Vietnam in 2009 ordered six of the Russian-made submarines -- dubbed “black holes in the ocean” by the US Navy because they are nearly undetectable when submerged -- in a step seen as an effort to counterbalance China’s expanding maritime influence in the region.

According to the defense industry source, the first craft in the order is to be loaded on a stevedore barge on November 11 and towed to Vietnam, where it will be officially transferred to the country’s navy.

“The second vessel will be delivered in the beginning of next year, possibly in January, while the third will be also transferred in 2014,” the source said.

The contract, which also includes provision for the training of Vietnamese submarine crews in Russia, is reportedly worth $2 billion.

The submarines are being built at St. Petersburg’s Admiralty Shipyards. All six boats are due for delivery by 2016.

The source also said Thursday that three Varshavyanka-class submarines will be delivered by Admiralty Shipyards to Russia’s Black Sea Fleet next year.

Work on building the first sub, the Novorossiisk, began in August 2010, followed by Rostov-on-Don in November 2011 and Stary Oskol in August 2012.

The Project 636 class boats displace 3,100 tons, reach speeds of 20 knots, can dive to 300 meters and carry crews of 52 people.