In the beginnings after WWII the NATO countries only maintained very weak naval forces in the area of the Baltic Sea. The Soviet Navy assumed that they could quickly force their way from their traditional base in the Baltic Sea to the ocean. Not until 1956, after the rearmament of Germany, the NATO forces, especially the German and Danish Navy strengthened their position in the Baltic Sea to be able to defend the exits to the ocean. Having done that meant for the Soviet Navy that they would no longer be able to easily interfere any traffic of NATO enforcements in the North Atlantic anymore. Hence the basis in the Barents Sea were enlarged, among them Murmansk. Those bases enabled the Soviet Navy to advance to the North Atlantic Ocean if necessary.Also in the late 50s of the last century, the Soviet Navy started to build up their fleet of nuclear-powered submarines. Those vessels, mainly built in Sewerodwinsk, were also stationed with the Red Banner Northern Military Fleet (Northern Fleet) to secure their free access to the open sea. In that time, the Northern Fleet became the most powerful among the four soviet fleets.