Object 263 Development

"Brief report on the results of experimental, scientific research, and test production at VNII-100 in June of 1950

Topic #1: heavy ISU-130 SPG on the chassis of the new heavy tank

The development of the ISU-130 (Object 263) technical project was completed in June of 1950. 

Two sets of overall blueprints and detailed blueprints of specific components as well as an explanatory memo were sent to the Ministry of Transport Machinery with letter #1035ss on June 28th, 1950.

To resolve issues connected with the development of the technical project by the Institute as of July 1st, 1950, the following experimental work was performed.

The Last Soviet Heavy Tank Destroyers

In the days of the Second World War, heavy self propelled guns played an important part on the battlefield. It is not surprising that after the end of the war, heavy SPGs, including tank destroyers, remained a priority for designers from all nations. It's surprising that only a handful of these vehicles were ever built in metal, and none were mass produced. The Soviet Union and its Object 268 was no exception.

Unlucky Seven

Soviet post-war Object 752 and Object 777 heavy tanks were, for their time, the height of daring and originality. The designers had to strike a balance between requirements to increase armour and limits on mass. These restrictions resulted in very compact and well protected tanks with a dense, but reasonable layout. However, the era of heavy tanks was over, and these excellent designs did not move past the model stage.

Replacement Tank

Experience with the IS-4 and IS-7 turned up one unpleasant fact: no matter how perfect your tank is, a weight of over 50 tons is a one way ticket to nowhere. There were several reasons why the IS-7 did not make it into production, but its mass of almost 70 tons isn't the least important. Instead, SKB-2 and NII-100 joined forced to develop a 50-ton tank that combined the progressive solutions of the IS-4 and IS-7. This tank was indexed Object 730, the improved tank received the index IS-8, and the tank was put into production under the index T-10.

The T-10 was less protected than the IS-7 and had an inferior gun, but there weren't any unusual problems that arose when the tank was adopted to replace the IS-2 and IS-3 on December 15th, 1953.

Even while the IS-8 was undergoing trials, talk started regarding its replacement. Such an arrangement might come as a surprise to come, but there is nothing strange here. The late 1940s and the 1950s were a time of rapid development in technologies, plus the Korean War served as an additional boost for tank designers, showing that no pause in tank growth is coming.

While tanks were being built abroad to fight the IS-3 that so impressed the Western viewers of the parade in Berlin, the USSR managed to go through two generations of heavy tanks. Perhaps it would be the right move to drive a few IS-7s down Red Square and provoke the West to create armoured beasts in return, but nobody was thinking of informational warfare. The army needed real tanks.

Research of organizations like NII-48, which studied armour, encouraged a change in generations. The employees of this institute designed a series of solutions that allowed to drastically improve levels of protection without significant increase to weight. This included the "pike nose", variable thickness castings, V-shaped hulls. The T-10 looked obsolete in an instant. Yes, it had a series of novel solutions from the IS-3 and IS-7, but these were solutions from the 1940s.

The artillerymen did not sit still either. For several reasons, the IS-8 received the D-25T gun, which the military was already dissatisfied with in 1944. Additionally, Soviet intelligence carefully tracked the tanks built by potential foes, including the T43 (future M103 Heavy Tank). A successor to the IS-8 was necessary.

Work on creation of a new tank was initiated by the Ministry of Transportation Machinery in late June of 1952. SKB-2 from ChKZ under the direction of M.F. Balzhi was chosen as the developer. In February of 1953, he was replaced with P.P. Isakov. The first drafts were ready by the end of 1952, and in June of 1953, a year after being given this task, SKB-2 presented their project. Or rather projects, since at this point there were two designs. One, Object 752, was developed within the IS-3's mass range. The other, Object 777, was limited by the IS-8's mass.

From the start, SKB-2 was faced with a very difficult issue: creating a tank that, while being lighter than 50 tons, would be superior to the IS-8 in every way. Similar problems were solved before: remember the IS-3 that was significantly better protected than the IS-2. The situation repeated itself, thanks to new scientific achievements made by hull designers.

A new concept of armour was used when designing the Object 752 and Object 777, a landmark in armour technology. In these tanks, different armour plates were not only different thicknesses, but the plates themselves changed thickness. This allowed the designers to achieve unprecedented levels of armour protection while staying within mass limits.

Object 752

The Object 752 was a lot more conventional than its heavier brother, but still very interesting. The dense layout resulted in the tank being only 2300 mm tall (150 mm lower than the IS-8). Recall that this is a fully fledged heavy tank. If in the West, medium tanks already approached (and in the Centurion's case, crossed) the 50 ton barrier by 1950, the Soviet classifications did not change, and the 45.3 ton tank remained a heavy.

From a technical standpoint, the Object 752 had nothing revolutionary about it. It was a classic Soviet heavy tank with six road wheels per side on a torsion bar suspension with a rear engine and hydraulic transmission. The tank was powered by an 800 hp V-12-6 engine used on the IS-8.

According to calculations, the top speed of the tank was 50 kph, with an average speed off-road of 30 kph. The suspension was interesting, as there was a proposal to use a hydraulic suspension with road wheels reminiscent of the IS-7's.

The hull design was much more interesting. The work of hull designers was already highlighted in this article, and for a good reason. Thanks to the new hull design, the Object 752 had equivalent, and in places superior, armour compared to the IS-7. The front of the hull had 215 mm of armour, more than the German Maus and E-100 tanks. Remember that this is a tank that weighed only 45.3 tons.

These mind-boggling results were achieved through the use of casting that allowed variable thickness parts to be made. The thinnest part of the upper front plate was only 90 mm thick, but it was placed at such an angle that it would only be penetrable from a nosedive. The sides were 125 mm thick, but placed at such angles that they guaranteed complete protection from the 88 mm Pak 43. The angles were reasonable enough to leave plenty of room inside for equipment, which was better than NII-100's designs, whose sloped sides often caused layout issues. The turret of the Object 752 was more conventional, and similar to the IS-8's turret. The front part was 260 mm thick, the sides 150 mm thick.

The armament was also revolutionary. The main gun was the 122 mm M-62-2T gun with a muzzle velocity of 950 m/s. This tank was the first where this gun was used. Due to the dense layout, there was no coaxial machinegun. A collapsible mount with a 14.5 mm KPVT machinegun was mounted on the roof by the loader's hatch to protect the tank from low flying aircraft.

The creators of the Object 752 included a loading mechanism. This was not a fully automatic loader, but it noticeably sped up the loading process. Despite the densely packed fighting compartment, there was room for 40 122 mm shells, 10 more than in the IS-8. There was also an alternative proposal with an almost completely automatic loading mechanism. In this case, 28 shells fit along the turret's perimeter (15 AP and 13 HE), and the loader only had to pass in the shells. Drawbacks included less ammunition and a more crowded fighting compartment.

There was an alternative armament proposal, a much more original one. Instead of an IS-8 type turret, SKB-2 designed one that resembled AMX-13 and AMX-50 turrets. The degree of influence of French projects on this design is questionable, but it's doubtful that the public demonstration of the AMX-50 in July of 1951 was ignored by Soviet intelligence.

To be fair, the two turrets only share the general concept. SKB-2 shied away from drum type canisters and only implemented a partially automated loading system, keeping the loader in place. The internal volume of the turret decreased. Interestingly enough, the oscillating turret did not have an AA machinegun, but the coaxial SG-43 machinegun returned. With this new turret, the Object 752 was only 2150 mm tall, lower than a T-26.

Object 777

The heavier Object 777 was a much more revolutionary design than its brother. Judging by the presentation, this was the more promoted project. Unlike the Object 752, where the use of existing components was encouraged, the Object 777 was much more conceptual.

There were two options for the engine, liquid cooled and air cooled. Both projects, indexed V-7, were designed by the ChKZ diesel engine design bureau under the supervision of I.Ya. Trashutin. The air cooled variant was considered higher priority, as it was smaller.

To compare, the length of the IS-8's engine compartment was 3480 mm, the Object 752's was 2410 mm, and the Object 777's was only 2300 for the liquid variant and 2100 for the air cooled variant. Such a drastic reduction in length was possible due to positioning the engine perpendicularly, a first for heavy tanks. As a result, the turret could be moved closer to the center, which had a positive impact on the tank's balance and precision of shooting, especially on the move.

The engine was only one new feature of the tank. With a mass of 49,800 kg, it combined a large amount of innovative solutions. The lighter Object 752 was very low for a heavy tank, but the Object 777 was even lower. The height of the turret hatches was 2100 mm, even less than the T-64, T-72, and T-80.

Thanks to a more powerful engine (850 hp), the speed of the tank was at the level of the Object 752, but with a smoother ride. The smoothness was achieved by lengthening the suspension by one road wheel and a superior weight distribution. The tank also had several variants of hydraulic suspensions, as well as a torsion bar and hydropneumatic suspension. In addition, the tank had a planetary 7-speed gearbox.

The hull of the Object 777 was similar to the Object 752, but there were some notable changes. The maximum thickness of the UFP was reduced to 175 mm, but at a sharper angle, which reduced the weight while retaining the level of protection. As with the Object 752, the driver's seat was shifted slightly to the left. This made entering the vehicle easier and made it harder for the driver to his his head on the gun when his seat was fixed in the travel position.

The liquid and air cooled variants differed externally. The roof of the engine compartment had an air intake for the centrifugal air filter. As for the water cooled variant, it had a different shape of the rear and roof to accommodate the larger radiator.

The turret was similar to that of the Object 752, but with some changes. The front was only 195 mm thick, but due to a more extreme slope, it retained the same level of protection. The sides were 215 mm thick, making them impenetrable for the German 128 mm gun used on the Maus. The mechanical loader was not used. The Object 777 kept the coaxial SG-43 machinegun. The liquid cooled variant had the same AA mount as the Object 752, but the air cooled tank got a remote controlled AA turret on top of the main turret.

Both projects were sent to the Ministry of Transportation Machinery in June of 1953. After some discussion, the layout of the Object 777 was changed. A wooden 1:10 scale model was also made. Work on this very interesting project continued until 1954, but sadly, did not progress past models.

However, the effort did not go to waste. Solutions used in these projects went on to be used in the Object 770 tank. The shape of the hull and turret are reminiscent of its predecessor. Additionally, the experience was used to modernize the IS-8/T-10. In 1957, the T-10M entered production, armed with the 122 mm M-62 gun.

Original article by Yuri Pasholok.

The Last Soviet Heavyweight

The last fighting machine named after Stalin would be the last Soviet heavy tank. It appeared at a time when the trend of constant increase in the weight of tanks came to a stop. Without the ability to grow protection and armament of tanks at the expense of weight, the designers of the IS-8 (T-10) used a number of creative solutions.

The end of an era of giants

Starting from late 1943, Soviet tank designers steadily increased the mass of their heavy tanks. Eventually, the initial stages of tank projects stepped over the psychological limit of 50 tons. The IS-3 was an exception, but it was essentially a deep modernization of the IS-2. Interestingly enough, there were doubts at the very top of the Main Armour Directorate (GBTU) about the suitability of the IS-3 for service. The Object 701, which hit a mass of 55 tons during the prototype phase, seemed much more desirable. Development of the future IS-4 was moving slowly: the first prototypes were ready for the summer of 1944, but the tank was constantly changed, and, despite being designed as an answer to the Ferdinand, only reached mass production in 1947. By that time, production of the IS-3 not only started, but also ended, netting a total of 1555 tanks.

The IS-4 was already yesterday's news in 1945. In the winter of 1945, the design of a new tank began, the IS-7. This designation, as well as the index "Object 260", covered three tanks that were significantly different in their design and characteristics. Designed as a counter to the German Maus, the IS-7 was the most perfect fighting machine of its class. The characteristics of the tank that was finalized in 1948 boggle the mind even today: with a mass of 68 tons, it could reach a speed of 60 kph, all with the armament and protection no less than that of the 189 ton German monster, even superior in some regards.

However, the increasing mass was a trap for heavy tanks. ChKZ managed to produce the IS-4 with great difficulty: only 55 tanks in 1947 and 155 more in 1948. The IS-7 was even more problematic: it needed a new engine, the production of which was yet to be mastered. The 68 ton weight meant that new recovery vehicles were needed, and the tactical mobility of the tank was questionable. Few bridges, even railroad ones, could carry such a monster. There was also an issue with railroad platforms that could carry sufficient weight. The problems that were bypassed in one way or another in 1941 caught up. The same issues would have to be resolved if the KV-3, KV-4, or KV-5 reached mass production.

Weighing all pros and cons, Soviet leadership made the only correct choice. On February 18th, 1949, the Council of Ministers of the USSR had a meeting which included the commanders of the Armoured and Mechanized Forces, as well as representatives from GBTU. The result of the meeting was decree #701-270ss, which stopped the development and production of tanks heavier than 50 tons. The IS-7 was doomed, as was the IS-4 (the last 19 tanks were amde in 1949).

The same decree ordered SKB-2 of ChKZ and the experimental department of factory #100 (Chelyabinsk) to begin development of a new heavy tank, no more than 50 tons in weight. The design had to incorporate components from the IS-4 to speed up development. At the same time, the armour layout and hull design were to be taken from the IS-3, as the most appropriate for this weight. The design team had very limitd time: the first three tanks were to be ready in August of 1949, and another ten in September, for military trials. In total, only half a year was allotted to the production of a new tank, which was yet to be designed.

Working together

In order to solve such a difficult problem, two competing design bureaus were involved. On March 19th, 1949, the factory #100 design group was included in the newly created VNII-100 (Leningrad). The first task given to the institute was the design of the new heavy tank. J. Ya. Kotin headed this new team. Leningrad was tasked with development, and workers in Chelyabinsk put their designs into metal. 41 members of VNII-100 were sent to Chelyabinsk. The vehicle also got a Chelyabinsk index. Vehicles developed in Leningrad were designated Object 2##, whereas Chelyabinsk tanks were Object 7##. For example, the IS-4 was Object 701, and IS-7 was Object 260. This vehicle received the code 730, or Object 730.

Some sources claim that the Object 730 was based on the IS-4, but that, to put it lightly, is contestable. The IS-5 was effectively a new tank, only inheriting the V-12 engine from the IS-4, and, initially, the cooling system with two large fans. Otherwise, the vehicle that was designed in April of 1949 was the product of a completely different school. The IS-4, especially its hull and turret, was the product of 1943 technology. Since then, Chelyabinsk produced the IS-3, which had almost identical armour, and Leningrad produced the IS-7, which left the IS-4 far behind. Other components were greatly improved over the previous 5 years. A large amount of work was done on the suspension, transmission, and other components during the design of the IS-7. Additionally, as mentioned above, the development was mostly based in Leningrad, and the experience of local tank designers was fully applied to Object 730.

Looking closely, the IS-5 is a creative reformatting of the IS-7 mod. 1948. The front pike with driver's periscopes on the side, the rear with its characteristic slope, the V-shaped bottom of the hull and curved sides, all this indicates the heritage of the Object 730. The turret, a combination of IS-3 and IS-7 solutions, also has nothing in common with the IS-4. Since the mass of the IS-5 was limited to 50 tons, the armour had to be reduced for the first time since the KV-1S. Thanks to scientific work to increase the effectiveness of armour without thickening it, a series of solutions were implemented, making the tank more protected than the IS-3. Compared to the IS-4, and especially the IS-7, the protection of the tank decreased. Such was the cost for lowering its weight to 50 tons.

Another regression was seen in the armament. The D-25T, which was installed in the IS-2, IS-3, and IS-4, was already not enough for the military in 1944. The IS-7 received a new 130 mm S-70 gun, but it was not possible to install it in an IS-5. As a result, the IS-5 received the same D-25T. The armour and armament of the tank was closer to the end of WWII, rather than the end of the 1940s.

A tank of compromise

The Americans faced the same problem around the same time. Starting with the 64 ton T-29 Heavy Tank, American tank designers managed to develop a final tank weighing in at 65 tons. While Soviet tank designers were working on the 50 ton IS-5, their American colleagues were working on the T43 heavy tank with a 55 ton limit. As a result, the M103 Heavy Tank turned out to be slightly heavier at 56.7 tons, but this was still significantly lower than the 65 ton heavy tanks of the late 1940s.

The cost of weight reduction was weak armour. The turret suffered the most. A significant advantage of the American tank was its 120 mm gun, but this made the vehicle very large. The characteristics of the FV214 Conqueror were similar, but it turned out to be even heavier than the M103, 65 tons. One can say that all leading armies of the world made the same step back, but the Americans and British managed to improve the tank's armament. The cost was increased size, and therefore weight.

Even though the armament and armour were steps back, it would be wrong to consider the IS-5 a failure. For the late 1940s, armour that was completely immune to the German 88 mm gun was standard. The D-25T was equally modern, as its enemies weren't German tanks, but those of the former allies.

Even the M46 and M47 Patton tanks that appeared in the late 40s and early 50s were not proper adversaries for the IS-3, let alone the new tank. Until the 105 mm L7 gun began appearing in foreign tanks, the front armour of Soviet heavies was reliably impenetrable. By the way, trials of the IS-5 hull performed in May-June of 1950 showed that the front armour withstands hits from 122 mm shells at 100 meters. The Soviet Army received a modern heavy tank.

As mentioned above, many technical solutions migrated from the IS-7 to this tank. This includes the novel bundled torsion bars. This system allowed the length of the torsion bars to be drastically reduced. Other elements of the suspension (road wheels, idlers, tracks) were further improvements of IS-3 components. The suspension looked similar, but the design was drastically altered and reliability improved. It was designed in such a way that it could be installed on other IS series tanks without significant changes.

In the mid 1950s, IS-2, IS-3, and ISU vehicles were modernized. This meant that the new tank and the old tanks had identical suspensions. The use of a 750 hp V-12 engine allowed for superior mobility compared to the IS-3. The maximum speed increased to 42 kph. Several types of planetary transmissions were developed for the IS-5. It's worth mentioning that some components were tested on IS-4 and IS-7 vehicles lightened to 50 tons.

Preliminary blueprints were shown to the state commission in April of 1949. By June, working blueprints were complete. For several reasons, there was a delay, and the first hull only reached ChKZ on July 30th, and second on August 9th. The first IS-5 was finished on September 14th. The tank had a 6-step gearbox and planetary transmission from the IS-4. Trials showed that the transmission and cooling system do not last for the required 2000 km warranty period. As a result, an 8-step planetary transmission developed by VNII-100 was installed, a design with roots in the IS-7. Instead of a fan-based cooling system, an ejector system was used, like on the IS-7. Two more tanks were build in December of 1949, which participated in the winter trials.

Renaming

Trials requested by decree #701-270ss started with a half-year delay, in February of 1950. Three tanks were finished by April 5th and sent to Lomonosov, near Leningrad, where they underwent trials for the duration of April. Defects discovered during those trials were corrected by ChKZ, after which the tanks underwent more trials at Kubinka in October-November of 1950. Earlier, in June-July of 1950, the tanks underwent trials in Central Asia. In total, 13 IS-5 tanks were built in 1949-1950, and another 2 in 1951.

Changes were constantly made to the IS-5 to improve reliability. The tank served as a test bed for multiple systems, including an autoloader mechanism. The total sum of improvements was so great that it was decided that the tank should be renamed. In early 1953, the tank was named IS-8. This would be the name the tank would serve under, had Stalin not died on March 5th, 1953. In May, the tank was already referred to as only Object 730 in letters. It's possible that this was just a precaution to weather the power struggle in the Politbureau. On June 26th, L.P. Beria was arrested, and N.S. Khrushchev came into power.

The new heavy tank was accepted for service by a decree of the Council of Ministers on November 28th, 1953. This same decree assigned it the index T-10. The first 30 T-10s were built in 1954, and 190 tanks were built in the first series at ChKZ. Kotin's tank was the last to carry the name of a notable Soviet leader. 15 years prior, Kotin worked on the SMK heavy tank (Sergei Mironovich Kirov), which started the trend of naming heavy tanks instead of giving them numbers.

The T-10 was a temporary measure. In 1952, a program began to create a next generation tank, the result of which was the Object 777. The T-10 was destined to outlive its successor, which never moved past a scale model, as well as the next wave of heavy tanks, which birthed Objects 277, 279, and 770. In 1958, LKZ began production of T-10s, but only once did annual production surpass 200 units. In 1965, ChKZ built the last 60 T-10s, and that was the end for Soviet heavy tanks. A new type of tank appeared on the horizon, including the best parts of heavy and medium vehicles, the Main Battle Tank.

Original article by Yuri Pasholok.