In the first half of 1959, the design office of the Stalingrad Tractor Plant began work on the modernization of the tank PT-76B ("Object 740B"). Engineers under the leadership of S.A. Fedorov and Yu.M. Sorokin intended to rework the original project and improve the characteristics of the amphibious tank. It was assumed that the new tank "Object 907" will have higher mobility characteristics and will maintain firepower at the level of its predecessor. In addition, the new amphibious tank was planned to be equipped with several new systems.
To increase the level of protection, the tank "Object 907" received an armored body, which is a significantly modified units of the basic combat vehicle. It was proposed to assemble the forehead of the hull from several plates, the middle joint of which formed the characteristic “ship's nose”. In addition, instead of flat sides, the promising amphibious tank got curved. According to some sources, the thickness of the armor plates of the upgraded version of the PT-76B corresponded to the parameters of the body of the base machine: front sheets with a thickness of up to 80 mm and onboard to 10 mm. However, the modified shape of the case allowed a slightly higher level of protection. The design of the tower has not changed.
One of the main goals of the modernization project was to increase the mobility of the armored vehicle. For this, the “907 Object” received a forced B-6M engine with a power of 280 hp. Despite the increase in the tank's combat weight from 14 to 14,87 tons, a more powerful engine made it possible to maintain maximum speed while driving on the highway at the same level - up to 45 km / h. Old jet propulsion with a new engine allowed the new tank to reach speeds up to 11,2 km / h on the water. The tank received an additional tank, which made it possible to increase the fuel supply to 500 liters and increase the cruising range to 400 km.
The tank "Object 907" received a system of anti-nuclear protection. In this regard, a special air intake on the roof of the fighting compartment was provided for air supply to the engine to bypass the habitable volume. On a sheet, inside the fighting compartment, a supercharger was placed to create excessive pressure in manned volumes.
Weapon tank "Object 907" was completely borrowed from the base combat vehicle. The tower housed 76-mm rifled gun D-56TS with stabilization in the vertical plane and coaxial machine gun 7,62-mm. Ammunition guns remained the same - 40 shells. The gunner received a telescopic sight TSHK-66. For shooting at night, the gunner could use the TPN-1 sight with the L-2 searchlight. The tank commander could monitor the situation with the help of the combined device TKN-2 from the illuminator OU-3.
In August, 1959, the Stalingrad Tractor Plant, together with the shipyard No. XXUMX, built the first prototype of the amphibious tank, the 9264 Object. The running and fire tests of the experimental machine, which took place in 907, did not reveal any serious advantages over the base PT-1960B. Then a new tank was tested on the water, after which it was decided to close the project. The prototype of the tank "Object 76" showed insufficient stability at all speeds on the water. Moreover, during acceleration to maximum speed (even when using wave deflectors), the front part of the body burst into the water. Thus, all changes in the design of the hull, which seemed to help improve the motion characteristics of the machine afloat, did not yield any positive results.
Due to the absence of noticeable positive differences from the existing tanks and the presence of problems when moving on the water, the project “Object 907” was closed for hopelessness. The only prototype built is currently stored in the Museum of armored vehicles in Kubinka, near Moscow.
Despite the smaller number in the designation, the project "Object 906" appeared a little later than the tank with the letters "907". In 1960, the design team of the OKB Stalingrad Tractor Plant, under the direction of I.V. Gavalova and Yu.V. Shadrina began a project to upgrade the tank PT-76B, whose goal was to significantly increase firepower. In a number of sources, the 906 Object project is referred to as PT-85.
Tank "Object 906" was a modernization of the base PT-76B using a number of new units. In this case, most of the design remained the same. Great changes undergone the power plant of the tank. On the first prototype of the PT-85, the 8D-BM diesel engine with the HP 300 power was used. The following five tanks of the experimental series were equipped with EGD-20 engines of the same power. Due to all the changes, the combat mass of the “Object 906” tank reached 15 tons, but the powerful engine made it possible to reach a maximum speed on the highway about 75 km / h. On the water, the amphibious tank could accelerate to 10 km / h.
In the modified turret base machine installed new weapons. It was proposed to raise the firepower of the amphibious tank with the X-NUMX-mm D-85 rifled gun. In one installation with a gun mounted machine gun SGMT. The turret weapon was equipped with a two-plane Zvezda stabilizer. The stabilizer made it possible to point a weapon in a horizontal plane at a speed of up to 58 ° per second, in a vertical plane up to 20 °. The same system was responsible for turning the turret during commander target designation and removing the gun to a neutral position in the vertical plane for loading.
An interesting feature of the “Object 906” project was the loading mechanism located in the new aft niche of the tower. In laying the mechanism managed to place 15 shells. The total tank ammunition equaled 40 shells. When firing projectiles of the same type, the rate of fire could reach 14 rounds per minute. When using different ammunition, the rate of fire was reduced to 7-9 shots per minute. The loading mechanism was controlled by a remote control at the gunner’s workplace.
It was assumed that the standard tank ammunition PT-85 will be 8 armor-piercing and 32 high-explosive fragmentation projectiles. When fired from a distance of 1 km, an armor-piercing projectile, having an initial speed of about 1000 m / s, could penetrate an armor plate with a thickness of 185 mm. The maximum range of high-explosive fragmentation projectile reached 13,5 km. Such characteristics of the X-NUMX D-58 gun made the new amphibious tank a great advantage over the existing PT-85B caliber. Interestingly, the design of a floating tank based on a PT-76B equipped with an 76-mm gun was being worked out, but it remained in the early stages of design.
Sighting equipment, observation devices, etc. the equipment of the “Object 906” tank in most cases corresponded to the aggregates of the base machine PT-76B. According to some sources, the composition of the equipment of different prototypes differed from each other.
In 1961, the city of Stalingrad received a new name, and soon after that a new name appeared at the tractor factory. Now the Volgograd Tractor Plant in 1961 and 1962 has built six prototypes of the tank “Object 906”. From each other, they differed power plant and some items of equipment. Two prototypes were used in tests that took place in the first half of 1963, at the NIIBT test site. Despite a noticeable increase in fire performance, the upgraded amphibious tank with an 85-mm gun did not interest the military. The reason for this was the combination of technical, tactical and technological features of the project. The tank "Object 906" / PT-85 was not adopted, which, in particular, did not receive the continuation of the design of a floating tank with an 90-mm gun. So far, only one of the six prototypes of the “906 Object”, now in the museum of armored vehicles in Kubinka, has been preserved.
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