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While the emerging Vietnam-US relationship is raising eyebrows in Beijing, growing ties between Moscow and its cold war beneficiary in Hanoi are also being closely watched.
Russia's expanding involvement with Vietnam has a direct impact on the South China Sea dispute, from Moscow selling six Kilo-class submarines to Hanoi to assistance to re-build naval facilities in Cam Ranh Bay off its south-central coast, regional diplomats believe.
A glittering prize in the cold war, Cam Ranh is seen as the best natural harbour in the region. Built by the US as an air and naval base to defend South Vietnam, Hanoi handed it over to Moscow in the late 1970s to house Russian submarines and its largest listening post in Asia.
Nearly a decade since the last Russians left, technicians are now preparing to help rebuild wharves and ship-repair facilities further north. Vietnam's Prime Minister Nguyen Tan Dung has said Cam Ranh will be opened to international navies at market rates.
Those efforts were highlighted last week when Nikolai Patrushev, the head of Russia's Security Council and former intelligence chief, visited Hanoi for talks. The Itar-Tass news agency reported that 'military and military-technical co-operation' would be discussed, along with expansion of the VietSovPetro oil production joint venture and possible joint efforts to build Vietnam's first nuclear power plant.
As well as Cam Ranh Bay, regional military attaches are closely eyeing updates on the submarine programme, particularly final delivery dates and the technology involved.
One Asian military attache close to developments said the Russians were planning to provide Vietnam with the best equipment for the Kilos, including latest generation sonar - which would give them an edge over China's own fleet of Kilos.