There are reports that the nearly 30-year old, 3,500 ton, Bessmennyy ('Krivak-II') class ASW frigate Neukrotimyy ("Indomitable"), was struck by a mine a while rehearsing for end of World War II ceremonies. The ship was brought into a naval base and is apparently undergoing repairs. The mine may be a relic of one of the world wars, or perhaps a more recent Russian or even Swedish one that broke from its mooring line and drifted away. This sort of thing happens, but usually to merchant ships (which spend far more time at sea that warships.) Then again, the Neukrotimyy, flagship of the Baltic fleet,  may have had an internal explosion. That, because of the crowded design of Russian warships, and generally poor maintenance, is rather more common. The Russians merely reported that the ship was brought in for repairs, had holes in the hull and would have to be repaired. The navy refused to give details of what caused the damage, but the ship was seen with its stern low in the water.