The transition of the Red Army to active offensive operations at the end of 1942 demonstrated the need to equip it with mobile artillery of special power. To combat powerful bunkers and destroy fortified buildings during urban battles, sometimes even towed artillery systems of 152, 4 mm caliber were not enough. To solve such problems, the Red Army had a towed howitzer B-4 mod. 1931, but its advance to position for direct fire was very dangerous for the gun, crew and tractor. In addition, the low speed of movement of the B-4 on the march did not allow the use of the howitzer during quick and deep strikes directed deep into the enemy's defenses.
Guided by these considerations, already in 1942, the USSR prepared a draft design for the placement of the B-4 howitzer on a fully armored self-propelled gun belonging to the class of assault guns. The self-propelled gun was planned to be created on the basis of the KV-1 tank, this project was designated U-19. The design weight of the developed vehicle was 60 tons, which became an unbearable burden for the already overloaded and unreliable transmission of the KV-1 heavy tank. The second limitation of such an ACS was the small elevation angle of the howitzer, which did not allow the use of its ability to conduct mounted fire at maximum range from closed positions. The project was canceled.
In the fall of 1943, GAU again returned to the idea of creating an ACS of large and especially high power. The main armament of the self-propelled artillery unit was to be a 203-mm howitzer mod. 1931, the production of which at the Bolshevik plant was planned to resume in 1944. There is nothing strange in this decision, since the selected artillery system was distinguished by high lethality and, if installed on a tracked chassis, the Red Army would have at its disposal a high-power mobile destructive weapon. By order of the People's Commissar for Armaments DF Ustinov, in November 1943, a competition was announced for the creation of a new self-propelled gun, which received the semi-official designation "Vityaz".
A few weeks later, their preliminary designs for the new ACS were presented by factories # 100 NKTP, Uralmash Design Bureau and TsAKB. The first of them was a self-propelled gun carriage with a trailer, in which it was planned to place part of the gun ammunition. In some ways, this project resembled the French GPF 194, only the power of the ACS was higher.
The Uralmash design bureau presented two options for the competition at once: a 203-mm B-4 howitzer on the chassis of the KV-1S tank (modernization of the U-19 ACS) and a 203-mm howitzer or two 152-mm howitzers mounted on the chassis of two SU-122 ACS. Immediately before firing, it was proposed to connect the chassis, while preparation for firing took up to 40 minutes, versus 20 minutes for the project proposed by plant No. 100 NKTP.
At the same time, the works presented by factories No. 100 and Uralmash Design Bureau predictably did not find adequate support from the members of the commission, as they were distinguished by the increased technological complexity of the projects. As a result, only the TsAKB project under the C-51 index was approved. ACS S-51 was made on the basis of the KV-1S tank. It was soon established that the chassis of the tank had an insufficient length of the supporting surface and it needed to be improved. It was proposed to modify the chassis, expanding it to 7 or 8 road wheels. At the same time, the amount of improvements required to be carried out quite large, and the number of ACS produced would hardly have exceeded several dozen, so it was decided to abandon the idea of establishing the production of a new chassis. The final decision involved the installation of the artillery system on the unchanged chassis of the KV-1S tank, which was not the best option.
Design features
The S-51 self-propelled gun was an open-type self-propelled gun - a fully armored self-propelled gun body acted as a self-propelled gun carriage for the B-4 heavy howitzer openly mounted on top of it. The armored hull of the self-propelled guns was made of rolled armor plates with a thickness of 75, 60 and 30 mm, like the original hull of the KV tank. Reservations were differentiated and cannon-proof. Frontal armor plates had rational angles of inclination. In the bow of the hull there was a driver's seat, as well as ammunition and its carriers, the rest of the howitzer crew were outside the armored hull. The ACS transmission and engine were located in the stern. An emergency hatch was located in the bottom of the hull for an emergency escape from the vehicle.
The main armament of the S-51 ACS was supposed to be the modified 203, 4-mm B-4 howitzer. The howitzer was openly mounted on the roof of the armored hull and had vertical guidance angles in the range from 0 to 60 degrees, the horizontal guidance sector was 40 degrees (20 in each direction). The height of the line of fire was equal to 1070 meters when firing at a target with a height of 3 m. The range of a direct shot was 6, 9 km, the maximum firing range was 18, 26 km. A shot from a howitzer was carried out using a manual mechanical trigger. The B-4 gun was equipped with a piston bolt, and the howitzer's rate of fire was 1 shot in 1, 25-2, 5 minutes. In the firing position, the calculation of the gun was covered with a massive armor shield, which was removed during the march, and the howitzer barrel moved back to the stowed position.
Howitzer ammunition consisted of 12 rounds of separate cap-loading. The charges and shells were stored in the armored hull of the self-propelled guns, the possibility of their supply from the ground was also realized. The S-51 self-propelled guns could fire the entire range of ammunition from the B-4 howitzer, which included concrete-piercing and high-explosive shells weighing 100 kg. High-explosive shells F-623, F-625 and F-625D had an initial speed of 575 m / s, concrete-piercing G-620 and G-620T accelerated to 600-607 m / s.
ACS S-51 was equipped with a four-stroke V-shaped 12-cylinder V-2K diesel engine with a capacity of 600 hp. The engine was started using a ST-700 starter (power 15 hp) or using compressed air, which was placed in two 5-liter cylinders on the sides of the car. Fuel tanks with a total volume of 600-615 liters were located inside the armored hull of the vehicle in the engine compartment and the control compartment.
The ACS transmission was mechanical and included: a multi-plate main dry friction clutch “steel according to ferodo”; 2 multi-plate side clutches with steel-on-steel friction; 4-speed gearbox with range (8 forward and 2 reverse); 2 onboard planetary gearboxes. The unreliable operation of the S-51 ACS transmission was noted during its tests. This fact became another confirmation of the thesis that transmission defects remained one of the main shortcomings that were inherent in all KV tanks and armored vehicles based on it.
The chassis of the self-propelled gun repeated the chassis of the KV-1S tank. The ACS had an individual torsion bar suspension for each of the 6 gable road wheels (600 mm in diameter) on each side. Opposite each roller was a suspension balancer travel stop welded to the body. The sloths were in the front, and the drive wheels with removable pinion gear rims were in the back. The upper part of the track was supported by 3 small carrier rollers.
In general, the chassis, engine and hull of the serial KV-1S tank have not undergone any changes. The turret was dismantled from the tank, in its place a B-4 howitzer was installed on an open carriage. Since the weight of the S-51 ACS (weighing almost 50 tons) exceeded the weight of a serial tank with a fully equipped turret, the driving performance of the vehicle was rather mediocre.
The fate of the project
The first sample of the S-51 self-propelled guns began factory tests in February 1944, the tests were carried out according to an abbreviated program. At the same time, the interest in the project of self-propelled guns of high power was so great that, without waiting for their official completion, the self-propelled gun was transferred to ANIOP. It was here that all the major shortcomings of this machine surfaced to the full. Due to the high line of fire, the ACS swayed very strongly when fired and, by inertia, went back with a lateral shift. In the event that the angle of elevation of the gun was large enough, the recoil of the howitzer was so strong that the crew could not stay in their places. All this together led to a knockdown of the aiming and a large dispersion during firing (the installation of openers was necessary) and caused inconvenience to the crew of the ACS. In addition, the chassis of the KV-1S tank itself was poorly adapted to the installation of such a powerful weapon.
Comparing all the data obtained during the test, the GAU considered that the S-51 could still be sent to mass production, but this solution was not implemented in practice. First of all, this was due to the fact that the production of the KV-1S tanks was completed back in December 1942 - that is, it was possible to obtain the necessary chassis for the new ACS only by reworking the produced serial tanks. The second important problem was the absence of the B-4 howitzers themselves, the release of which was never deployed.
Also in the monograph by M. Kolomiets, which is dedicated to the KV tank, there is a mention of an ACS of a similar design, but armed with a 152.4 mm Br-2 cannon. This ACS was tested in July 1944 near Leningrad, and the question was even raised about starting its production on the basis of IS tanks in the fall of 1944. But this project was not implemented, and experiments with super-powerful self-propelled guns were continued after the end of the war. Then work was already underway on the creation of large-caliber artillery capable of firing shells with nuclear explosives. The serial self-propelled gun of this type has already become a fairly modern self-propelled gun 2S5 "Hyacinth".
