Soviet submarine S-363 was a Soviet Navy Whiskey-class submarine of the Baltic Fleet. It ran aground on 27 October 1981 on the south coast of Sweden, approximately 10 km (6.2 mi) from Karlskrona, one of the largest Swedish naval bases.

The captain initially claimed that simultaneous failures of navigational equipment had caused the boat to get lost although the boat had already somehow navigated through a treacherous series of rocks, straits, and islands to get so close to the naval base.[3]

he Soviet captain, after a guarantee of his immunity, was taken off the boat and interrogated in the presence of Soviet representatives.[4]

Although the presence of nuclear weapons on board S-363 was never officially confirmed by the Soviet authorities,[5] the vessel's political officer, Vasily Besedin, later confirmed that there were nuclear warheads on some of the torpedoes and that the crew had been ordered to destroy the boat, including the warheads, if Swedish forces tried to take control of the vessel.[6]

The submarine was stuck on the rock for nearly ten days. On 5 November, it was hauled off the rocks by Swedish tugs and escorted to international waters, where it was handed over to the Soviet fleet.[4]