The Varshavyanka-class submarine HQ182 Hanoi, bought new from Russia, carried out its first operational tests in Vietnamese waters, Thanh Nien news agency reported.
The diesel-electric vessel -- Vietnam's first submarine -- was launched by the manufacturer Admiralty Shipyards in St. Petersburg, Russia, in 2012.
It underwent sea trials before being loaded onto a Dutch cargo ship for a journey of nearly 17,000 miles to Vietnam's Cam Ranh port.
Vietnam signed the $2 billion deal with Russia during a visit by Prime Minister Nguyen Tan Dung to Moscow in 2009.
All the subs -- called black holes because of their silent running when submerged -- are scheduled for delivery by the end of 2016, Thanh Nien reported. Two more subs are set for delivery later this year.
Vietnam intends to use the 3,100-ton vessels that can submerge to nearly 1,000 feet for inshore patrols.
The arrival of the submarine coincides with a declaration by China that requires foreign fishing vessels to seek Beijing's approval to operate in large swathes of the South China Sea.
But many of China's neighbors dispute China's unilaterally declared maritime boundaries as well as ownership of many of the island groups. They say China's declared boundaries infringe their legitimate 200-mile exclusive economic zones.
Vietnam, as well as the Philippines, condemned China's "wrongful acts," saying they aren't in the interests of peace and stability in the region, the Vietnam News Service reported.
Foreign Ministry spokesman Luong Thanh Nghi also condemned the first web and print newspaper published in China's Sansha City, set up officially in July 2012.
Sansha city is on Yongxing Island -- Woody Island -- part of the Paracel Islands group, what the Chinese call Xisha Islands.
Sansha is China's smallest prefecture-level city by both population and land area and has jurisdiction over more than 772,000 square miles of ocean that includes other disputed territories.
Ownership of the Paracel Islands has been a sensitive issue for the Vietnamese since losing administration of the group's Woody Island after a brief but deadly naval battle with the Chinese in January 1974.
Three of the four South Vietnamese navy warships retreated and the fourth was sunk by Chinese firepower, drowning dozens of soldiers and sailors including the ship's captain.
China gained control over the Paracel Islands and set up Sansha prefecture and city.
This year, for the first time in 40 years, Vietnam's state publications, including National newspapers such as Thanh Nien and Tuoi Tre, are marking the event, printing numerous articles on the battle, the BBC reported.
The Vietnamese government has been careful in the past not to whip up too much anti-Chinese feeling among the population for fear of street protests against Beijing's actions escalating into confrontations with police.
But that approach might be changing in the face of increasing Chinese statements of ownership of disputed territories and an increasing Chinese naval presence, including the launch of Beijing's first aircraft carrier, the Liaoning, in 2012.
The BBC quoted Ho Van Ky Thoai, a former rear admiral in the South Vietnamese navy and a commander during the 1974 battle, saying there has been "a shift in the Vietnamese government's approach to the subject" in the past several years.
"They have come to realize the clear danger of being swallowed by China. Unfortunately, it is years too late," said Ho, who lives in the United States.