Dang Cong Ngu ruled a South China Sea archipelago for Vietnam for five years — but never once set foot in the place.

The now-retired 63-year-old governor of the disputed Paracel Islands was a king without a kingdom, railing from onshore exile against China’s capture of a strategic outpost central to the battle for Asia’s seas.

“We must fight to bring the territory back to the motherland,” a still-fiery Mr Dang declared in his old office, a poster proclaiming “The Paracels belong to Vietnam” in the background. “All Vietnamese, regardless of ethnicity, living inside or outside the country, know that’s the right thing to do.”

The elder statesman’s tough talk underscores why analysts see the islands and other China-Vietnam territorial disputes as potential flashpoints for confrontation that could pit Beijing against not just Hanoi but the new administration in Washington. Vietnam fought a border war with China as recently as 1979 — and, like other Southeast Asian countries, it is waiting nervously to see how Donald Trump’s government deals with Beijing and its territorial ambitions. China’s Xi Jinping is set to meet Mr Trump in the US next month.

Jonathan London, a Vietnam specialist at the Netherlands’ Leiden University, said: “For Hanoi and the Vietnamese, Beijing’s claims and its efforts to enforce these through aggressive practices remain clear and present threats to national security and sovereign interests. The great unknown in all of this is how the Trump administration will manage its relations with Hanoi — and in the region more broadly.”

Hanoi this week called for Beijing to stop running cruise ship trips to the Paracels, which are known as Hoang Sa in Vietnamese and the Xisha islands in Chinese. Those tours are part of a broader effort by Beijing to press its territorial claims to more than 90 per cent of the South China Sea, by building military facilities and artificial islands around the region.

The Paracels are a strategic way station south-east of China’s Hainan Island and its nuclear submarine fleet, in a wider seaway crucial to international trade. Beijing has built harbours, helipads and an air base in the archipelago, according to a report published last month by the Center for Strategic and International Studies’ Asia Maritime Transparency Initiative. China last year deployed anti-aircraft missiles in the Paracels and recently cleared still more land in preparation for possible further construction, according to satellite images, the latest of them released this week.

Communist-ruled Hanoi has made its own military preparations by strengthening ties with a range of international powers, including its former enemy the US. It has also increased security co-operation with Japan and India, which are both trying to curb Chinese expansion in the region.

Another element of Hanoi’s response is to maintain the bureaucratic fiction of its rule over the Paracels, which South Vietnamese forces lost to China in a 1974 battle while they were sliding to civil war defeat. The Paracel administration’s headquarters in the Vietnamese coastal town of Da Nang is filled with maps, photos and other historical documents ostensibly in support of its claim.

Le Dinh Re, a former South Vietnamese naval officer, recalled rescuing troops defeated by the Chinese in 1974. “I didn’t think China would still be there after 43 years,” said Mr Le, 73. “I really hope that one day I can set foot in Hoang Sa.”

The deployment of a Chinese oil rig in the area three years ago triggered anti-Beijing protests. Mobs later ransacked or torched hundreds of foreign-owned businesses in Vietnam’s industrial zones.

Nowadays Vietnamese fisherman at a Da Nang boat repair yard complain that they are chased away from the Paracels by Chinese vessels. Authorities say one large fishing boat was deliberately rammed: the plan is to put it in a new Da Nang museum devoted to the islands and Vietnam’s imagination of them.

“Our fishing boats are wooden and their vessels are steel, so we have no solution to this,” lamented Nguyen Vu, 35. “It’s our traditional fishing area, so we will never give it up.”

China has rejected both Vietnam’s Paracel sovereignty arguments and a wider ruling made by an international court in July against most of its South China Sea territorial claims. Beijing argues that the US is the aggressor in Asia because of its warship deployments and military bases around the region. China says it is committed to a long-planned code of conduct for countries in the region.

Hanoi is now sensitively placed as the Southeast Asian capital most publicly at odds with China’s maritime ambitions, after Philippine president Rodrigo Duterte sought to repair his country’s relationship with Beijing.

Vietnam’s belligerence is necessarily tempered by China’s far greater firepower — and by longstanding trade, cultural and political links between the two countries. But those caveats may yet be swept aside in this high-stakes and fast-evolving battle to rule the waves. Former governor Mr Dang says the Paracels’ administration-in-exile will push ever harder to build diplomatic and legal pressure on China to hand the islands over. “Ours is an extremely difficult and complex mission,” he said. “We must use all means that we can to regain Vietnamese sovereignty over Hoang Sa.”

By Michael Peel & Khac Giang Nguyen - The Financial Times - March 19, 2017