A Soviet submarine wreck from World War II has been discovered in the Baltic Sea, the Swedish military said Monday. It is believed the sub disappeared in 1941.

The Soviet submarine had been lying on the floor of the Baltic for 71 years before the Swedes found it  off the coast of Oland, a Swedish island, reports Reuters.

The Swedish Defense Forces believe the submarine wreck is the S-6, which went missing in September 1941, three months after Hitler's invasion of the Soviet Union. Although it is unclear how it sank, the Swedish military believes that the Soviet sub ran into a German mine, notes Reuters. The waters surrounding Oland were mined by the Germans during World War II. According to Agence France Presse, the area where the submarine wreck was discovered was known as the “Wartburg minefield.” 

In a statement, the Swedish Defense Forces said, “In the autumn of 1941 several Russian submarines left their home bases to patrol the Baltic Sea. Several of them never returned. One of them has now been found, blown up into large pieces, southeast of Oland,” notes AFP.

The wreck was first discovered by a group of Swedish divers and later confirmed by the military following a survey of the wreck by HMS Belos, a submarine rescue ship. The Soviet sub had broken into two pieces, the bow and stern. The bow was discovered about 65 feet north of the stern.

Swedish officials notified Russia of the submarine wreck discovery to allow the government to notify the crew's families and conduct a memorial ceremony, notes Reuters.

The S-6 was not the first Soviet submarine found by the Swedish Defense Forces. In 2009, a Soviet submarine, S-2, was found in waters between Sweden and Finland, notes AFP. The S-2, much like the S-6, was sunk by mines in January 1940 and had at least 50 crewmen on board at the time it sunk, reports AFP. The video of the submarine wreck was taken by the HMS Belos.