On the afternoon of 28 October 1955, Novorossiysk returned to Sevastopol from a gunnery drill in the Black Sea. The battleship anchored at Sevastopol’s #3 mooring buoy, adjacent to the Soviet Naval Hospital, about 1,000′ off the beach. The water at the mooring buoy is about 60′ deep. There were 1,542 sailors aboard; far more than the intended WWII complement but not uncommon for a warship being used for training.
The captain of Novorossiysk departed ashore, leaving the executive officer in command. After the evening meal, about 240 of Novorossiysk‘s core crew departed for shore leave. At the same time, 200 cadets came aboard for the next planned drills, along with several dozen (the total is disputed) naval infantry soldiers and shipyard mechanics. In all, there were about 1,530 people aboard Novorossiysk.
At 01:31 on 29 October 1955, a massive explosion occurred directly underneath the starboard bow.
At 01:30 hrs there was an explosion, making a 4-by-14-meter (13 by 46 ft) hole in the forecastle forward of 'A' turret. The flooding could not be controlled and she later capsized.
A total of 609 Soviet sailors died. A hundred men died immediately from the blast. Four hundred and forty-six men from the ship died during the capsizing. Fifty-eight damage controlmen from nearby ships and five men from an ashore specialist salvage team at Sevastopol base also died during the capsizing. Another forty-eight sailors were seriously injured during the capsizing. It was the worst peacetime catastrophe in the Soviet navy’s history.
The cause of the explosion is still unclear. The officially named cause, regarded as the most probable, was a magnetic RMH or LMB bottom mine, laid by the Germans during World War II and triggered by the dragging of the battleship's anchor chain before mooring for the last time.
Subsequent searches located 32 mines of these types, some of them within 50 meters (160 ft) of the explosion. The damage was consistent with an explosion of 1,000–1,200 kilograms (2,200–2,600 lb) of TNT and more than one mine may have detonated.
Novorossiysk was stricken from the naval register on 24 February 1956, salvaged on 4 May 1957, and subsequently scrapped.