Vietnam's main naval bases (above). The Navy consists mainly of Russian built smaller craft. The (potentially Klub missile armed) Gepard class frigates and Klub armed Improved Kilo submarines are the most powerful units. The TT-400TPs gunboats are locally built. The Navy is orientated toward low-end Chinese actions (Chinese coast guard, naval militia/trawler, contentious oil rigs and verbal threats) in the South China Sea and periodic clashes with China.
Russia's delivery of five Improved Kilo submarines to Vietnam over the last few years has been very efficient. In early February 2016 the fiftth Kilo HQ-186 Da Nang was delivered to Vietnam's major naval base at Cam Ranh Bay. The sixth, final, submarine, HQ-187 Vung Tau, is expected to be delivered later in 2016.
Vietnam maintains relations with several regional powers to counterbalance China's power.
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Unlike other Southeast Asian/ASEAN countries Vietnam has defended itself from large outside powers and beaten them in the last 50 years. This has contributed to a rational defence posture that has not been tainted by the regional norm of inefficiency.
The methodical, focussed nature of Vietnam's defence force is only equaled in Southeast Asia by Singapore. Singapore recognises it is dwarfed by its Indonesian and Malaysian neighbours so Singapore has bought high tech weapons from the US and Western Europe. In return Singapore has tangible support from the US military.
Vietnam's purchase of six Russian submarines is just part of Vietnam's commercial and strategic relationship with Russia. Here were tentative early days of the submarine deal. This relationship is not an alliance but Vietnam realises that when it again is threatened by China (as in 1979-1990) Russia and to some extent the US can exert political and economic pressure on China.
On land Vietnam can inflict high casualties on encroaching Chinese forces - as Vietnam did in the 1979 Border "Sino-Vietnamese" War. That 1979 Border War was large, with more than 100,000 Chinese troops and militia killed. But Vietnam realises it cannot beat China alone.
Vietnam's submarines can do major damage to China through putting China's sea trade (especially oil and LNG supplies) at risk. Vietnam's submarines are armed with Klub missiles that have a land attack capability. Chinese leaders and military would lose considerable face if Vietnamese missiles hit such major Chinese cities as Guangzhou and Shanghai. Vietnam's frigates and corvettes could also be potentially fitted with Russia's newly proven Klub/Kalibr land attack missiles.
In addition to Russia and the US Vietnam has close relations with such regional powers as India, Japan, South Korea and Australia.
Although there is the strategic threat from China Vietnam has close economic relations with China.
Australia also has the conundrum of close economic relations but frosty strategic relations with China.
Vietnam also has long term nuclear energy aspirations - a complication not lost on China. Here is an earlier nuclear report on Submarine Matters.
Pete