To achieve that, Hanoi has sought to appease its own generals and enhance national defense through a series of major arms deals with Russia worth billions of dollars. The most notable weapons purchases are six Kilo-class submarines and up to 20 Su-30 fighter-bombers. Hanoi is also busy enticing Russia into its oil and gas industry.

Those moves were quickly followed by a low-level yet historic visit by the USNS Richard E. Byrd, which became only the second U.S. ship to put into a Vietnamese port for repairs. The visit was widely viewed by analysts as a fresh sign of the quiet cooperation emerging from improved relations between the two former enemies.

Taken together, the gestures toward Russia and the U.S. sent a clear and irritating message to Beijing: Even as it displays a rapidly growing assertiveness, China should not take its territorial claims in the South China Sea for granted.

China and Vietnam have a love-hate relationship that dates back about 2,000 years and has been sorely tested in the modern era. Both claim the strategically important and mineral-rich Paracel and Spratly island chains. China is also putting in place its "String of Pearls" strategy, basically a forward line of friendly ports and islands stretching from the South China Sea to the Gulf of Siam, designed to secure an alternative trade route to the all-important Malaccan Straits.

Moves are also afoot for the construction of an oil and gas pipeline across Burma that would enable Beijing to pump Middle East-sourced crude directly into China's backyard, rendering tanker traffic through the straits unnecessary.

In tempering China's expansion efforts, Vietnam's ruling elite are responding to a constituency on which it depends for its political survival -- the Vietnamese military.

"The military remains a powerful force in Vietnam, and the Communist Party of Vietnam (CPV) must respect its concerns," said Gavin Greenwood, a regional security analyst with Hong Kong-based Allan & Associates.

Nevertheless, the pro-China faction within the senior ranks of the CPV remains strong and pragmatic, and fully recognizes the economic gains Vietnam stands to make by trading off the commercial coat tails of its much larger and richer northern neighbor. Total two-way trade between the two countries is expected to top $25 billion in 2010 alone. 

But Vietnam's trade deficit with China remains massive, reaching $11 billion last year, due to the type of goods Vietnam offers for export. Vietnamese officials complain that these are mainly restricted to agricultural products and minerals -- in other words, the lower end of the supply chain.

Others see such numbers as damning evidence of China's unwanted dominance.

"Critics . . . see the government as betraying the sacrifices of the past in exchange for economic gains they argue bring Vietnam no lasting benefit," said Greenwood.

Anti-Chinese sentiment rose sharply in 2007, when the government awarded a major contract to the Chinese resources group, Chinalco, to develop a bauxite mine in the Central Highlands.

Among the critics was Gen. Vo Nguyen Giap. As the chief military planner in the victory over the French colonial forces at Dien Bien Phu in 1954 and in the war against the U.S. that ended in the unification of North and South Vietnam in 1975, Giap is a rare force in Vietnamese political life. Even the country's most powerful man, CPV General-Secretary Nong Duc Manh, who heads the party's pro-China faction, must occasionally bow to Vietnam's illustrious living legend.

Giap has led a chorus of veterans in accusing the government of selling out to Beijing -- and to capitalism. That chorus is growing louder ahead of next year's CPV Congress. The 11th five-year congress will set party policy on a stage built for future leaders, giving them an opportunity to vent mounting frustrations over China's influence within Vietnam's fiercely independent borders.

Manh is well-aware of this, and Greenwood said the timing of the Russian arms deal may reflect domestic political concerns more than any external military threat.

The surge in defense spending a year ahead of the Congress, he said, particularly for a weapons system that appears directed at countering Chinese military power in the region, would be seen in Hanoi's China-friendly circles as a small price to pay for appearing to stand up to Beijing -- regardless of the economic and military realities.

It's a tactic that Vietnam used often during the Cold War, but with an added twist: the idea of a U.S. return to Cam Ranh Bay, the highly strategic deep-water port established by the Americans during the Vietnam War. As U.S. Pacific Commander Adm. Robert Willard recently told the U.S. Congress, U.S. military ties with Vietnam are continuing to improve. 

Carl Thayer, a veteran regional military analyst at the Australian Defence Force Academy, says that Vietnam's attempt to engage both sides is a delicate balance to strike. Vietnam and China just conducted their ninth joint patrol in the Gulf of Tonkin, and also conducted their first joint search and rescue operations.

"Vietnam just held its high-level political-military security dialogue with the U.S.," Thayer pointed out, "but prior to that received a senior [People's Liberation Army] officer."

Vietnam's pro-China faction does not object to economic or commercial relations with the U.S., Thayer said, adding that the U.S. ships that had made port calls were non-combatants.

However, the U.S. has also raised the possibility of signing an Acquisition and Cross Service Agreement (ASCA) with Vietnam for reciprocal logistical support, supplies and services. Such an agreement is normally drawn up between the U.S. and its allies or coalition partners.

Thayer said the pro-China faction, and China itself, would have its concerns if these ship repairs became a permanent feature on Vietnam's naval horizon.

"Beijing," he said, "would draw the worst-case conclusion."

**Luke Hunt is a Hong Kong-based correspondent and a World Politics Review contributing editor.