IS-4 (Object 701)

Soviet Union (1946-Early 1970s)
Heavy Tank – 224 IS-4 and 25 IS-4M Built

Development of the IS-4 began as early as 1943 at the ChKZ plant in Chelyabinsk. After the complicated and convoluted development of the first series of prototypes under index Object 701, the project was abandoned. However, in 1946, the project was revived due to issues with the IS-3. Redesigned and equipped with the 122 mm D-25T gun, the tank would enter production in late 1946. Due to major production and reliability issues, it would not enter service until 1947. Even so, the entire service history was plagued by poor reliability. A mid-life upgrade was made in the 1950s, but the tank would see limited service, and, eventually, in the late 1960s, most found their dishonorable end as stationary guns along the Soviet-Chinese border.

Development

The IS-4 project can be traced back to summer 1943, when the ChKZ (Chelyabinsk Kirov Plant) began development of an IS-2 replacement out of its own initiative and funding. The IS-2 had not even entered service by this point, but several shortcomings regarding the IS-1 were well known and would pass on to its successor, with the main concern being armor protection. In November, the GABTU (Main Directorate of Armored Forces), recognising the need of a deep IS-2 modernization and even a replacement, laid down the requirements for a new heavy tank. Both the LKZ and ChKZ plants would begin development of independent and rivaling projects. The LKZ worked together with Factory No.100 and developed the IS-6 (Object 252 and 253) as well as a series of other drawings and prototypes. On the other hand, ChKZ not only developed an IS-2 upgrade, but also began development of extensive redesigns and completely new heavy tanks, which evolved into the IS-3 and IS-4.

In November 1943, GABTU laid down the requirements for a new heavy tank, with a mass of 55 tonnes, crew of 5, armor of 160 to 200 mm, 800 to 1,000 hp engine, and armed with an 122 or 152 mm gun. By 10 December, the ChKZ would present its project to the People’s Commissar of Tank Industry, V. A. Malyshev, who approved the project and supplied funding from the state. This first draft was known as project K or K-1, which featured a lengthened hull, thicker armor with redesigned armor layout, as well as a new turret.

By January, the project was given index Object 701, with several modifications made to the original model. While the hull remained mostly unchanged, the turret was altered, with a redesigned front and gun mantlet, new turret roof and the removal of the machine gun port at the rear. The gun was the 122 mm S-34-II and the tank was to be powered by the 750 hp V-12 engine. On 8 April 1944, Stalin gave the go-ahead for the production of two prototypes and two ballistic hulls of the Object 701. The first prototype, numbered No.0, began production on 10 April and was ready for trials by the end of April.

The development of the Object 701 and later IS-4 was done by the SKB-2 design bureau at ChKZ. Chief designer was head of the SKB-2, N.L. Dukov, the Chief Engineer was C.N. Makhonin, and Senior Engineer was L.S. Troyanov, later replaced by M.F. Balzhi. Other engineers that worked on the tank were G.V. Kruchyonyh (turret), V.I. Torotko, B.N. Yakovlev (hull) and G.A. Klemets (hull). These were all very experienced designers who had worked on most of the Soviet Union’s heavy tanks and self-propelled guns.

Production of an additional two prototypes was requested and were given indexes No.1 and No.2 and were produced between May and June. Prototype No.1 had several elements removed for ease of production, such as the turret handles and featured the 122 mm S-34-II gun and a 50 mm S-11 mortar in the turret. Prototype No.2 used an 100 mm S-34-I gun and the alteration of several elements, such as an additional headlight. Prototype No.1 began factory trials under a GABTU commission on 27 June and No.2 on 8 July. After these trials were concluded by the end of July, the prototypes were dismantled and analyzed.

After these trials, several issues were found regarding the transmission and V-12 engine.

For ballistic testing, a fourth, partially stripped-down prototype No.3 was produced, which was never equipped with a gun or any other finer components. Alongside prototype No.2, the two tanks were fired at between 5 and 25 August at the Kubinka artillery polygon with a series of guns such as the German 88 mm PaK 43 and 75 KwK 42 gun found on the Panther. Several Soviet guns were also fired at the tanks as well, including the 57 mm ZiS-2, 76 mm ZiS-3, 122 mm D-25T, and 152 mm ML-20. It was noted that the tank had superior protection against incoming fire compared to the IS-2, but was still not immune to 75 and 88 mm German guns, especially the turret, which could be penetrated by these guns from angles greater than 30°.

A total of 12 points were given for improving the protection of the tank, ranging from increasing armor thickness over various areas to increasing the heat treatment of certain plates. On 11 August, order No.500 from the People’s Commissar of the Tank Industry (NKPT) issued that, by 1 October, the ChKZ plant was to rework and build new prototypes of the Object 701 taking into account the various improvement areas resulting from the ballistic trials.

In the meantime, by 8 September, prototype No.2 continued factory trials without the GABTU commission, having traveled 673 km, during which the planetary transmission was replaced twice, with various issues reported.

By 1 September, design for a new prototype No.4 began, taking into account the ballistic trial improvement points as well as the various issues found on the mechanical components during driving tests. Over 22 components were replaced and redesigned, as well as improving the clutch and gearbox. For this task, both prototypes No.1 and No.2 were disassembled and, by 17 September, prototype No.1 had received the newly designed components, including a new lower hull, final drive and cooling fans.

On 21 September, the ballistic improvements for the Object 701 were laid down. The 120 mm frontal armor plates would be thickened to 140 mm, the driver bulge would be made out of welded plates instead of cast due to better hardening capabilities, the turret armor would be thickened from 160 mm to 200 mm, the joint between the turret wall and commander cupola was to be improved and lastly, and the turret roof armor was to be thickened to 45 mm. In order to maintain a manageable weight, the rear armor was to be reduced, with the plates behind the final drive to be reduced to 140 mm and the deck plates reduced to 100 mm.

A week later, both prototypes No.1 and No.2 had or were in the process of being fitted with new equipment and components, as well as the production of the new prototype, taking into account the aforementioned armor changes. With these changes, prototype No.1 was renamed to prototype No.5. However on 3 October, due to several mechanical problems, defects and delays, the improved prototype No.1 was still not ready for trials. In fact, its trials would only begin on 25 October, having covered 190 km in three days. Several issues were noted once again, namely that the engine had issues starting, the radiator had water leaks and the clutch disengagement link failed.

During the same period, prototype No.2 had also been improved, with additional fuel tanks, a gearbox removal system, water heating system copied from the German Panther tank, new reverse brake system, improved oil pump, new oil filter, and various other minor improvements. Its index was also changed from prototype No.2 to No.6.

Work on prototype No.4 continued in parallel and it was built in November, featuring the new armor layout. The three prototypes were trialed once again in the latter half of November, with prototype No.5 driving 1,000 km, after which its engine was disassembled and assessed for wear and damage. Prototype No.6 drove 200 km with an average speed of 23.1 km/h. As for the new prototype No.4, the transmission broke down after 103 km and the tank was recovered in early December.

After conclusion of the driving trials by the end of November, prototypes No.5 and 6 were armed with the 122 mm S-34 and 122 mm D-25T guns respectively and sent to Kubinka for ballistic trials. For testing of prototype No.5, a commission was created on 15 December, headed by engineer-colonel A.I. Blagonravov. The vehicle arrived the next day and underwent trials between 17 December 1944 and 24 January 1945, having traveled 1,051 km, of which 405 were on asphalt, 623 on country roads, and 23 over special obstacles. It is noteworthy to point out that the tank was fully loaded with ammunition, spare parts, and tooling. It reached a top speed of 41.14 km/h and had a range of 140 km on road with internal fuel tanks and 257 km using the external tanks. Despite several defects regarding a few systems and a supercharger failure, subsequently causing an engine failure, the tank was generally praised by the factory and the state commission. Engineer-Colonel Blagonravov noted in the report that:

“The experimental heavy tank (Object) 701 is superior to both existing domestic and foreign heavy tanks in its combat and technical capabilities. The heavy tank 701 has strong armor protection, powerful armament, good maneuverability and sufficient reliability of its mechanisms and systems. Driving the tank is simple and easy. […] The tank is simple and convenient to maintain and does not require frequent tinkering. Based on the test results, the commission considers it is necessary to recommend the 701 tank for adoption by the Red Army.”

Further testing of prototype No.5 was done at Kubinka from 28 January to 29 March 1945, traveling 400 km, of which 122 km were at night, with the rest done during harsh winter conditions. An average speed of 12 to 14 km/h was achieved, partially due to the snow covering up the lenses of the periscopes, requiring stops every 4 to 6 km to clean them. A series of issues with the transmission were also found. Colonel Blagonravov, in charge of the commission overseeing the trials, noted that the tank was fit for mass production.

A lengthy report was given describing the lengthy development of the Object 701 as well as its strengths and features. Thus, the commission proposed that the ChKZ should begin production of 25 to 30 units in February, 50 units in April and 100 units in May 1945, as well as the beginning of development of self-propelled guns on the chassis. Based on this, commanders of the armored and mechanized forces of the Red Army, generals B. Korobkov and N. Biryukov, heavily advocated for the adoption of the tank into the Red Army. On the other hand Malyshev was against the adoption of the Object 701 into service, stating that the vehicle had not been tested enough and that starting production of a new heavy tank would lead to a decrease in overall tank production.

To convince Malyshev to allow the tank into production, ChKZ factory director I. Zaltsman, Chief Engineer S. Makhonin, Chief Designer N.L. Dukhov, Chief Motor Designer I. Trashutin, and Chief Technologist Hunt sent a document to Malyshev on 20 March, further stating its advantages over existing tanks. They stated that the Object 701 fully satisfied GABTU’s technical and combat requirements and should enter service, while also mentioning that it used a variety of modern and capable features, such as the 800 hp V-12 engine, and had high reliability and maneuverability (according to ChKZ officials). At the end of the letter, this segment was written:

“Vycheslav Aleksandrovich, for the construction and perfecting of the 701 tank according to your instructions, we and the factory workers invested a lot of work and all our love, knowledge and experience, and, despite the great challenges and difficulties, with your help we can give the Army a good new tank in the shortest time possible.

We hope, Vycheslav Aleksandrovich, for your personal participation and assistance in resolving the issue of accepting the 701 tank into service and we consider it worthy to begin production in May”

It was here when the parallel development of the Kirovets-1 at ChKZ started to show its threat. This new heavy tank entered development in the latter half of 1944, born from the IS-2’s upgrade programs. Due to several innovative features, it would enter production and service much faster than the Object 701, under the name IS-3 (Object 703).

To prove the feasibility of producing both tanks simultaneously, ChKZ officials stated that they could produce 25 Kirovets-1 tanks and 100 Object 701 tanks in a month. It was proposed that the Object 701 enter pilot production with 10 units to be produced between April and May 1945. A further 25 a month would be made until August, 50 until September, and 100 tanks by October. Note that the production of the IS-2 was to end in June.

However, considering the military and economic context of the time, Malyshev knew that the ChKZ plant was not capable of producing two different heavy tanks simultaneously. The Object 701 was a far more complex and expensive tank to produce compared to the IS-2 and IS-3 and ChKZ would have required an entirely new production line.

Malyshev’s opinion on the matter became even more clear when, on 22 February 1945, he sent a letter to L. P. Beria, Deputy Chairman of the State Defence Committee of the USSR, regarding the 701 tank. Firstly, he stated that its trials were done on easy terrain and roads and that the engine was only used at 50 to 55% of its full power, instead of the normal 70 to 75%. On top of that, he was of the opinion that the new transmission, cooling system, and engine were not sufficiently tested. These factors made him believe that there was no way to be sure if the tank was truly ready for service.

Secondly, he considered that the IS-3 was far lighter, had identical armament, and was arguably better armored, and, due to being heavily based on the IS-2, could be put in production much quicker and units be sent to the army, around summer 1945. In contrast, Malyshev believed that, setting aside all the mechanical issues, it would have taken 4 to 5 months to set up the Object 701’s production, and the earliest deliveries would be made in September 1945.

Lastly, he commented on what he believed was the course of action regarding the 701 tank. He suggested that the armor was to be reworked, using the same scheme as the IS-3, that a small pilot batch of 10 tanks was to be produced in May-June and tested extensively, and only by September to start offering the tank for mass-production and service.

Naturally, General Korobkov, who was a strong advocate for the tank, did not agree with Malyshev, countering in a letter to Chairman Beria that the trials were in fact normal or even more demanding on the new tank than usual and that the new mechanisms added seemed completely reliable. He concluded his letter stating that the 701 was the most advanced tank created, especially considering the T-44 and its own host of issues.

An understanding and agreement was finally made in March 1945, when a letter signed by Malyshev, Korobkov, Biryukov, and Zaltsman was sent to Beria, requesting that the Object 701 was to undergo further testing, especially in more difficult terrain, as well as allowing ChKZ plant to start preparation for its mass production. On the latter point, Beria decided to wait until further notice.

The new series of trials began on 6 April with prototype No.6, which covered 102 km that day in thick mud, with an average speed of 13.1 km/h in fourth gear. The usual mechanical issues were present, such as a clutch component disconnecting and the oil pressure gauge failure.

On 8 April 1945, a commission headed by P. Voroshilov arrived to oversee the trials of the prototype at ChKZ. By 19 April, the tank had covered 548 km. By the end of the trials on 21 April, Voroshilov noted that the mechanical components and systems were reliable enough for mass production. Based on the reports of the trials of prototypes No.5 and No.6, on 20 July 1945, it was concluded that the tanks were sufficiently reliable for service, while being the most capable Soviet tank in terms of characteristics. However, Malyshev was hellbent on not accepting the tank into service, claiming that the production of heavy tanks was already troubled and it could not be further disturbed by the organization of the production of a new tank. Nonetheless, Chairman Beria was requested to allow the adoption into service of the Object 701 and allow for production of 10 vehicles in August. To not decrease the production of crucial tanks, the Object 701 would gradually replace the ISU-122.

Chairman Beria would only answer to this request on 7 August, ordering Malyshev to hold a meeting with the other members of the GABTU and tackle the issue of producing the Object 701. However, it was rather obvious that, by that point, the war in Europe was already over. Factory worker hours were reduced back to 8 hours a day, 5 days a week. The entire tank industry had to be shifted back to their original locations, as well as shifting production to peacetime standards. To top it all, problems with the T-54 would consequently give Malyshev another excuse to further delay the Object 701. On 25 August, General Korobkov sent a letter to remind Chairman Beria about the issue and that Malyshev and the GABTU had kept on ignoring the Object 701.

It is understandable that Red Army officials would want the best vehicles for their units, however, the reluctance shown by the GABTU and state officials was also justifiable. The war was over, tank production had to be scaled back and restructured for peacetime construction. There was also the question of the IS-3, which not only fully occupied the ChKZ’s production lines, but also made the Object 701 completely redundant in the eyes of many. Nonetheless, the fate of the Object 701 project remained in a constant state of uncertainty throughout 1945.

The IS-6

ChKZ was not the only plant that was working on the GABTU’s new IS-2 heavy tank replacements/deep modernizations. Plant No.100 also began its own project, the Object 252 and 253, later known as the IS-6 in March-April 1944. Technically, the IS-6 was more advanced and refined than the IS-4, however, its armor was significantly thinner, and the factory trials were not any more lustrous compared to the IS-4, with in the case of the Object 252, 14 roadwheels had to be replaced and the Object 253, which was fitted with an electrical transmission, caught fire during trials. Ultimately, the IS-6 was dropped with the advanced development of the IS-4 and the promising Object 703 (IS-3), with Plant No.100 moving on to develop even more powerful heavy tanks, leading up to the Object 260, the IS-7.

Revival

However, by the beginning of 1946, the glamor of the IS-3 started to vanish, and complaints started to reach the ChKZ plant from the Red Army. Due to the complexity of fixing all the minor issues with the tanks already in service, as well as the long time required, on 14 February 1946, Zaltsman turned to the Ministry of Transport Machine-Building of the USSR (formerly People’s Commissariat of Tank Industry (NKPT)) and Military Council of Armored and Mechanized Forces of the Red Army, proposing once again to replace the production of the IS-3 with the Object 701. On 21 February, the Military Council’s report regarding tank production for the 1946-1955 period explicitly mentioned the proposal of producing the Object 701 at ChKZ from June 1946 to the Minister of Defence. These plans were approved on 27 April by GABTU, but not by the Ministry of Transport Machine-Building. Nevertheless, on 29 April 1946, the Object 701 was accepted into service within the Red Army, receiving the name “IS-4”. Starting in September 1946, the ChKZ plant was ordered to build 155 tanks by the end of the year, with 10 units in September, 25 in October, 50 in November, and 70 in December. By 1 May 1947, the goal was to reach a production schedule of 6 tanks per shift, with two 8 hour shifts a day, and 6 tanks a day. In the meantime, the IS-3 would be phased out of production in the beginning of 1946 (this latter point was later scratched out as production of 150 more IS-3 was ordered by summer 1946). Production of the IS-3 finally ended in July (only 25 IS-3s were produced that month) and the factory was ready for IS-4 mass production by September.

However, by this point, Soviet factories in the Urals and Far East were experiencing a “brain drain”. Many of the skilled engineers and workers in these plants were brought in during the war, and were now returning to their homes in western parts of the USSR. Many of them had previously worked at plants in these areas, such as the engineers from ChKZ which were now returning to LKZ in Leningrad, as it was being rebuilt and many of them were natives from Leningrad. Many other skilled workers moved to civilian jobs, as there was no longer a large need of tank production, but an immediate need of rebuilding the devastated country from the war.

This migration had a direct negative effect on the Soviet military industry, and the IS-4 was no exception. On 29 April 1946, the ChKZ was ordered to complete eleven changes to the IS-4 before it was deemed ready for production.

• Addition of a rotating commander’s cupola with rangefinder.
• Mechanized ammunition loading system.
• Electric drive for aiming the main gun vertically.
• Addition of hydraulic shock absorbers.
• Improving the 3-stage gearbox.
• Improving the driver’s port.
• Reducing the stiffness of the clutch.
• Enhancing the starting of the engine in low temperatures.
• Adding a hydraulic servo drive.

The Ministry of Transport Machine-Building ordered these changes on 31 April.

Along with LKZ, Plant No.225, Plant No.100, and VNII-48, the ChKZ plant researched new elements to add on and improve on the IS-4, such as replacing the main gun with another more potent cannon, the addition of an anti-aircraft 14.7 mm machine gun on the roof, creation of snow-tracks meant to reduce the ground pressure in snow, improving production techniques, especially the welding of thick armor plates, etc.

However, many of these changes would not end up being implemented. The proposal of mounting a new main gun was quickly dropped. The 14.7 mm anti-aircraft was never mounted either. There was no room (internally or externally) to mount hydraulic shock absorbers and finally, the turret was too cramped to fit an automated loading system.

Preparing for Production

When setting up the tank for production, over 80 changes had to be made, leading to extensive delays in the production. Other factors, such as heavy focus on civilian tractor production at ChKZ, further delayed the production of the IS-4, and production could not begin in September 1946, as initially required. To offset the difficulties faced by the ChKZ, the Council of Ministers signed a resolution which would decrease the number of IS-4s to be built to just 50 tanks in 1946, with 17 tanks in October, 13 in November, and 30 in December. However, this resolution could not be fulfilled either.

By the end of 1946, only six IS-4s were produced between November and December. Many of these were in “production” for many months, the first tank having entered production in May 1946 and was finished in November. The tanks were significantly changed from those produced and developed in 1944-1945, and were largely based on prototype No.6. These tanks were not built to the required standards and latest plans. Unsurprisingly, none of the 6 IS-4s produced in November/December 1946 were accepted into service due to the military finding over 100 issues with these tanks during their own trials. One of these production issues was the use of welded side hulls, as solid piece hulls were delivered by Plant No.200 only in mid-December.

On 20 December 1946, the Ministry of Transport Engineering and the Council of Mechanized and Armored Forces united on making several adjustments to the IS-4 ahead of mass production in 1947. They had agreed on 40 separate proposals and 461 requirements for improving the tank. ChKZ was also heavily involved in this adjustment, introducing 1,398 changes, of which 324 were design improvements, 636 were drawing/blueprint improvements, and 433 were manufacturing/labor improvements. Among the required proposals, 51 changes were made to the IS-4, including:

• Increased the size of the driver’s hatch.
• Preventing the turret shoulder strap from jamming.
• Strengthening the turret basket floor.
• Strengthening the brakes.
• Introduction of a new hatch for access to the fine particle filter.

On 9 April 1947, the Council of Ministers agreed that ChKZ was to begin serial production in 1947 and produce 200 IS-4 tanks. To test the new changes made to the IS-4, a day later, Malyshev, who was now Minister of Transport Machine Building, ordered the trials of two IS-4s built in November 1946 (serial numbers 611A5 and 611A3) at the ChKZ plant supervised by a ministry commission. The trials lasted from 15 April to 23 June, during which both tanks drove around 1,100 km and had issues with the new clutch, slipping of certain gears and failure of the hydraulic servo system, amongst others. Post trial reports revealed that certain elements were still not satisfactory, such as the driver’s port, radio equipment and fire-fighting equipment. The weight of the tanks was measured to be 59,290 kg. The tanks proved to not be particularly fast either, being limited by the engine and topping at 32 km/h on cobblestone roads and 16/25 km/h on (wet/dry) dirt roads. Fuel range was no better, with 60 km or 2 hours and 30 minutes of non-stop driving. On the plus side, the tanks could topple trees half a meter thick. The engines ran between 83 and 104 hours.

The conclusion of the trials was:

• The underpowered V-12 engine was not capable of reaching more than 1,600 rpm, bottlenecking the tank’s speed and maneuverability. Additionally, its cooling was not effective.
• The engine cooling fans were incredibly loud and could be heard from a whopping 7 to 8 km away.
• There were reliability issues with the transmission, gearbox, and final drive.
• Both internal and external sounds from the tank (fans, engine, etc) interfered with the radio.
• Internal turret fan was not capable of clearing out fumes when executing a rate of fire of above 2 rounds per minute, which led to a high carbon monoxide buildup.
• Poor driver’s visibility when buttoned up.

Between March and May 1947, another ballistic test was done on IS-4 serial number 3, after which it was concluded that frontally, the tank was immune to 128 mm shells with an impact velocity of around 800 m/s, including the driver’s port, however, the weldings still shattered or split. The turret was also impenetrable to 128 mm shells with 800 m/s impact velocity. Only the side of the hull, due to the thinner armor and its design could be penetrated or its welding points shattered. General Orlovsky, who was in charge of the commission, suggested 18 points for the improvement of protection and construction of the IS-4 after the trials. Of these, 14 were accepted by the Ministry of Transport Machine Building.

Between June and July, another round of trials of the IS-4 built during the second quarter of 1947 was done at ChKZ, this time with a joint commission from the Ministry of Transport Machine Building and the Command of Mechanized and Armored Forces, resulting in 111 or 112 (depending on source) different improvement suggestions. These suggestions included:

• Decreasing the wear and damage of the bearings and gears in the gearbox.
• Improving the wear resistance of the brake pads.
• Improving the performance of the planetary transmission.
• Improving the engine cooling system.
• Reducing the noise generated by the engine.

Most of these issues were hotfixed during following production runs, with one main change made on 31 July and a second major change on 8 October. These constant flow of production changes slowed down overall production. Another limiting factor was the low supply of hulls and turrets from Plant No.200, which by 10 December, only delivered 59 units.

Production

Due to the high amount of testing, suggestions and improvement required by the Ministry and Army, the production of the IS-4 was delayed and slowed down significantly. The summer 1947 IS-4 tank was essentially a new tank compared to that originally accepted into production over a year earlier. In ChKZ’s own production report’s words:

“The IS-4 was adopted into service by a resolution of the Council of Ministers dated 29 April 1946, after which the customer presented a number of requirements for the modernization of the vehicle, which caused serious reworking of its design.

In total, 461 requirements were presented in 1947 for which the plant removed 238 components and 740 parts and reintroduced 264 components and 946 parts in the tank. This design change required additional testing of the machine in prototype samples and also during the production of the pilot batch, drawings for production were approved on 8 October 19478. Until then, the plant did not have the ability to stockpile components and parts, which further delayed production.

The production of IS-4 tanks in 1947 was also dependent on the hulls from Plant No.200. By 12 October, 59 hulls were received from Plant No.200.

Based on the requirements presented by the customer and the Minister of Transport Machine Building, as well as our own initiative, individual components of the IS-4 were modernized, after which 2 prototypes were ready and handed over to the interdepartmental commission. The first 25 tanks were manufactured according to the batch design plans and on 10 August, serial production blueprints were approved.

Changing the design of the tank required a lot of work to refine the blueprints. A total of 1,398 changes were introduced, including 324 to upgrade the design, 433 to improve the manufacture and 636 to clarify the drawings and plans. As a result, a number of defects were eliminated, especially in the transmission units and the tank’s performance improved.”

Nonetheless, two tanks produced in November/December were finally accepted in April 1947 and another four in July. Production during 1947 was also limited, with 52 tanks entering service, of which only 46 were actually built in 1947. This was abysmally low compared to the original quota of 200 tanks.

To mass-produce the IS-4, the ChKZ plant had to make an entirely new assembly line. This process required the development of 4,328 technological processes, 2,228 apparatuses,, 103 metal production tooling, and 3,050 new tools and a variety of other equipment changes.

As early as 9 April 1947, the Council of Ministers of the USSR outlined the reasons for the poor production of the IS-4, stating that despite the fact that ChKZ did have the ability to achieve these numbers, the Ministry of Transport Machine Building was more concerned about the program in terms of national economy rather than actually producing the tank. Likewise, they blamed the involved factories of not dedicating the required man hours, equipment, and funding necessary to achieve the quota. This production issue had been raised to the Ministry of Transport Machine Building several times, but it failed to organize the plants and increase production.

In early January 1948, Commander of the Armored and Mechanized Forces Marshal S.I. Bogdanov sent a letter stating that the army would no longer accept deliveries of the IS-4, due to problems with the tank’s transmission. To this, ChKZ responded claiming that this was a random mishap, mostly due to poor bearings and unusual operation of the transmission’s brake control drives. After a few weeks of bureaucratic back and forth, on 3 February, Malyshev (who was now Deputy Chairman of the Council of Ministers of the USSR) convinced the military to accept the tank back into service, with a list of improvements required for the tank, requiring the removal of all issues found by 15 March.

Similarly, based on the previous reports and new complaints from Plant No.200 regarding issues with poor technical documentation of the armor size and thickness given by ChKZ, Plant No.200 stopped production. Consequently, on 25 March 1948, the new Minister of Transport Machine Building, I.I. Nosenko, held a meeting with Marshal Bogdanov, GABTU’s Head of Technical Department, Lt.Gen. V.V. Orlovsky, and deputy ministers Maksarev and Lebedev, where they would command the ChKZ to fix issues with the gearbox and planetary transmission. Additionally, Maksarev and Orlovsky were sent to assist ChKZ. Shortly after, on 29 March, the issues of thicknesses of components and armor were fixed by agreeing and reviewing the problems and Plant No.200 would resume work.

Throughout the production run of the IS-4, several improvements were made, such as in March 1948, the TPU-47 intercom was added, in May, the roadwheels were adjusted to not hit the return rollers, in August, when an automated fuel “dumping” system was added.

During spring/summer 1948, GABTU once again tested seven IS-4 tanks. All of them suffered engine, gearbox, and transmission failures, leading to failed tests. Some of these issues involved premature piston wear, gas leak from head gasket, supercharger spring failure, gearbox bearing damage and gear wear, planetary transmission failure caused by brake belts breaking, bearing failures, and low oil. Other problems noted were the inadequate performance of the radio and poor dust sealing/evacuation of the fighting compartment, decreasing the crew’s combat ability.

In August 1948, Bogdanov once again announced that the military would no longer accept deliveries of the IS-4. In another cat-and-mouse chase between the military, ministry, and factory, the military would once again accept deliveries of new tanks, albeit apparently very slowly. Between September and November, between 40 to 50% of IS-4s built were tested by the military to ensure acceptable operation. In November 1948, IS-4 deliveries were again stopped, forcing the ChKZ to once again try and improve the reliability and operability of the tank by 1 January 1949. In December 1948, 24 IS-4 tanks were tested by the military at ChKZ, of which 10 tanks suffered transmission failures and 8 suffered engine failures.

In total, through 1948, a total of 250 to 450 design changes and improvements were made to the IS-4 during production. On 1 January 1949, out of the 155 IS-4 tanks built in 1948 (the goal had been200 units), 69 tanks were still at ChKZ awaiting shipment. These tanks were stored in halls or outside under tarpaulins, after which it was noted that several tanks had components removed or dismantled. The perpetrators were unknown, but the plant concluded that the pieces were used as spare parts for the military.

Total production was of 224 tanks, though certain sources claim the number was as high as 233, however this is most likely due to ‘double counts’, such as the Prototype No.6 which was actually based on Prototype No.2, or the 1946 pilot batch tanks which were received by the army in 1947. Adding the additional 25 IS-4Ms, the total count was around 250 tanks.

IS-4 Production Numbers						IS-4M
Year	1944	1946	1947	1948	1949	1951
Number produced	5*	6**	46	155	12	25 + 217 converted

* Prototypes (No.0, No.1, No.2, No.3 & No.4)
** At least 6 were production pilot models, accepted into service in 1947

Cost

There were many factors to why the IS-4 faced significant opposition throughout its development and production phase. One of them was the incredible unit cost. Setting aside the near 3 year long development period, in October 1946, a financial report showed that the total cost of production of an IS-4 was 734,580 Rubles, of which 680,000 Rubles was the hull, turret and engine, 40,000 Rubles was the D-25T gun, 12,950 Rubles were the machine guns, and sights and optics were 1,630 Rubles.

Soviet tank costs 1946
Model	IS-4	T-54 (Plant No.183)	T-44 (Plant No.75)	T-34/85 (Plant No.122)	ISU-152
Cost (Rubles)	734,580	352,755	277,230	226,125	561,885

Due to the vast amount of changes made to the IS-4 during its production years, as well as external economical factors, the IS-4’s already inflated price grew even further. These changes required new tooling and equipment and added to the complexity of the tank and its construction. Thus, by 1948, the IS-4 had reached a production cost of 994,000 Rubles. The T-54 from Plant No.183 decreased in cost to 326,000 Rubles in the same period.

The End

Random quality control checks and inspection of the IS-4 production line at ChKZ revealed that several parts and components were not produced correctly or did not match the drawings and technical documentation. This led Marshal Bogdanov to, once again, stop acceptance of the IS-4 by the Red Army, starting 1 January 1949, until the quality of the components would be improved. This became official on 18 February 1949, when a council meeting between the Council of Ministers of the USSR, GABTU representatives, and command of the Armored and Mechanized forces of the Red Army took place to discuss the fate and future of Soviet tanks.

The main resolution was that all development and production of heavy tanks and their derivatives weighing over 50 tonnes would be canceled immediately. This effectively killed various different heavy tank projects, from the troublesome IS-4 to the monstrous IS-7 or Object 718. Instead, ChKZ was ordered to begin development of the Object 730, which would become the T-10, the future of Soviet heavy tanks. Regarding the use of existing IS-4 tanks, the conclusion to the meeting was that the ChKZ was to build a last batch of 12 tanks by May 1949, which would, once again, aim to remove all the issues presented by the military. After state trials, these changes would then be implemented on all IS-4s, including all those already in service.

The requirements imposed by the military were:

• Improving the reliability of the V-12 diesel engine with a warranty of 200 hours, eliminating the issues with damage to the pistons and rings.
• Improving reliability of the planetary transmission by decreasing the wear and damage of the wheels, bearings and drum. The addition of a new 3 to 6 gear 3-step gearbox.
• New air purification system with an efficiency of 100%.
• Decreasing the amount of dust and debris kicked up by the tracks and infiltration of dust and dirt inside the fighting and engine compartment by the addition of shields and covers.
• Addition of a second fan in the turret.
• Remove interference between the radio and the tank’s electrical components.
• Decreasing the stress on the track bearings.
• Addition of ammunition racks.

However, as per a letter from Marshal of the Armored Forces S. Bogdanov, as of 22 April, ChKZ was unable to fulfill the requirements and upgrades imposed on the IS-4, yet the plant continued to produce the tank. As of 6 July, there were 11 hulls ready, of which 10 had the engines installed, as well as having the components ready for assembly for all 12 tanks. Work on improving the tank was advancing, leading to an extension until 15 July granted by the Council of Ministers of the Soviet Union. Of these 12 tanks, only two were actually modernized and were sent to Kubinka Proving Grounds, after which all previously produced IS-4s were to be modernized to their standard, with 40% of the tanks to be trialed at the factory or by the military after their upgrade to check for faults.

Between 1st and 20th September, 10 of the new IS-4s were undergoing military trials, with seven tanks given to the 5th Guards Mechanized Army and three tanks to the 16th Guards Mechanized Division. A series of different trials and tests were done, after which the engines worked for 65 to 70 hours and five tanks had passed the trials and two were excluded from testing due to issues. In total, one engine, two transmission, six roadwheels, and one torsion bar were damaged and required replacement. The tanks traveled between 700 to 1,000 km.

IS-4M

When ChKZ began receiving tanks back from the army, it was noted that the tanks had already sustained large amounts of damage and issues, which first required fixing, increasing the workload and time necessary. Deputy Chief Designer I.S. Kavyarov was in charge of the modernization project. The development and trials of the Object 730, 740, and 750 also further slowed down the process, with the upgrade program eventually being set to be finished in 1951. By this point, 25 IS-4s were built based on existing components based on the military’s upgrade request and were named IS-4M. They were produced in the latter half of 1951. As for the remaining IS-4s, 217 had been upgraded to the IS-4M standard during the same year. In December 1951, the production and upgrading of the IS-4 finally ended, with the technical documentation of the tank being archived in September 1952.

Design

Hull

The hull of the IS-4 maintained the general shape and layout of the IS-2, with the exception of some crucial changes, namely the frontal armor plates, final drive housing and lengthened hull, with a seventh roadwheel. The main upper frontal plate was steeply angled and the rounded cheeks on the IS-2 were replaced by two angled plates connecting between the frontal plate and side plates. The lower hull side walls were flat, while the upper hull sides were slightly angled. To accommodate the lengthened hull, an extra roadwheel was added. The IS-4’s suspension and running gear were virtually unchanged from the IS-2 and IS-3, though a new sprocket design was used and the tracks were widened from 650 mm to 720 mm. On the right side of the hull was the unditching log, while on the left, three stowage boxes were added. On the rear part of the hull, four external fuel tanks were added, as well as smoke generators.

Turret

The IS-4’s turret maintained a similar shape as that of the IS-2. It was built by welding together two large cast segments. By using heavy rounding and angling, a high effective armor thickness could be achieved. On the side of the turret were five handles for the tank riders to hold on to as well as hooks for lifting the turret. A large armored plate, 30 mm thick, was bolted above in the roof of the turret, allowing for easy access for removal of the gun. The commander’s and loader’s hatches were situated on the top of the turret and behind them was the turret ventilation fan. The turret could rotate at 10°/s using the electric drive.

Crew

The IS-4 had a crew of 4:commander, gunner, loader, and driver. Compared to the IS-3, the IS-4 had a much more spacious turret and an improved fighting compartment thanks to the addition of a turret bustle where the main gun projectiles would be stowed. Additionally, a rotating turret floor (30 mm thick) would provide ease of operation when standing as well as additional protection against mines and spalling.

Gunner

The production IS-4’s gunner sat to the left side of the gun. This change was made on prototype No.6, which switched to the 122 mm D-25T gun. He had both an electrical turret traverse and a manual backup. The elevation was controlled manually via a hand crank on the gun. Originally, for amining the gun, he would use an TSh-17 sight with 4x magnification, but this was replaced on production tank with a TSh-45 sight with 3.5x to 7x magnification mounted on the left side of the gun, giving the IS-4 its characteristic hole in the gun mantlet. Above him was the TPU-4-BIS-F-26 intercom, which was replaced with the TPU-47 intercom in 1948. For general vision, he had a rotating MK-4 periscope above him. He had his own service hatch, which would also be used by the driver. The IS-4 was capable of indirect fire, and thus was provided with an angle dial and protractor.

Commander

Seated behind the gunner was the commander, who used a single TPK-1 rotating periscope with magnification of 1x to 5x. To his left was the intercom and behind him the radio station, which was originally a 10-RK-26, replaced in 1948 with a 10-RT-26, in 1949 a 10-RT-26E, and finally, in 1958, a R-113 radio. Both the gunner and commander would share the same service hatch, located above the commander.

Loader

The loader sat alone on the right side of the turret. The projectiles of the D-25T gun were stowed in the bustle facing him, allowing for easier loading. However, the larger propellant charges were scattered across the tank, with only two being on the right side of the turret, the rest being inside the hull. He was also responsible for loading and clearing the 12.7 mm coaxial DShK machine gun. He was given a rotating MK-4 periscope for vision. In front of him, as well as behind the gun breach, were fans for clearing out fumes from within the tank after firing, though the frontal fan was added in the IS-4M modernization. He would also fire the anti-aircraft DShK machine gun, located in front of his hatch on the turret roof.

Driver

Like on most Soviet tanks, the driver sat alone in the front of the hull, in the center. Due to the heavy sloping of the frontal armor, a notable protrusion was added to give more room, though this was not an entry or exit hatch and was welded to the armor. On the early prototypes of the Object 701 (No.0 to 6), the driver had a slit cut out in the armored protrusion for vision. However, before its production run in late 1946, the vision of the driver was changed, with two rotatable MK-4 periscopes being added on the top of the hull. This was likely done as the cutout slit worsened the integrity of the armor plate.

When driving, he would use the left side periscope for general vision and use the right periscope only for correction of the course. However, due to the symmetric positioning of the periscopes, the driver would have to tilt his head to use either of the periscopes, leading to considerable neck fatigue. Furthermore, the driver’s seat lacked elevation controls, potentially leading to the driver having to sit in very awkward positions.

The IS-4 was also notably hard to drive. During several trials, it was noted that the clutch was hard to press (this was slightly remedied), and the steering tillers were stiff and required force to move. It was concluded that the IS-4 was not a tank for amateur drivers and required practice and training to get the hang of it. In at least one trial, it was noted that the trial driver (noted to be experienced) had unintentionally stalled the engine several times.

The two pericopes were mounted on a hatch that could be elevated and slid to the side, however due to the bulkiness of the turret, it was impossible to enter and exit via this hatch, and it was only to be used during non-combat maneuvers. Instead, the driver had to make his way in and out through the fighting compartment and out through the turret hatches. In case of emergency, the driver had an escape hatch in the hull floor, which was inconveniently placed behind his seat.

Armament

The IS-4’s main armament was the tried and tested 122 mm D-25T gun, present on the IS-2 and IS-3, although the Object 701 prototypes were equipped with either the 100 mm S-34-1 or 122 mm S-34-II guns. The gun could depress to 3° and elevate to 19°. Due to the two-part ammunition of the gun, the maximum rate of fire was of only 2 to 3 rounds per minute.

The rounds of the D-25T weighed 25 kg (projectile) + 15 kg (cartridge) and had a muzzle velocity of 781 m/s when fully charged with an accuracy equivalent to hitting a 2.5 m tall target from 1,100 m. Maximum firing range was 13,500 m.

The tank was equipped with BR-471 Armor-Piercing (AP) rounds and OF-471 High-Explosive (HE) rounds. For improved armor penetration, the tank was likely equipped with either BR-471B and/or BR-471D rounds.

Armor Penetration of D-25T AP rounds (mm)
Round	Angle (from normal)	Range (m)
		500	1,000	1,500	2,000
BR-471	0°	150	130	115	100
	30°	120	105	95	80
BR-471B	0°	155	145	135	125
	30°	125	120	110	100
BR-471D	0°	185	170	155	145
	30°	150	140	125	115

Source: Domestic Armored Vehicles 1945-1965

Secondary armament consisted of two 12.7 mm DShK machine guns, one mounted coaxially to the right of the gun and one mounted on the roof of the turret, in front of the loader’s hatch. It had a range of 1,500 m and could be aimed with the gunner’s TSh-45 sight. It used B.30 AP bullets, as well as AP incendiary B-32 and BS-41 bullets.

Ammunition consisted of 30 (28 in the turret, 2 in the hull) 122 mm rounds, 1,000 12.7 mm rounds, and 29 F-1 hand grenades.

Armor

Perhaps the biggest merit of the IS-4 was its impressive armor. Through the use of heavy sloping of the hull as well as rounded casting, the tank had some of the best protection of any heavy tank of the time. The upper frontal plate was 140 mm thick, angled at 61°, while the lower frontal plate was 160 mm thick, angled at 40°. Side armor plates were 160 mm thick. The frontal and side plates were united via “cheek” plates, 140 mm thick and angled at 55°. The complexly shaped rear was 100 mm thick. The hull deck and final drive deck were 30 mm thick.

The turret was even thicker, consisting of 250 mm rounded cast armor at the front, tapering to 200 mm at the sides and 170 mm at the rear. The roof of the turret was 30 mm thick.

Powerplant

Early in its development, the Object 701 was to be fitted with the V-12 engine developed by ChKZ in February 1943. It could output 750 hp at 2,100 rpm and was fitted with a centrifugal turbocharger from an AM-38 aviation engine. The engine was based on the tried and tested V-2 and using the turbocharger, the motor was able to increase the air pressure for the combustion chamber, leading to higher crankshaft RPM. However, due to this increase in RPM, the engine would deteriorate much quicker, requiring more fuel changes and experiencing higher forces and temperatures, leading to unreliable operation, a mainstay “feature” of the IS-4. The starter engine was an electric ST-700 outputting 15 hp or alternatively using compressed air via two 5 liters cylinders. The tank’s driver also had the controls for the cold engine starter, which heated the air in the cylinders.

The air filters on the IS-4 consisted of a two-stage filter system called Multicyclone, but during trials, it proved to be faulty and would last for just 6 hours of operations, after which the filters needed cleaning, a timeframe during which the engine could not be used. The inadequate air purification system was just another factor to the poor reliability of the V-12 engine.

Transmission and Gearbox

Due to the 15 tonnes difference between the IS-4 and the IS-2, a new transmission had to be designed. The Object 701’s original gearbox was developed between ChKZ and the Bauman Moscow State Technical University, with all elements of the transmission being mounted within a crankcase, with the exception of the final drives, to the left and right of the crankcase. The mechanical planetary transmission had six forward speeds, three reverse, and two neutrals. A pressurized oil system lubricated the transmission and hydraulic servos eased its operation by the driver.

A “ZK” style steering mechanism was used, the system originally being created for the T-38 by engineers G.I. Zaychik and M.K. Christie. This system automatically increased the torque of the sprocket, thus not requiring the brakes or downshift in gears, and being capable of neutral steering. However, as per N.F. Shashmurin, the system would lead the tank to become more unstable and hard to control on slopes or slippery terrain.

Cooling System

Upon capturing and studying the German Panther tank, the Soviets quickly began helping themselves to the various systems and technologies used. One of these was the engine cooling and air intake system on the IS-4, which was essentially just a Soviet copy of the Panther’s German system. The reason for this was due to the additional heat created by the turbocharged engine, requiring a new system compared to that of the IS-2. As per the German solution, the IS-4 featured two large exhaust fans with air intake radiators on either side of the fan, mounted in isolated compartments, preventing damage to the engine in case of a Molotov cocktail attack or dusty conditions. The system would eventually prove to be unrefined and unreliable, with 10-15% power loss from the drive shaft to the fans, as well as other small issues. A heater for the cooling system was provided, which would heat up the coolant.

Fuel Tanks

The IS-4 featured three internal fuel tanks with a total fuel capacity of 450 liters, enough for 140 km on roads. As was common on Soviet tanks, four additional external fuel tanks were mounted on the hull, initially on the sides, but two of the tanks later moved on the rear part of the side fenders to better protect them against damage and enemy fire. These fuel tanks were of 90 liters each (total 360 liters), which could increase the range to 250 km.

Variants

Command IS-4

The need and technical requirements for a command tank variant of the IS-4 was laid down by Head of the GABTU Lt. Gen. B.G. Vershinin and Chairman of the GABTU Maj. Gen. Eng. N.I. Gruzdev, on 5 July 1946. The project was headed by G.N. Rybin. It required several changes to the standard IS-4 by reducing the ammunition by 50% and the remaining ammunition to be stored in the hull. To aid the officer’s task, the tank was to feature a folding table and good lighting for using maps and documents, as well as a waterproof bag for storing papers. A series of vision equipment were to be provided as well, including a rangefinder, telescopic periscope with 6x magnification, and IR night vision devices. Other changes included increasing the size of the turret hatches by 20 to 25%, the addition of two new radios for different types of communication, and a radio operator. It is noteworthy that the tank was not to lose its main firepower capability and was to be virtually identical to the serial IS-4 externally. Plant No.100 was to build a prototype in November 1947, but this did not happen and the project was abandoned in October 1949.

Flamethrower IS-4

A flamethrower variant of the IS-4 was requested on 21 November 1946 by the scientific tank committee at GABTU. It was to have internal fuel tanks of 200 to 300 liters compensated by the removal of main gun ammunition. The main fuel source was located in an external 5-tonne trailer, with a capacity of 1,500 liters of combustible fuel, or 100 to 150 shots. The trailer was also considered to be equipped with chemical warfare systems, such as poison gasses, smoke screens, and a degassing station. For safety, an automatic CO2 fire extinguisher was to be added, as well as a latch for detaching the trailer in case it would catch fire. Technical documentation was to be ready by August 1948, but the project was abandoned.

Object 715

In the following years after the end of the Great Patriotic War, the Soviets still pursued the idea of heavy self-propelled guns based on heavy tank platforms. One of these was the Object 715, which much like the Object 704 based on the IS-3 chassis, would use the IS-4 chassis and a large armored casemate to house the massive M-31 152 mm gun, developed at Plant No.172. It was to be designed by November 1948 and featured the standard layout of Soviet heavy self-propelled guns. However, besides a partial blueprint of the casemate and gun, the project did not progress further due to the premature stop of the IS-4 production as well as the cancellation of development and production of all heavy tanks above 50 tonnes, and subsequently, all projects based upon them.

Object 717

Unfortunately, not much is left about this project, aside that it was to be a bridge-layer vehicle based upon the IS-4 and be allocated to heavy tank divisions. This likely would have required the removal of the turret and addition of an extendable/foldable bridge with a capacity of at least 60 tonnes.

ST-I & ST-II

In 1945, experienced military engineer V.A. Ganin proposed a deep upgrade based on the hull of the Object 701. His reasoning was that tanks at the time had several flaws which decreased their efficiency and combat value. He categorized and identified over 28 fIaws in existing tank designs and proposed a series of changes. In his designs, he would improve upon the Object 701 by enlarging the turret, increasing roadwheel diameter, the addition of a 2-axis stabilizer for the main gun/turret, a mortar mounted turret, adding flexible air intake for wading underwater, as well as other changes. His tanks would be called ST-I and ST-II, with the difference being that the first had a single 100 or 122 mm main gun, while the second had a dual 100 or 122 mm gun, mounted in parallel.

Upgrade and Experimental Projects

In November 1946, GABTU ordered the research and development of wet ammunition stowage for several heavy tank projects, including the IS-4. This project was headed by S.V. Fedorenko at the SKB-2 design bureau, however the project was canceled after delays.

In spring 1947, the LKZ and Plant No.9 were working on implementing a weapon system for the IS-4 that would include a 14.7 mm and 7.62 mm machine guns. The project was named D-35 and the first prototype was to be built and trialed by December 1947. Due to delays, a prototype was only built by October 1948, after which the project was canceled.

Another project involving the 14.7 mm KPV heavy machine gun involved anti-aircraft installments based on the DShK mount, a remote controlled mount and a pair-machine gun in a turret. Development began in December 1946 under the leadership of G.N. Rybin, but due to issues with the mounts, it was concluded that the mount had to be changed to a rotating ring mount. Work continued until the end of 1948, and although it was never mounted on the IS-4, the project was incorporated onto several new heavy tank projects, including the Object 262, 272, and 734. Regarding pair-mounted KPVs in a turret, no prototypes were built, but the knowledge was applied on other projects, such as the Object 718 and 726.

In March 1947, a night vision IR spotlight was mounted on the mantlet of an IS-4, along with an IR night vision sight for the gunner, as well as a night vision system for the driver and nighttime position lights fitted with IR filters. The tank was tested in April 1948 at the Kubinka Proving Grounds. The gunner’s IR sight was welded to the gun mantlet and aligned to his standard sight. The project did not yield positive results and work was discontinued.

Improving the survivability of the IS-4 was also considered, with proposals of thickening the armor in several weak spots, including the turret hatches (from 20 mm to 30 mm), the engine grilles (from 20 mm to 45 mm), the lower frontal plate, and engine deck hatches. Another proposal was the addition of sideskirts and screens, meant to protect the tank against shaped charged projectiles and RPGs. Firing trials were done at Kubinka on ballistically accurate mock-up hulls of the T-54, IS-4, and IS-7, produced at the Izhora Plant, but the sideskirts and their mounts proved to be fragile and ineffective, thus the project was canceled. Two types of skirts were used for the IS-4, a 5 mm thick solid steel sheet, and a 5 mm thick perforated sheet. The sheets were mounted to the hull via large arms, which kept the plates between 600 to 735 mm away from the tank’s hull, increasing the total width by 120 cm.

Work also continued on replacing/improving the transmission on the IS-4. In March 1949, 30 changes were made on the planetary transmission and were tested on five IS-4 tanks. These included the addition of an improved oil pump which decreased wear on the bearings, increased the amount of lubricant in the gearbox, increased the cooling capacity of the transmission and many other more technical changes. A hydromechanical transmission was also developed under leadership of A.D. Kryukov in 1947, work which was later implemented on the Object 266. Similarly, an electromechanical transmission was also developed under leadership of L.B. Tevelev, with the work being used on the Object 260.

Further work on the tracks of the IS-4 was done in spring 1948, at the order of the Head of GABTU, Lt.Gen. B.G. Vershinin. Track extensions were developed to decrease the IS-4’s ground pressure in soft terrain, such as mud and snow. The project was initially launched in 1946, also headed by Yakovlev. The extensions would attach to the outside of the regular track link and weighed less than 50% of the track link (16.4 kg). Attaching them took 30 minutes and dismantling them took 20 minutes, though a device could be installed to automatically detach the extensions. Testing was done in 1948 at Kubinka and it was measured that the extensions decreased the ground pressure from 89.7 kPa to 61.8 kPa. However, this came with a great cost. The tank could reach a maximum speed of 10 km/h (interesting to question is how fast the tank could travel without the extensions) and decreased the maneuverability of the tank. Additionally, when driving through 70 cm deep snow, the difference in depth between regular track and extended track was of just 20 mm. Photographic evidence also shows that, after 38 km into the trials, a large portion of the extensions were broken off or bent out of position. Due to these faults, the project was not pursued any further.

Service

Originally, the IS-4s were to equip heavy self-propelled tank regiments, which consisted of a heavy tank battalion (21 tanks) and a heavy SPG battalion (21 SPGs). However, by an order given 22 July 1947, the first eight IS-4s to enter service were given to the Chelyabinsk Tank Technical School and the 30th Tank Training Regiment, with four tanks respectively. The first active service unit to receive the IS-4 was the 5th Guards Mechanized Army, located in the Belarussian Military District. More specifically, the IS-4 tanks were given to the 93rd Guards Heavy Self-Propelled Tank Regiment of the 29th Tank Division. However, due to the low and slow production of the IS-4, only one unit was fully equipped with IS-4s. In late January 1949, this unit took part in a military exercise meant to test the reliability and capabilities of the modernized IS-4M as well as T-54 tanks. In February, the Commander of the Armored and Mechanized forces of the USSR S. Bogdanov sent a report to Marshal of the Soviet Union A. Vasilevsky regarding the result of this exercise:

“I report that from January 25 to 29 this year an experimental exercise was conducted with the 93rd Guards Heavy Self-Propelled Tank Regiment of the 29th Tank Division in order to test and study the performance of the IS-4 and T-54 tanks, and check the reliability of the units of these vehicle in military operation conditions, as well as night time shootings.

In total, 61 tanks (of which 46 IS-4 and 15 T-54 tanks) [note by author: as well a sa variety of other vehicles including BA-64s, trucks and cars] took part in this exercise.

But the results were disappointing for the IS-4 tanks: the vehicles were found to have a significant amount of shortcomings, and the measures taken by the plant to improve the tank’s reliability did not yield positive results.”

Once the IS-4 production was stopped in February 1949, the discussion of what to do with the remaining tanks appeared. It was concluded that once the new heavy tank (T-10) would enter service, It would replace the IS-4 with the 5th Guard Mechanized Army and instead all IS-4s were to be moved to three new, heavy tank regiments, consisting of 68 tanks each (total of 204 tanks).

One of these divisions should be part of the 5th Guards Mechanized Army, one part of 7th Separate Cadre Tank Division, and last one to belong to the 8th Mechanized Army.

However this could not be achieved due to the low number of available IS-4s. At the end of May 1950, there were 217 IS-4 tanks in service, of which 78 were at the factory undergoing repairs, leaving just 139 in service, enough to fill two regiments. Between 1950 and 1951, the IS-4s were sent in batches to ChKZ for modernization and repairs, after which they were sent back to the aforementioned units in the Belarussian Military District.

In 1954, heavy tank divisions were formed, which consisted of three heavy tank regiments (65×3 tanks). By 1957, eight heavy tank divisions were formed: 14th Guards, 18th Guards, 5th, 13th, 17th, 24th, 25th, and 34th divisions. These consisted of IS-2, IS-3, and IS-4 heavy tanks taken from the now disbanded self-propelled heavy tank regiments, though a small number of T-10s were available as well.

In the 1960s, the IS-4s underwent another round of refurbishment, after which they were placed in storage in Osipovichi.

The last tanks were noted to be in service in the early 1970s at units like the 240th Tank Training Regiment in the Far East District.

Worthy of note is that the abysmal reliability of the IS-4 was not only contained to trials and factory tests. During service exercises with troops in January 1949 involving 46 IS-4 tanks produced in 1948, several issues and quality-of-life problems were encountered. During firing exercises, it was noted that some high-explosive shells did not fit in the stowage racks, with two shells situated vertically in the hull body having their fuse caps removed accidentally by the seats of the commander and loader. This flaw was already known, and it had been instructed that longer shells would not be used until the flaw was remedied. Another flaw was the current created by the internal engine air intake, which drew air in from the fighting compartment. This pushed cold air from outside through the crew’s hatches, being notably worse for the driver, as the rushing air brought in snow or dust into his face. The layout of the service hatches and common service points was poorly designed, making regular maintenance tedious, for example changing the oil and air filters, changing the batteries, and it was “nearly impossible” to clean the transmission compartment from dust. After one to two hours of operating the engine, the entire rear part of the hull would be covered in soot from the exhaust pipes. When reloading or clearing jams in the coaxial DShK machine gun, the main gun had to be elevated to 10° or 12°. The spare parts and tools on the tank were also lacking, as there were no tools and jacks present for removing several components, such as the return rollers. Lastly, previously noted problems were present once again, such as poor visibility for the driver, high accumulation of gasses within the turret, and loud engine cooling fans.

Static Fortification Conversion

Between 1949 and 1953, at the North Central Research Institute, under the leadership of engineers S.G. Gilbert and A.D. Denisenko, static defense turrets using the turrets of the IS-3 and IS-4 tanks were designed. This was part of a greater plan to fortify the USSR, intending to use specifically designed static turrets, the turrets of tanks already in service and concealable light turrets, which could be lifted and moved. Prototypes of such systems based on the IS-3 and IS-4 were made at ChKZ and tested on bunkers. After successfully passing trials, they were put into service across the USSR.

The turrets were fitted with the standard IS-4 armaments and vision devices, as well as a TSh-2-21 telescopic sight with 4x magnification and ammunition count of 80 rounds. The system had a crew of 3. To power the system, 12 6STEN-140 batteries were used. The turrets would be mounted on top of underground bunkers made out of prefabricated concrete modules. These were fitted with separate rooms with sleeping quarters, ammunition stowage, etc.

However, by the mid-1950s, the interest in such emplacements dropped drastically. Many of the existing turrets were put into conservation and the personnel manning such fortifications was significantly cut, with some garrisons being completely disbanded. Maintenance crews were created, but these were also removed and the turrets were left abandoned.

This did not last long, as by the 1960s, tensions between the USSR and the People’s Republic of China (PRC) began to grow, with constant border violations and the testing of nuclear weapons by the Chinese. In 1965, China created a 200 km exclusion zone and brought troops near the Sino-Soviet border. Thus, amongst other mobilization plans, the Soviet fortifications from the Transbaikal and Far East were revitalized and made combat-ready. In 1966, special fortified areas were created, such as the 31st (Transbaikal), 97th (Zabaikalsk & Dauryia), and 114th (Sherlovaya Gora) areas. These consisted of a machine gun battalion, artillery battalion, artillery division, missile battery, and four tank battalions. The tanks used in these fortified areas varied from T-34/85s, to T-54s, and OT-54s.

However, due to the escalation of military and political hostilities in the late 1960s, and most notably the Damansky Island incident, the Western and Far East Military Districts reactivated and built new bunkers. In east Transbaikal, three new fortified areas were created, 11th (Priargunsky District), 18th (Krasnokamensk), and 19th (Bilituy village). Old and unused tanks supplied by the Western Military District were brought here and their turrets were dug in and used as makeshift fortifications called НТОТ (NTOT, fixed tank firing point). One such case was in the Dauryian fortified area, where unused IS-4 tanks from the Belarussian Military District were brought in 1969, but these could not be used effectively due to their wear and age. Thus, alongside IS-2 and IS-3 tanks, their hulls were cut out and the turrets placed as fortifications. There were cases of T-54 and T-55 turrets being used as well. Estimates range from 950 to 1,500 tanks were sent to these fortified areas during this period. Not just the tanks sent to these areas were old, but also the machine guns, ammunition, radio stations, as well as other equipment were noted to be old, worn out and complaints were noted during the training exercises made during autumn and winter 1969. In total, in the Transbaikal Military District, six battalions of fixed tank firing points were made.

Fortifications were also made in the Vladivostok region by the Vladivostok Defense Region (part of the Pacific Fleet), with 1st Area in Artyomovsk Coastal Defense Sector, and was equipped with a company of tank firing points. In the late 1970s, fortifications in the Kuril District of the Sakhalin region were also made, with tank turret emplacements across several islands. A crew was assigned a battery every day, and combat readiness of the systems was of 5 minutes for two turrets and 15 for the remaining. By the end of the 1980s, besides the improvement of the Sino-Soviet relations, new types of fortifications began being used, being equipped with modern Anti-Tank Guided Missile (ATGM) systems.

In 1997, an agreement between Russia and China was signed, demilitarizing the 200 km border along the Transbaikal. The tanks and fortifications were abandoned, leading to destruction and looting by the locals. In the 2000s, turrets mounted across the Karelian Isthmus and Leningrad region were scrapped. The last static defense turrets were scrapped in 2011 and 2012 from Site No.4 near Nakhabino, a few km north-west of Moscow, though there are likely still turrets lost in remote areas of Russia and former USSR states, such as Kazakhstan, as per occasional photos emerging on the internet.

Analysis

It is not difficult to come to the conclusion that the IS-4 was a failed tank, but perhaps the more valuable evaluation would be regarding why this happened. The IS-4 was born at a time where the tide of the war was turning, and the Soviet defense industry was in full swing. Due to mechanical issues and unreliability, by the time of the first “production worthy” prototypes, the war was nearly over, and the defense industry was preparing for civilian production. Factoring in that the IS-3, designed and built by the same factory, had entered service, the entire point of the IS-4 was gone. It is often said that the IS-3 missed the war, in which case the IS-4 never even arrived, literally and figuratively. Perhaps the story of the IS-4 should have ended here, much like its early rival, the IS-6.

Except that, due to the dissatisfaction with the IS-3 and rising tensions between the East and West, the IS-4 was brought back to life. Yet a new set of challenges stood before the tank. Its original mechanical problems were never fixed and the brain-drained defense industry was severely struggling with fixing and improving a tank which had already been in development for several years. Besides the awfully unreliable powerplant, transmission, and various other components, the large weight of the tank did not help its situation. While in 1944, the armor profile was seen as the best in the nation, by 1947, despite changes, it was no longer justifiable. The D-25T main armament found on the IS-2 and IS-3 was also growing obsolete, in an era where more advanced ammunition types outclassed conventional rounds.

Ultimately, the final decision about the strengths and weaknesses of the tank was made by its users, which would deploy it in the Far East and along the China border and would be retired from service rather quickly, with the last traces of them being used as training tanks or bunker emplacements in the 1970s.

Survivors

Due to the short production run and regretful fate as fixed firing points, most IS-4s have been scrapped, with only three survivors being on public display. One, and perhaps the most famous, is the IS-4M at Kubinka (now Patriot Park). Another is at the Officer House Garrison in Chita. And a third one can be seen at the Semey open air military museum in Kazakhstan. Several other IS-4s are located in various stages of decay in western Kazakhstan, most notably in the Druzhba village.

Conclusion

The IS-4 proved to be a complex and expensive tank that, despite colossal efforts and investments, was never refined and was cursed by reliability problems due to its heavy weight and troublesome engine and transmission. The rough post-war scenario in which it was developed did not help its success either. Despite its thick armor, the D-25T main gun and general layout began to quickly become archaic, and much like the IS-3 it was meant to substitute, it was based on Second World War theory, while the post-war scene was rapidly evolving towards more performing medium tanks and missiles. Its short production run and service life make it one of the very few Soviet vehicles to enter service but never see combat. Today, it remains overshadowed by the more glamorous IS-3, colossal IS-7, and genuinely capable T-10 heavy in terms of post-war Soviet heavy tanks, the USSR being one of the last nations to give up on the idea of the heavy tank in the 1960s.

IS-4 (Object 701) Specifications
Dimensions (L-W-H)	9.790 x 3.260 x 2.480 m
Total weight, battle-ready	60 tonnes
Crew	4 (commander, gunner, loader, & driver)
Propulsion	V-12, 12 cylinder turbocharged diesel, outputting 750 hp.
Speed	Max. 43 km/h Avg. ~20 km/h
Suspension	Torsion bar, 7 bars per side
Armament	122 mm D-25T 2 x 12.7 mm DShK machine guns (coaxial and roof AA)
Armor	UFP: 140 mm @ 61° LFP: 160 mm @ 40° Upper Hull Side: 160 mm @ 30° Lower Hull Side: 160 mm flat Rear Hull: 100 mm Hull belly and deck: 30 mmTurret front: 250 mm Turret side: 200 mm Turret rear: 170 mm Turret roof: 30 mm
No. Built	224 IS-4 + 25 IS-4M

Sources

IS-4 Operator Manual

Soviet Heavy Tank IS-4 – Maxim Kolomiets

Stalin’s Superheavy tank IS-7 – Maxim Kolomiets

Domestic Armored Vehicles 1941-1945 – A. Solyakin, I. Zheltov, I. Pavlov, M. Pavlov

Domestic Armored Vehicles 1945-1965 – Ivan Pavlov, Mikhail Pavlov

IS Tank – Igor Zheltov, Alexander Sergeev, Ivan Pavlov, Mikhail Pavlov

Armor Collection No.3 1996 – Mikhail Baryatinsky

Designer N.L. Dukhov and his School – Yu.V. Rozhdestvnsky, V.N. Bondar

TiV No.1 2013 p.47-60 – M. Pavlov, I. Pavlov

IS-4 tank (btvt.info)

Tank Archives: IS-4 Start to Finish

Tank Archives: Object 701 Trials

Forum icvi.at.ua

The Heaviest Tank of the USSR | AllAboutWarThere | Zen (dzen.ru)

IS-4 – The Epic Fail of Soviet Post-War Tank Building | Stalinium armor, comrade! | Zen (dzen.ru)

Tank 701 – From First Prototypes to IS-4 | Stalinium armor, comrade! | Zen (dzen.ru)

IS-4 in real operation | Stalinium armor, comrade! | Zen (dzen.ru)

IS-4: From “Reliable” Prototypes to Complete Failure | Stalinium armor, comrade! | Zen (dzen.ru)

How to make screen armor? Soviet recipe 1948 (topwar.ru)

Забайкальские укрепрайоны. Разграбленная мощь. – Хроники “Вьетнамских комсомольцев” — LiveJournal

Tank OT based on IS-4 – KaUR, APK-museum (nortfort.ru)

Fortifications with tanks – 0011.htm (narod2.ru)