This is coolbert:
From Strategy Page yet one more indicator, those nations whose territorial waters are adjacent to the South China Sea in an arms race with one another.
"Submarines: Vietnam Gets Game Against China"
"February 20, 2014: On the last day of 2013 Vietnam received its first submarine, a Russian made Kilo class boat. This is the first of six Kilos, which were ordered in 2009 and cost $2.1 billion. The Kilos are based at Cam Ranh Bay, a deep water port developed by the United States during the 1960s and has since then been a major shipping and ship maintenance facility."
"The Kilos weigh 2,300 tons (surface displacement), have six torpedo tubes, and a crew of 57. They are quiet and can travel about 700 kilometers under water at a quiet speed of about five kilometers an hour. Kilos carry 18 torpedoes or SS-N-27 anti-ship missiles (with a range of 300 kilometers and launched underwater from the torpedo tubes). The combination of quietness and cruise missiles makes Kilo very dangerous to surface ships."
. . . .
"The Kilos are the first subs the Vietnamese Navy has ever had are were obtained to provide some defense against growing Chinese naval power."
Growing Chinese naval power the environ of the Paracel Islands and the South China Sea.
Those Paracels and the contiguous sea bed adjacent to contested territory the two communist nations in contention.
That navy of Vietnam NOT having any experience with submarines I might well assume the learning curve to be long and arduous.
As described in the Tom Clancy novel "SSN" Vietnam and China in league with and opposed to American presence in the South China Sea.
Might have been true then  BUT NOT NOW!