The King of the IS Heavies - The IS-7 - Tank Historia

The King of the IS Heavies – The IS-7

Imagine a 75 ton machine that has better armor than a heavy tank, a better gun than a tank destroyer and the mobility of a medium tank. You may think this vehicle must be a modern main battle tank, but you’d be wrong. It is in fact the mighty IS-7 from the 1940s.

At the time of its creation the IS-7 was the most advanced tank in the world. It featured a complex armor layout, a 1,000 hp diesel engine, remote control machine guns and an autoloader.

The IS-7 has been popularised by the online game World of Tanks, where it is known for its virtually impenetrable turret. Surprisingly this isn’t too far from reality.

This is the real story of the IS family’s biggest and baddest.

Contents

IS-7 Background

The life of the IS-7 starts in 1945. The breakthrough tank, known at the time as Object 260, was conceived by Nikolai Fedorovich Shashmurin, the man behind the IS-2.

It followed on from the IS family of vehicles (standing for Iosif Stalin) and was in many ways the culmination of the best features the family had to offer.

The Soviet’s heavy tank family. Image by Marcus Burns CC BY 3.0

Right from the get-go the tank had to be able to withstand a direct hit from the German Jagdtiger’s 128 mm PaK 44 from a range of 1,000 meters. This weapon was used as a benchmark for many years after the war.

This requirement was achieved by a complex armor layout and good old fashioned thickness.

The IS-7’s Insane Armor

To hold up against the 128 mm PaK 44 the IS-7 had to be seriously tough. It used a similar armor layout to the IS-3, with a distinct “pike nose,” a rounded turret and well angled sides.

The pike nose was made up of two 150 mm thick armor plates angled at 65 degrees. The lower glacis plate was specified to be 100 mm thick, but actual measurements indicate the plate is between 100 and 120 mm.

The extremely thick and well-angled armor of the IS-7 made it virtually impervious to all Western tank guns at the time.

The sides of the hull are equally formidable and uniquely shaped. Looking at the IS-7 from the front, the hull resembles a wide “V”. The upper portion of the side armor is 150 mm thick, while the lower portion is 100 mm thick.

The 100 mm plate curves out to meet the 150 mm section, and this curve was formed by bending the entire plate in a press.

IS-7 armor thickness diagram.
This cross sectional view of the IS-7 shows the unique arrangement and massive thickness of its armor.

The turret is a smooth bowl-like shape that is extremely well protected. The gun mantlet is 350 mm thick, while the turret front is up to 250 mm thick angled at 50-60 degrees.

The insane armor protection of the IS-7 was enough to stop virtually any tank-mounted weapon at the time.

Firepower

Like the armor, the Soviets spared no expense when it came to firepower. The IS-7 was armed with the 130 mm S-70 gun and no less than eight machineguns.

The 7 meter long gun weighed over 4 tons.

Its 33.4 kg shell travelled at 900 m/s and could punch through around 175 mm of armor at 30 degrees from 2000 meters away. In a testament to its armor, the IS-7 was unable to penetrate itself frontally.

The IS-7’s 130 mm S-70 main armament was derived from a naval gun. Image by VORON SPb CC BY-SA 3.0

The gun fired two-piece ammunition, which was loaded by what is often referred to as an autoloader. In reality, the system was more of an automatic loading assist.

It was located in the rear of the turret and contained both the projectiles and charges. When cranking a handle, the mechanism dropped both the projectile and charge onto a conveyor belt that fed into the gun’s breech. When in the correct position, the two parts would be rammed in and the conveyor would move out the way of the gun.

The loading assist mechanism a the rear of the IS-7’s turret. Image courtesy of World of Tanks North America’s YouTube channel.

With this system the IS-7 could reportedly fire 6 to 8 rounds per minute.

In terms of “lighter” weapons, the IS-7 was literally bristling with machineguns. Two forward-firing 7.62 mm machineguns were positioned towards the rear of the tank in armored boxes, one on each side. They were fixed in place and operated by the driver.

Note the 14.5 mm machine guns on the turret roof and above the main gun. Also, the 7.62 machine guns at rear of the turret and hull can be seen. Image by Uwe Brodrecht CC BY-SA 2.0.

The turret also had two fixed 7.62 mm machineguns, this time facing towards the rear of the tank and operated by one of the two loaders. The main gun was accompanied by three – yes three – coaxial machineguns. Two 7.62 mms and one 14.5 mm.

Finally, another 14.5 mm machinegun was positioned on the roof for anti-aircraft work.

The practical use of these guns has been questioned, and some would have likely been omitted on production variants.

The IS-7’s Excellent Mobility

With so many weapons and armor that simply laughed at Western weapons, the IS-7 came in at a rather portly 75 tons (the heaviest Soviet heavy tank ever).

You’d be forgiven for expecting the IS-7 to be horrifically slow, but this is certainly not the case.

To counter this monster’s weight the Soviets chucked in a 62 litre 1,050 hp M-50T marine diesel engine. This gave the tank an impressive power-to-weight ratio of 14 hp per ton (better than a Sherman) and a top speed of 33 mph (60 km/h).

The tank no longer utilised the classic Soviet method of keeping track pins in place by simply banging them back in with a metal wedge.

The driver controlled the tank through an 8-speed planetary gearbox. It was hydraulically assisted and test drivers noted it was a breeze to operate and allowed for extremely precise movements.

Even the tracks were special, with the IS-7 being one of the first Soviet tanks to use rubber bushings and pins retained by bolts.

Demise

The IS-7 proved to be an excellent vehicle during testing, and had very few, if any, major problems (it was never put through combat though, so its true capabilities will never be known). It was easy to drive, very mobile, carried an immensely powerful gun, had a good rate of fire and carried some of the most formidable armor ever put on a heavy tank.

Despite all of this, the IS-7 was cancelled in 1949. The official reason for its cancellation is unknown.

Although visually similar, the T-10 was simpler and therefore cheaper. Image by Gutsul CC BY-SA 3.0

The IS-7’s cost, complexity and its weight in particular were likely major factors. Additionally, with WWII safely in the past, the Soviets had little use for a vehicle with such capabilities.

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Finally, tanks like the T-10 could do most of the IS-7’s job at a much lower price.

Only 6 IS-7 prototypes were built, with a single one surviving at the Kubinka Tank Museum in Russia.