Designed and built on the chassis of the KV-1S. The development of a prototype started in January 1944. The 203-mm B-4 howitzer was mounted on the restored hull of a KV-1S. From March 1944 through to the beginning of April, the vehicle underwent trials. Despite successful trials, the S-51 never entered mass production.
The technical characteristics shown are for the Siege mode
Characteristics are specified for a vehicle with crew members trained to 100%.