Douglas Paal, vice-president for studies at the Carnegie Endowment for International Peace, said it is helpful for the two militaries to meet in the South China Sea area, so forces can humanize their views of each other.

But he pointed out that it is more likely the drill is occurring there because the weather is reliably compliant compared to points further north.

"These exercises are all about instilling a degree of trust. For the US side, moreover, HA/DR is acceptable to Congress, when other forms of exercise might imply too much trust,"Paal said."At this stage of the US-China military rapprochement, it seems about right and welcome."

"It is welcome that the US and China are pursuing more military exercise. Perhaps China's agreement to conduct this drill in the South China Sea signals that Beijing sees the US as having a legitimate role to play in those waters. If so, it would be a positive message," said Bonnie Glaser, senior adviser for Asia at the Center for Strategic and International Studies.

The joint drill this time came just two months after President Xi Jinping and President Barack Obama concluded more than 20 agreements in Beijing from climate change to military confidence building, injecting renewed optimism in a relationship that has been marred by disputes in cyber security and tensions in South and East China seas.

On the military front, the two leaders signed a memorandum of understanding (MOU) on rules of behavior for safety of air and maritime encounters, and an MOU on notification of major military activities and confidence building measures mechanism.

David Shambaugh, professor of political science and international affairs at George Washington University, said that 2013-2014 witnessed the broadest and deepest set of "mil-mil" exchanges in 25 years, and this new investment needs to be built upon.

"This will require, on the American side, revision or retraction of the 2000 Defense Authorization Act – which places a range of restrictions on what the Pentagon can do and not do in its exchanges with the People's Liberation Army," he wrote on the China-US Focus website."The US and Chinese militaries are at the heart of strategic interactions between the two nations, and all efforts must thus be made to deepen the interactions and communications between the two military establishments."

Zhu Bo, an honorary fellow with the Center of China-American Defense Relations at PLA Academy of Military Science, described the beauty of the MOU as being "tactical, more than strategic".

"At present, there are quite a few mechanisms between the two militaries, such as Defense Consultative Talks, Defense Policy Consultative Talks, Strategic Security Dialogue and a hotline, but they are all at strategic levels whereby only strategic issues are discussed by the two sides," Zhu wrote in the China-US Focus.

He said rules of behavior for safety of air and maritime encounters are tailor-made for officers, sailors and airmen from both sides. "It is them who deal with one another every day," he said.

But Zhu said that the MOU won't be able to resolve a strategic issue – lack of sufficient trust between China and the US, adding that China will not "legalize" US military activities in China's Exclusive Economic Zone.

chenweihua@chinadailyusa.com