Vietnam's Communist regime has hoped that deferential behavior might temper its giant northern neighbor's South China Sea ambitions. But by sending the deep sea drill ship Haiyang 981 to explore for oil just off Vietnam's central coast, Beijing has dashed that hope and posed a terrible dilemma for Hanoi.

The Vietnamese were the fiercest critics of China's expansive claim to sovereignty over the South China Sea (SCS) in 2009-2011, when Hanoi hoped to rally an Association of Southeast Asian Nations united front backed, at least implicitly, by US naval might. ASEAN's collective disinclination to challenge China left the US with no foundation for a robust policy in the South China Sea. Nor did Washington ever seem keen to offer defensive assurances to the non-Chinese claimants, not even to treaty allies in Manila.

Under those circumstances, conciliation, however unpopular with public opinion, seemed more likely to sooth Beijing and induce restraint. Particularly since the Xi Jinping government was installed in November 2012, Vietnam's leaders have made a determined effort to patch up relations with their hulking neighbor.

While China enforced its claim to reefs within Philippine waters in 2012 and 2013, Hanoi's response was distinctly muted. When China sent a flotilla to plant a flag on the James Bank just off East Malaysia, Hanoi seemed unperturbed. When Chinese coast guard vessels swept Vietnamese fishermen from traditional fisheries near the disputed Paracel Islands, the fisheries hotline to Beijing did not hum with protest. When tensions flared between Japan and China over the Senkaku/Diaoyu Islands, Hanoi stayed studiously clear of even verbal involvement. When Manila asked Hanoi to join in suing China in the International Court of Justice, the Vietnamese government ducked.

Over the past two years, only two events -- both in June 2012 -- have provoked Hanoi to public wrath. The first was an egregious invitation to foreign oil companies by the Chinese National Offshore Oil Company (CNOOC) to bid for permission to explore blocks just off the Central Vietnam coast. The second was Beijing's establishment of "Sansha City" on a Paracels islet as the administrative and military center for Beijing's growing SCS presence.

When circumstances have permitted over these past two years, Vietnamese leaders have missed no opportunity to laud fraternal relationships with Chinese counterparts. Hanoi appears to have reasoned that relative detente was possible once Xi and his fellows had a good grip on the levers of power.

During the run-up to the generational succession in Beijing, Middle Kingdom chauvinists were strident in their anti-Vietnamese agitation. Hanoi doubtless hoped that as power settled at the center, Xi and his colleagues would instruct subordinates to throttle back anti-Vietnamese propaganda and eschew provocative actions. In earnest of its hopes for detente, Vietnamese internal security agencies stepped up pressure on dissident bloggers, a gesture to Beijing that did not succeed in stifling criticism of the regime's allegedly “soft” policy vis-a-vis China.

At the Shangri La Conference last September, Prime Minister Dung urged China and other participants to cooperate in "building strategic trust." Dung's eloquence was was warmly applauded but, now that the Haiyang Shiyou 981 has dropped anchor 120 kilometers off Vietnam's central coast, will any of Hanoi's long list of partners give more than lip service to Vietnamese protests?

For Hanoi, difficult choices

News of the deepsea drilling rig's deployment broke on May 4, when a Vietnamese Foreign Ministry spokesman reacted to a routine warning to mariners issued by China's Marine Safety Administration. A map provided by the state oil company, PetroVietnam, showed the CNOOC vessel to be about 34 km south of Triton, the southwestern-most of the Paracel Islands group, and 221 kilometers due east of Ly Son Island (ironically the home port of the Vietnamese fleet that has for several hundred years fished the waters of the Paracels).

Haiyang Shiyou 981's deployment is "illegal and worthless" declared the Vietnamese spokesman, adding that the site is squarely on Vietnam's continental shelf.

Not so, says Beijing. The drilling site is "completely within the waters of China's Paracel Islands."

Hanoi rejects China's claim to sovereignty over the Paracels, a group of islets and reefs that sprawl across the sea south of Hainan Island and east of central Vietnam. Beijing ejected garrisons stationed on several of the Paracels by the Republic of Vietnam (the former Saigon regime) in 1974 and since then it has exercised increasingly tight de facto control over the archipelago and adjacent waters.

The Paracels are not sufficiently consequential to extend China's exclusive economic zone, according to the UN Convention on the Law of the Sea. However, any rock that stays dry at high tide can "generate" territorial waters out to 12 nautical miles from its shore. The drilling site is 18.5 nautical miles from Triton Island. Thus it would not fall within "Chinese waters" even if Beijing's claim to the Paracels were deemed valid.

According to Chinese reports, the 31,000 tonne, US$1 billion CNOOC drilling rig will remain at the site until August. Launched in 2011, Haiyang Shiyou 981 has reportedly been until now drilling exploratory wells offshore from Hong Kong. The rig is capable of drilling into the seabed at depths of up to 3,000 meters. Vietnamese maps indicate that the new drilling site is less than 1,000 meters beneath sea level.

Also according to Chinese media on May 6, Vietnamese marine police vessels were already "interfering" with the operation of the rig. Beyond doubt, Chinese coast guard vessels are also close at hand. Both nations can deploy considerable naval and air assets to back up their paramilitary forces.

The Haiyang Shiyou 981's deployment thus poses an agonizing dilemma for Hanoi. Like Chinese interference three years ago with Vietnamese oil and gas survey vessels, China's offer to auction off exploration blocks in Vietnam's EEZ and its sometimes successful efforts to intimidate foreign oil firms, this latest provocation threatens not just humiliation but also real economic damage.

Unlike the Philippine military, Vietnam's armed forces are a credible deterrent. No one doubts the courage or discipline of Vietnamese soldiers and sailors, heirs to a millennium of successful resistance to invading armies, particularly Chinese ones. Further, Hanoi has put serious effort into air and naval force modernization in recent years. They are capable of going a few, perhaps several, rounds with the Chinese.

China seems all too hopeful of humiliating Hanoi or, alternatively, of provoking the Vietnamese to attack. Its pursuit of hegemony in the South China Sea, aptly characterized as a "talk and take" strategy, has been intoxicatingly successful so far. Beijing seems intent on impressing world opinion, not on deferring to it. Egged on by populist media, its citizens are spoiling for a fight.

The deployment of the Haiyang Shiyou 981 has created an ugly situation, one that easily escalate into a shooting war. Only Beijing can unwind it -- and only if it cares to.