Perhaps the most effective means of self-propelled anti-Russian enemy tanks was ISU-152 self-propelled guns. 152-mm gun ML-20S allowed firmly strike the enemy armored vehicles at such distances from which the "Tigers" or "Panther" simply could not answer. The troops of this self-propelled even dubbed the "St. John's Wort" for the effective settlement of the German "cats". But the stories about how German tanks frustrated after hitting the tower, it is long more will excite the imagination of the people and cause a lot of controversy. At the same time, tool ML-20S was the essence of his own gun-howitzer and, as a result, had a trunk of medium length and a relatively small initial velocity of the projectile. Increasing the length of the barrel could significantly increment fighting characteristics of self-propelled guns. For this reason, at the beginning of 1944 the plant design office number 100 under the control of ZY Kotin in the active order is starting a refreshed version of the ISU-152. As a new six-inch guns OKB-172 (chief designer Ivan Ivanov) offered its latest development — the gun BL-8. This tool was created on the basis of pre-war BL-7 and initially projected, taking into account the features installed on self-propelled guns. Kotin suit and a draft proposal ISU-152-1 (designation consists of caliber and most experienced room upgrade primary ACS) was created specifically for this gun.
Lofty Russian, among other things, remember the pace of work and rush job. ISU-152-1 is also understood this "fate." The first prototype of this self-propelled artillery systems were sent to the landfill in July-month. Outside brand new car came out harsh. By the terrible face of the initial ICS-152 added a very long barrel of the gun with a large muzzle brake. Most of the designs ran across the most experienced virtually no self-propelled configurations. Because hulls, as in the original ISU-152, was divided into two departments — power pack and combat. The power plant as previously consisted of a 12-cylinder V-type diesel-2-IC (520 hp), a multi-plate clutch and head chetyrehstupnoy box. Chassis, too, was absolutely taken from the ISU-152.
The main thing, yes, in principle, and the only difference between the ISU-152-1 of the ISU-152 wings in a brand new cannon. Gun BC-8 was placed in a frame on the front armor plate. Fastening element helps to build a gun in the range from -3 ° 10 'to +17 ° 45' vertical and 2 ° (to the left) to 6 ° 30 '(on the right) horizontally. The difference in the angles of traverse clarifies the installation tool: it was mounted off-center-plate, which was a prerequisite constraints due to the movement of the breech in the wheelhouse. 152-mm gun BC-8 had a piston valve and purge the device barrel after the shot. Separately worth the brakes on the gun muzzle brake. As its structure, it operates an exciting circuit. When fired, the powder gases beating in the front glass and make impulse moves forward. After impact, the gas pressure is followed by reversal, where part of them is ejected through the side windows, and the remaining stream is routed to the back plate of the brake. So Makarov could substantially reduce the amount of propellant gases in the exhaust side of the ACS logging without any special losses in the effectiveness of the brakes. Gun ammunition consisted of 21 rounds of separate loading of different types. The shells and liners fit as well as on the initial ISU-152, on the sides and the back wall cutting. The range of ammunition and did not undergo configurations. It was the armor-piercing tracer rounds 53-BR-540 and high-explosive 53-RP-540. For self-defense self-propelled gun crew was supposed to equip with 2 pistols, machine guns PCA or PPP dial with ammunition and grenades. Also planned in the future to install the tower mnogokaliberny DShK. But additional weapons ISU-152-1 ultimately never received.
ISU-152 crew of 5 members — commander, driver, gunner, loader and the castle — and also remained on the ISU-152-1.
In July 1944, a prototype of the ISU-152-1 under the title "object 246" was delivered to the landfill é. Already the first shooting and a trip to the landfill left-valued memory. Over very long gun barrel significantly increased the initial velocity of the projectile. So, armor-piercing 53-BR-540 had an initial speed of 850 m / s vs. 600 m / s in the gun-howitzer ML-20S. As a result, firing armor plates of different thicknesses made a real splash in the middle of the Test. With the most experienced kilometer-range self-propelled guaranteed pierced the armor of all German tanks, while even in the case of exposure to the small angles. In order to experience the thickness of armor plate, which was carried out by fire, uniformly increased. 150 mm — punched. 180 — punctured. Finally, 203. The normal way even such armor.
On the other hand, self-propelled refreshed enough problems. Muzzle Brake newest design did not show the calculated features, and trunk was the least resilient than was required. In addition, it interferes with the normal length of a cross-country move. Five-meter "tube" along with small angles and the lack of vertical lay swivel head very often almost rested against the ground and needed help from the outside. In the end, the new gun was heavier than ML-20S and increased load on the front of the chassis. Exacerbated maneuverability and permeability.
Experience with the ISU-152-1 is recognized partly successful, but require severe modifications. In the benchmark, to bring the latest self-propelled guns in the usual form required new engine more power, brand new suspension design tools with vertical lay bolshennymi corners that ultimately would require a rebuild all bronerubku and even change its size. Winning the battle properties considered cause for missing so severe revision. But only the most experienced SPG ISU-152-1 has not disappeared and became the basis for the next upgrade.
As a last chance to update the ISU-152 designers plant number 100 and OKB-172 was allowed to refine and test the gun fitted to her self-propelled. By the end of the 44-year design team II Ivanov has reduced the length of the barrel of a gun BL-8, modified the design of the breech and attachment to the frontal armor plate self-propelled vehicle. The resulting instrument BL-10 was set to "object 246" instead of the recognized poor BL-8. Second upgrade option ISU-152 was named the ISU-152-2 or "object 247." Begun in December 1944,
tests of the "object 247", surprisingly, showed no improvement in any area. Maneuverability and flotation are the same as that of the ISU-152-1, and armor penetration characteristics, in turn, fell a little.
By the end of the test ISU-152-2, it became clear that such modernization of the "St. John's Wort" has no practical value. Self-propelled guns with the ML-20S and it was pretty, well, fighting properties allow them to do their very relaxed tasks right up to the end of the war. Well, the post-war prospects similar machines seen very vague. Cool war has not even been in the air, but the main problem of Russian industry was bringing majestically Russian war to the bitter end. Bringing the gun BL-10 was considered unnecessary and finished, and built the only instance of ISU-152-2, earlier last ISU-152-1 was sent to storage. Now it is possible to see in armored Museum in Kubinka.