Deepest operational combat submarine

A Russian K-278 submarine reached a depth of c. 1,027 m (3,350 ft) on 4 August 1985 in the Norwegian Sea. The first (and only) K-278 keel was laid down at Severodvinsk in Arkhangelsk Oblast, Russia, on 22 April 1978, launched on 3 June 1983 and commissioned on 28 December 1983. A prototype nuclear-powered attack sub, it featured a double hull – including an inner hull of titanium – that allowed for deeper operations than any other combat submarine. The most widely reported depth is 3,345 ft, although a maximum of 1,027 m was determined from the Deepstorm website. The sub was built with a maximum operational depth of 1,005 m (3,300 ft) and a never-exceed-depth of 1,250 m (4,100 ft). It sank, following a fire, in 1989 and now lies at on the bed of the Barents Sea.