Date of Incident: 15 December 1952
Returned to Service: No
The diesel-electric submarine S-117 was lost on or about 15 December 1952 due to unknown causes in the Sea of Japan.
S-117 left Vladivostok on 14 December to particpate in a battle exercise. Late that evening she reported problems with her starboard diesel engine. A short time later she acknowleged a message sent about a floating mine that had been spotted in the area. Early the next morning, S-117 reported that repairs to the starboard engine had been successfully completed. However, she missed the next scheduled communication period, at 1700 hours on 15 December.
Extensive searches were carried out, both in the days immediately after S-117 disappeared and the following year, once the weather improved. No trace of the submarine has been reported.
Possible causes for the loss of S-117 are an operational accident, such as a battery explosion, flooding, or other similar accident, collision with a surface ship, collision with the report mine (or an unreported mine), or collision with an American submarine.
The most likely cause was collision with a surface ship. Russian authorities discovered that a Russian civilian government ship passed through the same area, at the same time, as S-117, and that she had halted for no apparent reason in this area. The officers and crew reportedly gave confusing reasons for the vessel stopping in the area. Furthermore, damage was discovered to the hull of the vessel. However, since S-117 was never found, it was not possible to confirm this theory.
The next most likely cause was some kind of operational accident.
(Russian language submarine site http://submarine.id.ru; page http://submarine.id.ru/memory/S117.htm)
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