In the late forties of the last century, the IS-7 heavy tank was created in the Soviet Union. It had excellent armament for its time and solid armor. However, a number of circumstances associated with the emergence of new armor-piercing ammunition and the peculiarities of the country's road network led to the closure of the project. The IS-7 was never accepted into service. At the same time, the chassis of the heavy IS-7 earned a number of positive reviews and some representatives of the country's military leadership were in no hurry to abandon it. And the 130mm cannon was quite a tidbit.
In this regard, in 1950, the designers of the Leningrad Kirov Plant were given the task to create a heavy self-propelled artillery unit on the basis of the IS-7 tank. The project received the designation "Object 263", and V. S. Starovoitov. Initially, three versions of the new self-propelled gun were created, differing from each other in some design nuances. In the course of work on the "Object 263", these options often "exchanged" various design nuances, and as a result, only one version remained in the program, which was predicted to have a great future.
Since one of the main requirements for the new ACS was maximum unification with the IS-7 tank, its chassis was borrowed practically unchanged. The power transmission group remained the same: a 12-cylinder V-shaped diesel M-50T with a capacity of 1,050 horsepower and a six-speed gearbox. The same can be said for the suspension, rollers and tracks. At the same time, the overall layout of the hull has been significantly adjusted. The self-propelled armored wheelhouse was supposed to be located in the rear of the hull, so the engine and transmission were moved to the front. The fuel tanks, in turn, were now located in the middle of the armored hull. The change in the centering of the vehicle associated with the rearrangement was compensated for by an increase in the thickness of the armor. First of all, the forehead of the Object 263 should be noted. Unlike the forehead of the IS-7 tank, it was not made according to the "pike nose" system, but was a simple combination of rectilinear panels. The main advantage of the location of the armor panels at an angle to each other is the increase in the level of protection in comparison with the "straight" one. For this reason, it was proposed to equip the "Object 263" with a frontal sheet 300 millimeters thick. The sides of the hull in the project were much thinner, from 70 to 90 mm. As for the armored cabin, it also had solid protection: a frontal sheet of 250 mm and sides of 70 mm. With such armor, the "Object 263" could withstand shelling from all existing medium tank guns and a number of more serious guns.
The main armament of the Object 263 self-propelled artillery mount was to be the S-70A cannon. In fact, this was a further development of the S-70 cannon intended for the IS-7 tank. This project, created at the Central Artillery Design Bureau under the leadership of V. G. Grabin goes back to the pre-revolutionary B-7 naval cannon of 130 mm caliber. It is worth noting that in the course of several deep modernizations, the design of the gun was significantly changed and the S-70A had almost nothing in common with the original B-7 besides the caliber. The S-70A cannon had a solid size, caused primarily by a 57.2 caliber barrel. In addition, the breech and recoil devices were considerable. Because of this, the layout of the wheelhouse turned out to be rather unusual. The breech of the cannon almost reached the rear wall of the wheelhouse. For this reason, the latter had to be made folding. It was assumed that before the start of the battle, the crew would lower this part and be able to work without fear of damage to the wheelhouse. In addition, the folded back sheet slightly increased the floor area of the fighting compartment, which could slightly facilitate the work of the crew.
The 130mm cannon had a very high recoil. Therefore, a folding support device, reminiscent of a dozer blade, had to be added to the muzzle brake of the slot system and the recoil devices. On the available photographs of the "Object 263" model, it can be seen that in the extreme lower position it was holding on itself the lowered stern leaf of the deckhouse. Ammunition holders were placed along the sides of the wheelhouse, on their inner side. Separate loading shots were secured by seven from each side. For convenience, the shells were located in one holder, the shells in the other. Loading the gun was the responsibility of two crew members: the loader and his assistant.
All in all, the crew of the ACS "Object 263" was supposed to include five people: the commander, the driver, the gunner, and two loaders. For direct fire, the crew had a TP-47 sight, and for firing from closed positions, it was proposed to equip the self-propelled gun with a TSh-46 sight. The estimated rate of fire of the "Object 263" was not high - the crew could manage to make no more than one or one and a half shots per minute. The main reason for this was the specific layout of the wheelhouse, which did not allow achieving the same performance as the IS-7 tank (about six rounds). The low rate of fire, according to the military and the developers, had to be compensated for by the high fire characteristics of the long-barreled gun. So, from a distance of two thousand meters, the S-70A gun, when using the BR-482 armor-piercing projectile, had to penetrate up to 160-170 millimeters of homogeneous armor (at a meeting angle of 90 °).
At the beginning of 1951, the draft design of the new self-propelled gun was ready, and it was presented to the commission of the Ministry of Defense. The military authorities got acquainted with the work of the LKZ designers, after which the assembly of the full-scale model of the ACS began. On the layout, it was planned to test some ideas and identify layout problems, ergonomics, etc. Just a few weeks after the completion of the assembly of the "Object 263" model, an order came from Moscow: to stop the work on the project. Of course, the 130mm gun was a very good argument on the battlefield. However, the estimated weight of the new SPG was 60 tons. This was 8,000 kilograms less than the recently closed IS-7 project, but still too much for practical use in the current conditions. The design of the self-propelled gun, in theory, could be facilitated. But only at the cost of reducing the level of protection, which would not be the most reasonable solution. Based on the combination of advantages and disadvantages, the Main Armored Directorate decided that the Soviet army did not need such equipment. The only built model of "Object 263" was dismantled, but it never came to construction "in metal".
