The fifth of six Kilo-class submarines that Vietnam contracted to buy from Russia was launched at the Admiralty Shipyards in St. Petersburg on Sunday, Russian news agency Interfax reported.
The submarine codenamed HQ-186 Khanh Hoa is the fifth of the six Project 636.1 diesel-electric submarines ordered by Vietnam.
The first two subs, HQ-182 Hanoi and HQ-183 Ho Chi Minh City, arrived in Vietnam in early January and mid-March.
The third one, HQ-184 Hai Phong, was loaded into the Dutch-registered cargo ship Rolldock Star on December 16 and is scheduled to be delivered to Cam Ranh Port in late next month.
The fourth one, HQ-185 Da Nang, was launched on March 28 and is undergoing testing.
The sixth and last one, HQ-187 Ba Ria-Vung Tau, was built from May 28 and is scheduled to be delivered to Vietnam in 2016.
The six submarines, which are considered improvements over the older Kilo-class, feature six 533 mm tubes that can launch TEST-71 series anti-surface and anti-submarine heavyweight torpedoes.
They were built under a US$2-billion deal signed during a visit by Prime Minister Nguyen Tan Dung to Russia in 2009.
Under the contract, Russia will deliver all by 2016, train Vietnamese crews, and supply necessary spare parts.