During production, the appearance of the tank turret underwent significant changes. The turrets of the first series tanks produced in 1943 had a narrow gun port. After the installation of the D-25T gun, despite its barrel being the same as that of the D-5T, using a telescopic sight became very inconvenient. From May 1944, the production of turrets with an enlarged gun port began, which allowed the sight to be shifted to the left. The armor protection of the gun mantlet and the thickness of the lower part of the sides were also increased. The commander's cupola was moved to the left by 63 mm, the PT4-17 periscope sight was removed, and the MK-IV observation device was installed in its place. A large-caliber DShK machine gun mount (designed by P.P. Isakov) was added to the commander's cupola. The IS tank turret remained essentially unchanged until the end of the war.