08 April 1970,
A nuclear submarine suffered an accident in the Gulf of Bizkaia. K8 was a Soviet submarine carrying two atomic reactors and several nuclear warheads. After the military manoeuvres, two fires were triggered inside, causing a chain of accidents. Although most of the crew were taken out, four days later, on 12 April it sank with 52 crews and nuclear cargo at 4,680 metres deep.
Source:
Unai Aranzadi, a nuclear submarine at the bottom of the Gulf of Bizkaia (Naiz, 6 April 2019).