This heavy SPG on the basis of the ISU-122S was developed in 1944, with a prototype built in October. The 130-mm S-26 gun, based on the B-13 naval gun, was mounted on the ISU-122S. The vehicle underwent automotive and firing trials by 1945, but penetration characteristics were inferior to those of the 122-mm guns, and the war was drawing to a close, so the vehicle never entered service.
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Time for the successive autoreloading of each shell into the magazine.
The improved system allows the time to be decreased for autoreloading the next shell upon firing the loaded shell when the corresponding indicator is displayed
Characteristics are specified for Siege mode.
The technical characteristics are displayed for the charged turbine mode.
Characteristics are specified for Rapid mode.
Reload time of the first and second guns on double-barreled vehicles.
Characteristics are specified for vehicles with crews trained to 100%.