The Great Patriotic War, as well as the Second World War in general, is often called the war of engines. Indeed, the appearance in the troops of a huge number of motorized equipment radically changed the tactics and strategy of the war. One of the classes of new technology was the tank. The appearance of more powerful engines allowed the tank designers to launch a real arms race: already in the middle of World War II, no one had any doubts that the cornerstone of the practical application of the tank was the confrontation between the gun and the armor. So the thickness of the armor plates and the caliber of the guns were increased.
Perhaps the most effective self-propelled domestic means of fighting enemy tanks was the ISU-152 self-propelled gun. The 152-mm ML-20S gun made it possible to reliably hit enemy armored vehicles at such ranges from which the Tigers or Panthers simply could not respond. In the army, this self-propelled gun was even nicknamed "St. John's Wort" for the effective destruction of German "cats". Well, stories about how a German tank tore off a tower after being hit will excite the imagination of people for a long time and cause a lot of controversy. At the same time, the ML-20S gun was essentially a howitzer cannon and, as a result, had a medium-length barrel and a relatively low muzzle velocity. The increase in the length of the barrel could significantly increase the combat performance of the self-propelled gun. For this reason, at the very beginning of 1944, the design bureau of plant No. 100 under the leadership of J. Ya. Kotina is taking the initiative to create an updated version of the ISU-152. As a new six-inch gun, OKB-172 (chief designer I. I. Ivanov) proposed its new development - the BL-8 cannon. This gun was created on the basis of the pre-war BL-7 and was originally designed taking into account the features of the installation on self-propelled guns. Kotin was satisfied with the proposal and the ISU-152-1 project (the designation consists of the caliber and number of the experimental modernization of the original ACS) began to be created specifically for this gun.
The Great Patriotic War, among other things, was remembered for the emergency pace of work. ISU-152-1 also suffered such a “fate”. The first prototype of this self-propelled gun mount was sent to the test site in July. Outwardly, the new car turned out to be formidable. A long barrel with a huge muzzle brake was added to the harsh appearance of the original ISU-152. Most of the design was transferred to the experienced self-propelled gun practically unchanged. Therefore, the armored hull, as well as on the original ISU-152, was divided into two compartments - engine-transmission and combat. The power plant still consisted of a V-2-IS 12-cylinder V-shaped diesel engine (520 hp), a multi-plate main clutch and a four-speed gearbox. The chassis was also completely borrowed from the ISU-152.
The main, and in principle, the only difference between the ISU-152-1 and the ISU-152 lay in the new weapon. The BL-8 cannon was mounted in a frame on the frontal armor plate. The attachment point allowed aiming the gun in the range from -3 ° 10 'to + 17 ° 45' vertically and from 2 ° (left) to 6 ° 30 '(right) horizontally. The difference in the horizontal guidance angles is explained by the peculiarities of the installation of the gun: it was not mounted in the center of the frontal plate, which became the reason for the restrictions due to the movement of the breech in the wheelhouse. The 152-mm BL-8 cannon had a piston bolt and a barrel blowing device after firing. We should also dwell on the muzzle brake of the gun. As you can see from its design, it works in an interesting way. When fired, the powder gases hit the front glass and create a forward impulse. After the impact, the gases under pressure follow back, where some of them are thrown out through the side windows, and the remaining flow is redirected to the sides by the rear brake disc. Thus, it was possible to significantly reduce the amount of powder gases going towards the ACS cabin without any significant loss in brake efficiency. The gun ammunition consisted of 21 rounds of separate loading of various types. Shells and casings were placed in the same way as on the original ISU-152, along the sides and at the rear wall of the wheelhouse. The ammunition nomenclature has not changed either. These were armor-piercing tracer shells 53-BR-540 and high-explosive fragmentation 53-OF-540. For self-defense of the crew, it was supposed to equip the self-propelled gun with two PPSh or PPS submachine guns with ammunition and a set of grenades. Also, in the future, it was planned to install a large-caliber machine gun DShK on the tower. However, the ISU-152-1 never received additional weapons.
The ISU-152 crew of five - the commander, driver, gunner, loader and lock - also survived on the ISU-152-1.
In July 1944, a prototype of the ISU-152-1 under the name "Object 246" was delivered to the Rzhevsky test site. Already the first shooting and trips around the range left an ambiguous impression. The longer barrel of the gun significantly increased the muzzle velocity of the projectile. So, the armor-piercing 53-BR-540 had an initial speed of 850 m / s versus 600 m / s for the ML-20S howitzer cannon. As a result, the shelling of armor plates of various thicknesses made a splash among the testers. From a kilometer range, the experienced self-propelled gun was guaranteed to penetrate the armor of any German tanks, even if it hit at small angles. As an experiment, the thickness of the armored plate on which the fire was fired was gradually increased. 150 millimeters - pierced. 180 - pierced. Finally, 203. Even such armor could be penetrated along the normal.
BL-8 based on ISU-152 (photo
On the other hand, the updated self-propelled gun had enough problems. The muzzle brake of the new design did not show the design characteristics, and the barrel turned out to be less tenacious than required. In addition, its length made it difficult to move normally over rough terrain. The five-meter "pipe", coupled with small vertical guidance angles and the absence of a rotating tower, very often literally rested on the ground and needed help from the side. Finally, the new gun was heavier than the ML-20S and increased the load on the front of the suspension. Deteriorated maneuverability and cross-country ability.
The experience with the ISU-152-1 was recognized as partially successful, but requiring serious improvements. Ideally, to bring the new self-propelled gun into a normal form, a new engine of greater power was required, a new design of the suspension of the gun with large vertical guidance angles, which ultimately would require re-arranging the entire armored chamber and even changing its dimensions. The gain in combat characteristics was considered insufficient reason for such a serious revision. However, the only experienced self-propelled gun ISU-152-1 did not disappear and became the basis for the next modernization.
As a last chance to upgrade the ISU-152, the designers of plant No. 100 and OKB-172 were allowed to modify the gun and test the self-propelled gun equipped with it. By the end of the 44th year, the design team of I. I. Ivanov reduced the length of the barrel of the BL-8 cannon, modified the breech and the design of the mountings to the frontal armor plate of the self-propelled carrier. The resulting BL-10 gun was installed on the "object 246" instead of the BL-8, which was recognized as unsuccessful. The second version of the modernization of the ISU-152 was named ISU-152-2 or "object 247". The tests of "object 247" that began in December 1944, oddly enough, showed no improvement in the situation in any area. The maneuverability and maneuverability remained the same as that of the ISU-152-1, and the armor penetration indicators, in turn, dropped slightly.
ISU-152 with BL-10
By the time the ISU-152-2 tests were completed, it became clear that such modernizations of the Hypericum were no longer of practical value. Self-propelled guns with ML-20S cannons were already enough, and the combat characteristics allowed them to completely calmly carry out their tasks until the end of the war. And the post-war prospects of such a machine were seen as very vague. The Cold War was not even in the air yet, and the main problem of Soviet industry was bringing the Great Patriotic War to a victorious end. Bringing the BL-10 cannon was considered unnecessary and stopped, and the only built copy of the ISU-152-2, previously the former ISU-152-1, was sent for storage. Today it can be seen in the Armored Museum in Kubinka.
