In 1943, after the Soviet Red Army installed the ISU-152 heavy self-propelled artillery, the design team undertook the new task of developing a
self-propelled artillery equipped with A-19 122mm and howitzers. At the end of 1943, the Design Bureau of the No. 100 Experimental Factory
began to develop and produced a prototype in December, numbered ISU-122. It is very close to the ISU-152. The difference is that the main
gun is changed from the ISU-152 ML-20S 152mm howitzer to the A-19S 122mm howitzer. Not only the chassis is the same, but the gun mount
is the same.
In March 1944, the Soviet Red Army decided to equip the ISU-122 self-propelled artillery. In April, mass production of this self-propelled ar‐
tillery began at the Kirov plant in Chelyabinsk. The armored car body is welded by rolled armored steel plates. The thickest part of the front ar‐
mor is 90mm, the sides are 75mm, the rear is 60mm, and the top of the battle room is 30mm thick. The A-19S gun has a very small improvement compared with the A-19. After analyzing the results of the Kursk battle, the Soviet Union found that the A-19 could destroy the “Tiger” heavy tank, so it was listed as a key model and installed on tanks and self-propelled artillery. ISU-122 is the first self-propelled artillery equipped with an improved A-19, with a muzzle velocity of 800 m/s, a direct firing distance of 2.5 kilometers, a max‐imum range of 14.3 kilometers, and 30 rounds of ammunition. In October 1944, the air defense DShK 12.7mm machine gun was installed on
the ISU-122.
ISU-122 has a combat weight of 46 tons and 5 crew members: the commander, the driver, the gunner, and two loader. Equipped with a 520-
horsepower V-2-IS diesel engine with a maximum speed of 35 km/h and a maximum stroke of 220 km.
The Soviet army used the ISU-122 heavy self-propelled artillery as an assault gun and tank destroyer to provide direct or indirect fire support
for the infantry and destroy the enemy’s heavy tanks for the armored forces. The 25-kilogram BR-471 armor-piercing shell that A-19S and how‐
itzer can fire can destroy almost any German tank. HE-471 high-explosive grenade is usually used against armored vehicles. The huge impact
and explosion are enough to make the enemy’s armored target lose combat effectiveness, even if the armor is not penetrated, it can still cause
fatal damage.
In order to increase the rate of fire of the A-19, the screw-breaking breech block was replaced with a semi-automatic wedge-type breech block, which was shaped as D-25. The D-25T was installed on the IS-2 heavy tank, and the D-25S was installed on the late ISU-122 self-propelled gun.
This later type is called ISU-122S (pictured). The gun shield is quite different from the ISU-122 and is equipped with a muzzle brake.
ISU-122 self-propelled artillery played an important role in the final stage of the Second World War. From April 1944 to August 1945, a total of 1,735 ISU-122s were produced. After the war, the Soviet Union modernized the ISU-122 and remained in service until the mid-1960s. After the founding of New China, a small amount of ISU-122 self-propelled artillery was imported, which became one of the earliest heavy equipment of the People’s Army.