Due to short circuits that took place in III and VII compartments simultaneously at a depth of 120 metres (390 ft), a fire spread through the air-conditioning system.

Fifty-two crewmen, including the commander, Captain 2nd Rank Vsevolod Bessonov, re-boarded the surfaced submarine that was to be towed.

This was the first loss of a Soviet nuclear-powered submarine, which sank in rough seas as it was being towed in the Bay of Biscay of the North Atlantic Ocean.

All hands on board died due to carbon monoxide poisoning and the flooding of the surfaced submarine during 80 hours of damage control in stormy conditions.

K-8 sank with four nuclear torpedoes out of total 24 on board to a depth of 4,680 metres (15,350 ft) approximately 490 kilometres (260 nmi) northwest of Spain.