MOSCOW, February 6 (RIA Novosti) – The Russian Navy ballistic-missile submarine Verkhoturye has returned to service with the Northern Fleet after completing a refit, Fleet Spokesman Captain First Rank Vadim Serga said on Wednesday.

The Project 667 class boat (NATO Delta 4) arrived at the main nuclear submarine base in Gadzhiyevo, Murmansk Region, after refit at the Zvezdochka shipyard at Severodvinsk, Serga said.

“During the refit, defense shipyard specialists made around a hundred improvements to the submarine,” Serga said.

The Verkhoturye is the second Northern Fleet Project 667 class boat to be refitted, he said.

“In August 2012, the Northern Fleet was reinforced with the Novomoskovsk submarine, which also underwent repairs and upgrade at the Severodvinsk defense shipyard,” he said.

Project 667 class boats displace 12,000 tons, have a maximum diving depth of 400 meters, a cruising speed of 24 knots and a crew of 140 men. They are armed with 16 Sineva intercontinental ballistic missiles.