ST. PETERSBURG, August 12 (RIA Novosti) – The third of six new “black hole” submarines that Russia is making for the Vietnamese navy will be floated out later this month, the shipbuilder said Monday, adding that the first of another six, for Russia’s own Black Sea Fleet, would be floated out in November.

The Varshavyanka-class (Project 636M) diesel-electric subs, dubbed by the US Navy as “black holes in the ocean” because they are nearly undetectable when submerged, are primarily designed for anti-shipping and anti-submarine missions in relatively shallow waters.

The first of the submarines, which completed its 100-day sea trials last month and for which a Vietnamese crew has been training since April, is expected to be delivered to that country in November, according to the manufacturer, Admiralty Shipyards.

Vietnam ordered the six submarines in 2009, counterbalancing China’s expanding maritime influence in the region. That contract, which also stipulated the training of Vietnamese crews in Russia, was reportedly worth $2 billion.

The Varshavyanka class is an improvement on the Kilo, with more advanced stealth technology and an extended combat range. Construction of the first Varshavyanka-class sub for the Black Sea Fleet, a vessel named the Novorossiisk, began in 2010 and has been completed ahead of schedule, the shipbuilder said.

The submarines, which feature 533-milimeter torpedo tubes and are armed with torpedoes, mines and Kalibr 3M54 (NATO SS-N-27 Sizzler) cruise missiles, displace 3,100 tons, reach speeds of 20 knots, can dive to 300 meters and carry crews of 52 people.