In the former Soviet Union/Russia, 247 nuclear submarines and five nuclear-powered surface ships were built in the period from 1955 to 1996. In addition, a nuclear reactor which can be installed in diesel powered submarines was also built. Nuclear powered naval vessels are in service with the Northern Fleet (2/3) and with the Pacific Fleet (1/3), but have never been assigned to either of the other two Russian Fleets (the Black Sea Fleet and the Baltic Fleet.) Until the end of the 1980s, the Soviet Navy had more nuclear submarines than all other countries put together. As a result both of the START II disarmament treaty and the high age of some of the earlier generations of Soviet submarines, 138 Russian submarines are now no longer operative. This number is expected to increase over the years to come as more of the ageing classes of submarines are decommissioned and dismantled. At the present time, there are 67 nuclear submarines and two nuclear-powered battle cruisers in service with the Northern Fleet, while in the Pacific Fleet, there are 42 operative nuclear submarines, one nuclear powered battle cruiser, and one nuclear powered communications ship.