The Russian Navy's Kilo Class diesel-electric submarine Alrosa has suffered an engine malfunction during sea trials and has been towed to the port of Novorossiisk.
During a training exercise in the Black Sea the submarine experienced problems with its jet propulsion system.
A Russian Navy spokesman said the situation on the submarine was under control and there was no danger to the crew, according to RIA Novosti.
The submarine will continue the drills once the problem is fixed, the spokesman said.
The 73.8m-long and 6.6m-wide Kilo Class diesel-electric submarine has a submerged displacement capacity of 2,450t, can accommodate a crew of 53 and can cruise at a speed of 18kt.
The vessel's armament includes six 21in torpedo tubes and eight Strela-3 (SA-N-8 Gremlin) or 8 Igla (SA-N-10 Gimlet) missiles.
Based at a Russian naval base in Sevastopol on Ukraine's Crimean Peninsula, Alrosa is the only submarine in active service with the Black Sea Fleet.