IS-7 - history and development

Author: Viktor Kitov (EU forum)
Published and slightly redacted by: Silentstalker

Today, we have a guest article here by Vikto Kitov about the IS-7. Enjoy!

In the spring of 1944 after  lifting the siege of Leningrad at the Kirov plant which was partially destroyed, it was decided to manufacture the ISU-152 self-propelled artillery. Tank designers were returning to the Experimental Plant № 100, after the evacuation. The leader of the team was chosen to be J. Kotin. Under his leadership, the development of a new heavy tank which was to be well armed and heavily heavy armored. Itreceived the factory designation "Object 260", and later - the index "IS-7"

-A wooden model of the IS-7-

The high level of protection of IS-7 was provided not only by an increase in the thickness of armor plates, but also due to their significant slope. The form of the front was similar to the IS-3 - "pike nose," with somewhat smoothed contours. The mass of IS-7 reached 68 tons, to ensure adequate mobility it was needed to increase the capacity of the engine. It was planned to install two diesel V-11 or B-16 with a total capacity of 1200 hp, using an electric drivetrain similar to the tried and tested on the prototype tank IS-6 ("Object 253"). However, before making the first prototype of the IS-7 the design was canceled and only a full sized wooden mock-up was build. In 1946 work on the second version started. In the same year it was decided to build two prototypes. The lead designer of the machine was engineer G. Efimov, and overall management was done by A. Ermolaev. A second version of the IS-7 would be created, rather diffrent from its predecessor.

-Engine-

Since work on the B-16 engine failed. The TD-30 diesel engine was installed, developed  on the ACh-300 aircraft engine. Instead of an electric transmission a traditional mechanical one was used. A serial V 12-cylinder diesel engine M-50 1050 hp at 1850 RPM was installed (used on fast offshore boats). The TH-30 aircraft engine established on the basis of ACH-300, revealed a number of significant drawbacks during the tests. The M-50 engine was distinguished by its rather large dimensions, requiring new design solutions for its installation in the tank without increasing the height of the housing. They had to develop a new short torsion suspension (so-called "beams"), consisting of seven thin rods, and such that was enough space for the engine crankcase. The case height of 2426 mm was even lower than the 300 mm on the IS-2, and 24 mm lower then the IS-3.

-Engine specifications-

Engine Type: M-50T

Manufacturer: Plant № 800
Brand: M-50T
Type: Diesel
Volume: 62,400 cm3
Maximum power: 772 kW (1050 hp) at 1850 rev / min
Maximum torque: 4606 Nm
Configuration: V12 Cylinders: 12
Bore: 180 mm Stroke: 209.8mm
Degree of compression: 13.5
Cooling: Liquid
Stroke(number of cycles): 4
Recommended fuel: DL, DZ, DA

Speed​​  60 kp/h; Cross-country speed 32 kp/h
Range- 300 km
HP per tone- 15.4
Suspension- Individual torsion
Ground pressure kgf / cm ² 0,97
Fire fighting equipment with automatic thermo sensors which activate at 100-110 ° C


-Transmission-

The transmission for the tank was designed in two versions. The first, which was manufactured and tested in the IS-7, was a six-speed manual shift with synchronizers. Turning mechanism - a planetary, a two-step. Steering was done via a hydraulic servo.Tests showed good traction transmission quality, ensuring high average speed of the tank. The second version of the manual transmission had been developed in conjunction with the Bauman Moscow Higher Technical School.It was a planetary, 8-speed. Steering was done by hydraulic actuators with progressive gears. For the first time in the soviet tank design tracks were made with rubber-metallic hinges, hydraulic double acting shock absorbers, road wheels with internal shock absorbers operating at high loads and torsion beams.

-Electric Drive planned for the IS-6-

The first copy of the prototype was ready on September 8, the second - December 25, 1946. On field tests they showed remarkable speed for such machines- 60 km/h maximum speed and an average speed on rough road was 32 km/h. None of the heavy tanks of that time could boast with such high-speed characteristics.

Throughout 1947 in parallel with the long trials of the first two IS-7s work started on the creation of the next - better - option.

Increased armour and slope for the hull and turret after firing 88-mm, 122 mm and 128-mm shells at the prototypes on the NIIBT site at the Izhora factory. The thickness of the frontal plate was increased to 150 mm, placing them under  vertical angles of 50 ° - 52 °. The turret was given a less vulnerable form - it became more rounded, the thickness of the front was adjusted to 240 - 350 mm at an angle of 45 ° - 0 °, the side plates - to 185 - 240 mm at angles of 30 ° - 45 °. Even the most powerfull guns existing at that time (128-mm and 130-mm armor-piercing projectiles) failed to penetrate the armour.

-Crew-
The crew of the IS-7 consisted of five men and four of them were placed in the turret:

Commander - Right
Gunner - Left
Two Loaders - In the back, they also operated the machine guns.
The Driver was the only one to be located in the hull.


-Armament-

The first prototype was armed with a 130-mm S-26 gun. It used separate-case ammunition, the mass of the projectile was 33 kg. To increase the rate and ease the work of the crew a pneumatic loading mechanism was installed, developed in conjunction with the Institute of artillery.

The next version of the IS-7, was armed with a new 130-mm naval gun S-70 (7020mm long) a 54 caliber barrel and it's weight was 4225kg. The shell had a mass of 33.4 kg and an initial velocity of 900 m/s with the ability to punch through 163-mm armor, mounted at an angle of 30 °, at a distance of 1000m and 143 mm - 2,000m. Rare of fire was from 6 to 8 shots per minute thanks to the naval style "rammer" (Unconfirmed)

-S-70 Penеtration values-

Shell \ Distance--------------------------------->500---1000---1500----2000---3000 (m)
БР-482 (Angle of impact 30°)----------------->205-----195-----185----175------145 (mm)
БР-482 (Angle of impact 90°)----------------->250-----240-----225----210------180 (mm)

Keep in mind that at different times and in different countries, different methods for determining armor penetration were used. As a consequence, a direct comparison with similar data from other sources is often impossible or incorrect

-Details about the IS-7s guns-

Ammunition for the S-70 consisted of 30 shells. Rather then the bulky pneumatic loading mechanism that was used on the first machine, a smaller chain mechanism with the electric drive was developed. The characteristic difference between guns was the muzzle brake design: The C-70 used small holes, and a C-26 has a slot design.

The tank fire control unit  provided guidance, regardless of the position of the gun and fired automaticly as soon as there was a target lock. The number of machine guns on the IS-7 reached eight: Two - large caliber, and the rest - 7.62 mm RP-46. A second CPV-44 was aded on the roof of the turret for firing at air and ground targets. Aditionally two 7.62 mm machine guns and a 14.5mm were mounted in the gun mantlet. All of them had a remote control. Ammunition for the machine guns consisted of: 400 rounds of ammunition for the CPV and 2500 for the ER.

-The End-

During 1948 LKZ produced four prototypes of the new IS-7.

Following the factory tests they were handed over to the state. Chairman of the State Commission was appointed Major-General A. Owl. The main test of the Ministry of Transport Engineering of the USSR E. Kulchitsky well remembered these trials: "I was honored, I was asked first to give this remarkable machine"...With speeds exceeding 60 km/h, this heavy machine is easy to respond to the slightest force applied to the levers and pedals.The machine is totally submissive to the driver."
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During a test run one of the tanks caught on fire after exeeding the period for the trials. The automatic fire extinguishing system activated twice, but the fire could not be contained. The crew had to leave the tank, and it was completely destroyed. The plastic fuel tanks, which the designers installed instead of the normal metal ones to save weight, turned out to be the source for an additional fire hazard.

Despite the outstanding performance, the IS-7 failed to receive the approval of the State Commission.

In addition to a number of failures during the test, a negative opinion of the commission affected, first and foremost, it is was too heavy. The attempt to provide the highest level of protection brought the machine to a record 68 tons - instead of the planned 65.5 tons.

The "Object 260" was not accepted for service. However, in the course of the project designers  accumulated experience, and in the later types of Soviet tanks you can see many of the tried and tested to IS-7 components.

-Why?-

A definite negative role in the fate of the IS-7 played another heavy tank -the 60-ton IS-4, developed and put into production at the CHKZ in 1947, after the cessation of production of IS-3. The IS-4, at the time of its creation, had the most best armor, but the  transmission wasnt reliable. It was armed with the same guns as the IS-2 and IS-3. The biggest drawback of the IS-4 was the fact that its mass was greater than the capacity of railway platforms, and highway bridges simply couldnt withstand its weight. As a result the IS-4 effectively discredited the idea of ​​a tank weighing 60 tons, which caused the skepticism of military experts regarding the IS-7.

Another explanation for the rejection of the IS-7 is that at that time the concept of increasing the role of tanks in a probable nuclear war, called for an early deployment of a large number of armored units, and thus to produce the greatest possible number of tanks in peacetime.

Blueprints and comparison

The last IS-7 (Model 1948) is in the Museum's collection of armored vehicles in Kubinka.