IS-M (Shashmurin)

Soviet Union (1944)
Heavy Tank – Drawings Only

Just months after the IS-2 began production, work began on developing a new heavy tank to replace it down the line. Engineer N. F. Shashmurin and his team envisioned an unusual tank, meant as a direct IS-2 upgrade, the IS-M. The most notable aspects of Shashmurin’s design were the large-diameter road wheels and the rear mounted turret. However, his project was not taken into consideration and was short-lived, although it did pave the way to the IS-6, which used some of its features.

Shashmurin and the IS

Tank designers are usually overlooked in the popular imagination, and those few acknowledged are usually limited to the likes of Ferdinand Porsche or Alexander A. Morozov. Even when limited to Soviet heavy tanks, the names of Nikolai L. Dukhov and Joseph Y. Kotin overshadow the others. Yet Nikolai Fedorovich Shashmurin was the man behind the creation of one of the USSR’s greatest war-winning tanks, the IS-2.

Born in 1910 in what at the time was called St. Petersburg (to be renamed Leningrad in 1924), Nikolai Fedorovich Shashmurin started his engineering studies at the Leningrad Polytechnic Institute in 1930 and graduated in 1936. By 1937, he had started to work at LKZ (Leningrad Kirov Plant) as an engineer for the SKB-2 design bureau. Before the war, he would work on the T-28 medium tank and create the torsion bar suspension system (T-28 No.1552) fitted on the SMK and U-0 (first KV-1 prototype), a system which would be implemented further on all future Soviet heavy tanks and self-propelled guns. Additionally, he developed gearboxes for the KV-1 (his gearbox would be dropped in favor of Dukhov’s infamous gearbox which would haunt the KV-1 for its entire service life), KV-220, KV-3, and even his own design for the KV-4 program.

With the beginning of the German siege of Leningrad in 1941, the LKZ (Leningrad Kirov Factory), specifically SKB-2 engineers, were evacuated to ChTZ (Chelyabinsk Tractor Plant) in Chelyabinsk (near the Ural Mountains), renamed ChKZ (Chelyabinsk Kirov Plant) a few weeks later. At Chelyabinsk, Shashmurin would develop the gearbox of the KV-1S and, after N. V. Tseits’ death in summer 1942, he became the head engineer for the KV-13 (at the time called IS-1), a vehicle which he did not like. Nonetheless, he would build upon it, and by May 1943, he had designed a new variant, equipped with an 85 mm D-5T gun specifically for the task of penetrating the German Tiger I, mated to a new hull. This was the Object 237 (at the time named IS-3), which would be adopted in service in September 1943 as the IS.

In parallel, Shashmurin designed the Object 238, meant to fit the new 85 mm S-31 gun in the KV-1S, but it was unsuccessful due to the cramped conditions within the turret. Production of the IS-1 started in November of that year, but it would not last long, as, by May 1943, work began on fitting the IS with the 122 mm D-25T gun, and by December 1943, the Object 240 would enter service as the IS-2. The mounting of such a powerful high-caliber gun was unprecedented in Soviet heavy tanks, which normally had similar, if not the same, guns as medium tanks.

Improving the IS-2

Extensive testing of the IS-2 was done at the NIBT (38th Research Test Institute of Armored Vehicle) proving grounds at Kubinka in January and February 1944, where it was concluded that the armor of the tank was not sufficient. Most notably, the “stepped” frontal hull was considered a weak spot, and it was proposed that the frontal hull should be made out of one angled plate.

Even after the first IS combat engagements, it became clear that, with the introduction of the German Panther tank, armed with a 75 mm KwK 42 L/70 (which could pierce the frontal armor of the IS heavy tanks) that the IS was insufficient. As early as September 1943, General Fedorenko (Head of the Armored Vehicle Directorate of the Red Army) would send a letter to Stalin, requesting the thickening of the IS armor and increasing its weight to 55-60 tonnes.

Additionally, in November 1943, the technical requirements for a new heavy tank were set by the GABTU (Main Directorate of Armored Forces). It was to have a mass of 55 tonnes, crew of 5, 160-200 mm of armor(frontal turret and hull), 800-1,000 hp engine, and a 122 or 152 mm gun. Speed was to be at least 35 km/h. These requirements would be laid down at the ChKZ plant on 3 December (10 December according to other sources) by factory director I.M. Saltzman.

The ChKZ SKB-2 design bureau, headed by N.L. Dukhov, had already worked on a new heavy tank since July, with its own funds. It was the 56-tonne K tank. The project was named Object 701.

However, on 21 March 1944, the GABTU changed the technical requirements. The weight was lowered to 55-56 tonnes, armament was a 122 mm gun with a muzzle velocity of 1,000 m/s, and 30 to 40 rounds had to be carried. The engine was to have a 1,000 hp output and allow for 40 km/h top speed. Armor thickness was not specified, instead, it was to be immune frontally to the Panther’s 75 mm KwK 42 L/70 and the 88 mm PaK 43/2 L/71 of the Ferdinand/Elefant.

These changes forced the reworking of the existing Object 701, but a green light was given the same month to produce 2 prototypes, leading to the IS-4 tank’s long development, with the first prototype, the Object 701-0, being built in May 1944.

At the same time as the developments at SKB-2, the other design institution at ChKZ, Factory No.100, also worked on their own tanks based on the same requirements. Headed by J.Y. Kotin, their approach was different to that of SKB-2. Instead of designing a new tank, they focused on a deep modernization based on the IS-2. By 18 April 1944, Factory No.100 would present its initial designs. Again, 2 models were built, one with a frontal plate separated into 3 parts (as on the first K tank) and one with a UFO-shaped hull, akin to the Object 279, designed and built decades later. Despite the increased protection, both variants had the same weight as the IS-2, 46 tonnes.

A document dated 8 April 1944, ordered J.Y. Kotin and his team to develop an upgraded variant of the IS-2 and subsequent SPGs over a 3-month period. The improvements should have included, but not been limited to, strengthened the armor protection, transmission, and chassis.

This would likely trigger the development of a new IS-2 modernisation, based on the requirements from 21 March. The design was to be less ‘radical’ and closer to the IS-2, but some very big changes were made. The tank would be called the breakthrough tank IS-M, the M standing for модернизация, meaning ‘modernisation’.

Sources do not agree exactly when development started, some arguing March, whereas others early April 1944. Nonetheless, N.F. Shashmurin was head of the project. While some design elements were taken from the previous upgraded designs, the main change was moving the turret to the rear of the hull, creating a very unique tank. A drawing of the tank would be made by Dobrovolsky. Who he was is so far unknown.

Design

The design of the IS-M was peculiar and unorthodox. The entire upper hull was made from several stamped steel plates, slightly angled inwards, with both the front and rear angled heavily. These were welded to the lower hull, which, while still mostly flat, had angled corners for extra weight saving. In addition to the main variant, a second variant was drawn out, with standard IS running gear. An SPG version was drawn as well, although only with very superficial details.

The IS-style turret was mounted at the rear of the hull, which allowed for very little gun overhang, decreasing the chance of the gun getting damaged in tight places such as forests and cities, or steep maneuvers, such as trenchcrossing. Despite its general shape being similar to the turret of the IS, several key components had been done away with, such as the big commander cupola or air vent.

Powerplant

The engine was to be an M-40 aviation engine, equipped with 4 TK-88 turbochargers. The displacement was of 61.07 l and had an output of 1,200 hp. Other sources claim it was a modified variant of the standard V-2-IS, such as the V-11 or V-16, yet these would only output between 500 and 700 hp, far less than the 800 to 1,000 hp specified. The M-40 engine was based on an aviation engine, thus could run on both diesel and kerosene. Whatever the engine was, it had a 10 h running time. The powerplant was kept inside an own compartment in the center of the hull, protecting the fighting compartiment and ammunition, consequently isolating the driver. Fuel tank was in the front, to the right of the driver. As the sprocket remained to the rear of the hull, the entire braking and final drive ensemble was kept at the rear, as on the original IS. However, this meant that the gearbox and driveshaft ran through the floor of the crew compartment. The transmission was likely offered in 2 variations, electromechanical, very similar to that on the Ferdinand/Elefant, or a conventional mechanical one. The gearbox was of planetary type.

For access to these components, the rear engine plate could be opened and rested on the hinges, for access to the final drive and brakes. The roof of the engine compartment was also removable, and had one engine access hatch, 4 air vents and 4 air purification filters.

Suspension

Two different running gear options were presented, one with 6 large-diameter road wheels, which allowed the returning track to rest on them, or 6 IS road wheels with 3 return rollers. The large road wheels would offer improved mobility over very muddy terrain, where smaller road wheels would clog up with mud. Additionally, they removed the need for return rollers. In turn, the standard IS wheel layout was already in use on various IS and KV series of tanks, resulting in a cheaper and smarter logistic choice. In both variations, the wheels were sprung by torsion bars.

Crew

The crew was larger than on the IS-2, with 5 men; a commander, gunner, loader, driver, and radio operator. The commander sat in the left corner of the turret. He had a low profile cupola equipped with 2 opposite facing periscopes for vision. Sat in front of him was the gunner, who operated the main gun. He had the main gun sight for vision and an extra, fully rotating periscope for a better field of view. Opposite him, to the right of the gun, sat the loader. He had to load the 2-part ammunition gun, as well as assist the commander in various tasks. For entry and exit, he had his own hatch with a periscope. The driver sat in the front of the hull, from where he would control the tank with 2 tillers. One direct vision slit in the armor was provided, as well as a fully rotating periscope. For ease of driving during the night and visibility during maneuvers, the tank had a single headlamp on the right side of the upper hull. The radio operator was likely seated to the driver’s right, also in the hull. He also had a rotating periscope for vision.

Armament

The exact armament of the IS-M was never specified, other than its caliber, 122 mm. However, considering the German-style muzzle brake, it was a D-25T, as on the standard IS-2. The tank was equipped with 40 shells for the main gun.

122 mm D-25T ammunition specifications
Shell type	APHE (BR-471)	APHE (BR-471B)	HE (OF-471)
Mass (kg)	25	25	25
Muzzle velocity (m/s)	795	795	800
Explosive	160 g	160 g	3.6 kg TNT
Penetration	200 mm	207 mm	42 mm (calculated)

Around the tank, 3 GVG 7.62 mm machine guns were mounted, one coaxial to the main gun, one in a ball-mount at the rear of the turret, and one in the frontal hull, which is not visible in the drawings. A ‘large caliber’ machine gun was to be added to the commander’s cupola for anti-aircraft purposes, likely a DhSK 12.7 mm machine gun, but it is not shown in the drawings either.

The SPG variant of the IS-M was likely armed with an 152.4 mm BL-8 gun, developed at the beginning of 1944 and tested during July of the same year on the ISU-152-1 (Object 246).

152 mm BL-8 ammunition specifications
Shell type	APHE (BR-540)	APHE (BR-540B)	HE (OF-540)
Mass (kg)	48.8	48.96	43.56
Muzzle velocity (m/s)	850	850	850
Explosive	0.66 g	480 g	5.86 kg TNT
Penetration	247 mm	276 mm

Armor

The frontal plate was a continuous flat plate of 200 mm angled at around 45°. Side armor was 160 mm thick and angled at 60° on the upper hull and flat on the lower hull. The rear was also heavily angled and 120 mm thick. The turret was 160 mm all around, but being awkwardly rounded, it increased its effectiveness significantly frontally. This gave the IS-M superior protection to any heavy tank of the time, while still maintaining a modest 55 tonnes weight.

Variants

In the background of the original drawing, 2 additional vehicles can be seen. The first is also an IS-M, but with a different set of running gear, namely 6 IS-style road wheels and 3 smaller return rollers. This was likely added as an alternative to the large roadwheel design.

Further back, a completely different vehicle is shown, a form of SPG based on the IS-M. The turret was replaced with a fixed casemate with a large 152 mm BL-8 gun. Interestingly, the running gear is the same as on the previously described IS-M.

Return to Leningrad and Further Developments

The IS-M was short-lived. Alongside its 2 earlier counterparts, all were abandoned in April 1944. Instead, Factory No.100 began work on a vehicle meant to rival the SKB-2’s Object 701 and thus become the new generation heavy tank. It would incorporate several features from both the IS-M and the 2 wooden mock-ups presented on 18 April 1944. This was the IS-6, designed at first in secrecy. Like on the IS-M, 2 variants were designed, one with large diameter road wheels and a steeply armored hull (Object 252). The second would use an electromechanical transmission on an IS-2 lower hull (Object 253).

In May, with the Soviets having lifted the Siege of Leningrad, the SKB-2 design bureau and Factory No.100 were moved back, and thus the LKZ was revamped. Many engineers moved back, including Shashmurin. Back in Leningrad, they would continue work on the IS-6. In August 1944, the Object 244 was used as a testbed for the Object 252’s wheels, first designed on the IS-M, and later the 122 mm D-30 gun. The Object 244 itself was a prototype dating back to February 1944, meant to test the new 85 mm D-5T-85BM on an unmodified IS-1 (Object 237). The project was named IS-3, although this has nothing to do with the later IS-3 heavy tank (Object 703). After a military representative from Factory No.100 reported the IS-6 secret development to the GABTU, it was ordered that further development and prototype production should take place at Uralmashzavod in Yekaterinburg, but without the end game of entering production.

Back at ChKZ, which had been working full-time on the Object 701, it was realized that it needed to present its own modernization of the IS-2. Thus, in August 1944, they presented the blueprints of an upgrade to the IS-2. At first glance, it looked like an unchanged IS-2, but it featured various improvements, such as refined frontal armor layout, thicker turret armor, improved turret design, and many mechanical changes, such as improved cooling system and engine room. Allegedly, one prototype was built. Yet, by October 1944, the project was abandoned in favor of a new tank, which incorporated many IS-2 features, but was still radically new. It was called the Kirovets-1 and given the Object 703 index. After several alterations, most notably the addition of its most famous feature, the legendary pike-nose, the IS-3 was born.

The pike-nose on the IS-3 was ‘borrowed’ from the IS-2U and Object 252U, an upgrade of the IS-2 and Object 252 meant to equip them with pike-noses. As a matter of fact, the IS-2U, designed in November 1944, was the last genuine attempt to fundamentally upgrade the IS-2 heavy tank. The IS-2 U’s turret was itself heavily inspired by earlier designs, such as the IS-M.

The IS-6 would end up unsatisfactory. The GABTU never intended to adopt it into service regardless. The Object 253 with the electromechanical transmission caught fire during testing. Both IS-6s were deemed insufficiently armored in comparison to the IS-4, and once the IS-3 was nearing production, the fate of the IS-6 was sealed.

Shashmurin himself, who had worked throughout the entire development of the IS-6, was never fond of the idea. Just like on the KV-13, he was a true believer in what he called “tank of maximum parameters” a tank which pushed the capabilities of the industry and designers to their limit, in an attempt to reach an unstoppable heavy tank. His first such vehicle was the IS-1 and later IS-2. For him, the IS-6 was a waste of time, especially considering the end of the war. As for the rivaling ChKZ heavy tanks, he had the following to say:

“We had finally created an almost perfect tank, capable of breaking through any enemy defenses. Ideal in its potential, all the qualities of the IS-2 could manifest themselves only in the development of the solutions found and tested in it. Alas, the improvement of the IS-2 was left to chance, and instead of developing already tested solutions, they began to invent new “bicycles”. An unjustified race began in the creation of independent models of heavy tanks, in many respects similar to the race that took place when creating the KV. The sad experience of the very recent past had taught us nothing…
The impressive, but unreliable IS-4 and IS-3 were being designed and created, another “monster” with two engines was being designed, a kind of electric locomotive was being built on tracks – a tank with an electromechanical transmission IS-6, which burned down after driving through the factory yard only 50 meters. In general, the design idea was in full swing, and in the meantime, the fighting was done by the “rude” workers of the IS-2, and not by the “handsome” IS-3, the production of which began in the early ‘45 and which immediately began to break down with the regularity of the sad memory of the KV-1.”

After the war, Shashmurin would finally fulfill his dream of designing a true “tank of maximum parameters”, the IS-7, which indeed, pushed the technology of the time to its limits, being the heaviest Soviet tank ever built, as well as several work on ATGM-based heavy tanks, PT-76 and more.

Conclusion

The IS-M itself was a short-lived design meant to offer an arguably unnecessary upgrade to the IS-2. It would incorporate some very interesting features and solutions, such as a rear mounted turret, large diameter road wheels, and a curved hull. It alo took in consideration several running gear designs and an SPG layout. Nonetheless, despite its short life, it was a crucial factor in the developmental progress of Soviet heavy tanks during the Second World War, by leading directly into the development of the IS-6, which lost in turn to the more refined, though still crude, IS-3 and IS-4 designed at ChKZ. For Shashmurin, the IS-M was certainly not his most prideful creation, but through its odd nature, it complements well the career of one of the USSR’s most important heavy tank designers of the Second World War.

IS-M specifications
Dimensions (L-W-H)	7 x 3.2 x 2.7 (m)/td>
Total Weight, Battle Ready	55 tonness
Crew	5
Propulsion	1,200 hp diesel (V12) M-40 with 4 turbochargers or 500-700 V series engines
Speed	40 km/h
Armament	122 mm D-25T 3x GVG machine guns 1 (?) DhSK machine gun
Armor	Turret: 160 mm (hull) front: 200 mm Sides: 160 mm Rear: 120 mm Roof and belly: 30 mm
Total Production	0, drawings only

Sources:

IS Tanks – Igor Zheltov, Alexander Sergeev, Ivan Pavlov, Mikhail Pavlov
Supertanki Stalina IS-7 – Maxim Kolomiets
Heavy Tank IS-4 – Maxim Kolomiets
Tank Power of the USSR – M. N. Svirin
Modest genius: who created the IS-2 tank, which became a symbol of Victory – Rossiyskaya Gazeta (rg.ru) – Sergey Ptichkin
Holes in the armor -Sergey Ptichkin, Sergey Zykov
Tank Archives: Modernization on Paper – Yuri Pasholok, Igor Zheltov, Kirill Kokhsarov
Tank Archives: Wrong Place, Wrong Time – Yuri Pasholok
IS-2: Struggle for the Assembly Line | Warspot.net – Yuri Pasholok
Not in the amplitude of the | Warspot.ru -Yuri Pasholok
Muzzle wedge for heavy tank | Yuriy Pasholok | Zen (dzen.ru) – Yuri Pasholok
Tank Archives: Improving the IS-2 – Peter Samsonov
“>Russian Heavy Tank Object 244 – The Original IS-3 (thedailybounce.net) -Harkonnen
IS-2Sh – unusual “Stalin” (voentex.ru)