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ISU-152M Object 704 self-propelled gun

The Object 704 was a self-propelled gun based on the chassis of an IS-3 Heavy Tank. It was designed to carry the 152.4 mm ML-20SM model 1944. One prototype was developed of Object 704, which is housed today at the Kubinka Tank Museum in Russia. Developed in 1945 on the basis of the IS-2 and IS-3 vehicles, under the supervision of Joseph Kotin. One of the distinctive features was the balanced slope angle of armor plates. Passed trials successfully, but never entered service.

One prototype, developed in 1945, used elements of the IS-2 and IS-3 tanks. The overall height of the vehicle was reduced to 2240 mm, which was compensated with an increased width of the superstructure. The factory designation was Object 704. It was armed with the 152.4 mm ML-20SM model 1944 gun-howitzer, with a barrel length of over 4.5 meters (29.6 calibers) and no muzzle brake, which further increased the firepower of the gun.

It had a maximum range of 13,000 meters. The self-propelled gun carried 20 rounds of two piece (shell and charge) armor-piercing and high explosive ammunition. The armor-piercing round, weighing 48.78 kg, had a muzzle velocity of 655 m/s. The rate of fire was 1-2 round/min. The ISU-152 model 1945 had four hatches at the superstructure roof and one emergency hatch at the bottom of the hull behind the driver's seat, which had an armored cover.

The self-propelled gun carried two external fuel tanks (90 liters each) not connected to the supply system. The secondary armament of the fighting vehicle consisted of two 12.7 x 108 mm DShK machine guns, one anti-aircraft and one co-axial.

The protection was increased by placing thicker armor at more radical angles. In the area of the gun, where the mantlet combined with the hull front behind it and the housing of the recoil mechanism, the armor thickness was 320 mm. The ISU-152 model 1945 was the best protected of all experimental or production Soviet self-propelled guns of the Second World War. However, the radical incline of the superstructure walls combined with the increased recoil of the gun, due to the lack of a muzzle brake, significantly complicated the work of the crew, and for this reason mainly wasn't adopted.