IS-3 Heavy Tank - Design
The general layout of the IS-3 tank was traditional - the main parts of the tank were a turret and a hull with a chassis. The hull and turret housed the mechanisms and components necessary for the normal operation of the tank, as well as space for the crew members.The cast IS-3 turret had a very perfect shape for that time - a flattened hemisphere, with a large wall thickness, a gun mask was very successfully inscribed in it. Thanks to the use of a turret of this shape, the IS-3 became 280 mm lower than the IS-2, which significantly reduced its visibility on the battlefield. To ensure a high speed of aiming the gun at the target, the controls for the tank turret were duplicated in the places of the gunner and the tank commander. The general disadvantages of the IS-3 tank include the high labor intensity of its manufacture (the cost of one vehicle was 350,000 rubles), the tightness in the fighting compartment - the internal volume of the vehicle was only 11.6 m3, and the low rate of fire of the D-25T gun, which had separate loading.
Compared to the IS-2 tank, the new vehicle had the following differences. Its hull was completely welded from rolled armor plates and did not have cast armor parts, while the bottom had a trough-like shape, and the sides were composite (from the lower and upper vertical parts welded together). The selection of the thicknesses and angles of inclination of the armor plates of the hull made it practically invulnerable to all calibers of enemy tank and anti-tank artillery. The main feature of the project was the flattened turret, developed by the designer G.V. Kruchenykh. The large angles of inclination of its walls contributed to the ricochet of enemy shells, and the rational internal layout made it possible to significantly increase the thickness of its booking without an excessive increase in mass (compared to the IS-2 turret). The new turret was shaped like a spherical segment and was cast in a single piece. The thickness of the armor of the sides in its front part (near the gun mask) reached 360 mm, and in other directions it was at least 160 mm, the roof - 30 mm. The armament of the tank remained the same - the 122 mm D-25 tank gun. Small changes were made to the design of the tank's transmission to improve the reliability of its operation.
Inside, the hull of the tank was divided by a metal partition into a fighting compartment with a command post and a power compartment. The control post was a driver's seat, which was located along the longitudinal axis of the machine. Above it there was a triangular hatch with a lid sliding to the side, located on the roof of the hull in front of the turret. A viewing device was installed in the hatch cover, providing the driver with an external view. Before opening the hatch, it had to be removed. Next to the driver's seat were the tank controls and instrumentation. And behind it, in the bottom of the tank, there was an emergency hatch, and stores with cartridges for a machine gun were also stored here.
In the middle part of the tank hull (behind the control compartment and in the turret) there was a fighting compartment. The fighting compartment housed: the seats of the loader, the gun commander and the tank commander, the main part of the ammunition and part of the spare parts. In the metal partition between the fighting and power compartments, there were several hatches and openings to facilitate access to the engine components.
The cast turret had a flattened spherical shape. In the roof of the turret there was a large oval hatch, closed by two covers. The loader's observation device (MK-4) was installed in the right cover, and the commander's observation hatch was located in the left cover, closed with a round rotating cover, in which the commander's observation device was mounted (MK-4 with a turret rotation control button). This device was intended for observing the terrain, determining the range to the target, for targeting and adjusting artillery fire. The IS-3 did not have a developed commander's cupola. This design decision is difficult to explain, since by the time the IS-3 was being designed, all Soviet tanks already had a commander's cupola, the need for which for the commander to fully observe the battlefield had become generally recognized. Practice has shown
A 122 mm tank gun and a 7.62 mm DT machine gun paired with it were installed in the cast turret mask. In addition to the cannon, the turret contained ammunition (shells) and a radio station, which was maintained by the tank commander. The shells were placed in the turret in special trays (25 shells). On the right side of the gun, there was also a stack of five shells. The maximum turret traverse speed was 12 ° / s. The electric swing drive was equipped with a command control system: the commander could, while holding the target in the field of view of his viewing device, press the button and turn the turret in a given direction along the shortest path. When the line of sight coincided with the axis of the bore, the turret stopped. The gunner carried out vertical aiming of the gun at the target using a manual mechanism.
The main armament of the tank was a 122-mm D-25T cannon, model 1943, with a barrel length of 48 calibers. The gun was equipped with a two-chamber muzzle brake and a horizontal wedge breech with a semiautomatic mechanical type. The practical rate of fire was 2-3 rounds per minute, and the direct-fire range was 1100 meters. The gun's ammunition consisted of 28 separate loading rounds: 18 high-explosive fragmentation and 10 armor-piercing rounds. To facilitate the work of the loading stacks, designed to accommodate armor-piercing shells, were painted black, and the rest in steel gray. For the cannon, separate loading ammunition was used (high-explosive fragmentation OF471 and OF-471N, armor-piercing B-471, BR-471 and BR-471B). Projectile weight - 25 kg, muzzle velocity - 781 m / s. From a distance of 1000 meters, an armor-piercing projectile pierced armor with a thickness of 150 mm.
To combat air targets, a large-caliber 12.7-mm DShK machine gun of the 1938 model or the DShKM machine gun of the 1938/1944 model (designed by Degtyarev and Shpagin) was installed on the roof of the turret. The machine gun was fired using a K8-T collimator sight, which provides aimed fire at targets moving at a speed of 400 km / h at an altitude of 400 m. The ammunition for the machine gun was 250 rounds. Chassis A V-11-IS-3 diesel engine was installed in the power section, along with auxiliary devices (lubrication, power and cooling systems). The V-11-IS-3 engine was a twelve-cylinder four-stroke liquid-cooled diesel engine with a maximum power of 520 hp. and was, in essence, an improved V-2K engine.
In the engine compartment, four main box-shaped fuel tanks were installed: two tanks to the left of the engine and two to the right (as left and right groups), the total capacity of which was 450 liters. At the stern were attached four additional cylindrical fuel tanks included in the power system. The capacity of each tank was 90 liters. Additional fuel tanks made it difficult to turn the turret, so, if necessary, the crew could drop them without leaving the car.
However, despite its formidable appearance, already at the very beginning of operation in the troops, the IS-3 showed a number of shortcomings, which were the result of design miscalculations and mistakes made in the course of its design. The fruit of the joint work of the designers of ChKZ and Experimental Plant No. 100 confirmed this proverb. For example, the hasty design of the main part of the tank - the IS-3 armored hull - led to the fact that its design, providing a very high level of projectile resistance, did not have the required operational rigidity.
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