The Pentagon says it has much to learn about the strategic ambitions and decision-making behind Beijing's military modernization. One thing is known though. A decade of sustained economic growth in China has helped the Peoples' Liberation Army to close the weapons technology gap with the United States.

"They have achieved that largely by leveraging success in the commercial sectors in China in ship building, information technologies, and other things that they have then been able to translate back into the military modernization program," said James Mulvenon, a China analyst at the Rand Corporation, a government-funded research institute. He said a recent Pentagon report to Congress on China's military progress, as well as military exercises the U.S. Navy, makes clear that U.S. officials are concerned about Beijing's military program.

"I think that the tone and content of the latest annual report on Chinese military power clearly shows that they are concerned about it and our [military] exercising and other things we are doing in the region shows the seriousness with which we take these developments," added Mr. Mulvenon.

The report concludes the Chinese military has directly benefited from what has been a five-fold increase in the country's economic growth, enabling Beijing to upgrade missiles, aircraft, and submarines, while looking to achieve the same level of technology as the industrialized world within the next five to 10 years.

But the Pentagon's latest assessment of China's military capabilities concludes Beijing is likely to fall short of fully meeting that goal. Richard Bitzinger is a researcher at the Defense Department's Asia Pacific Center for Security Studies in Hawaii.

"The concern is obviously that the Chinese are going to be moving from a military that was largely a 1950s and 1960s technology base to one that is certainly 20-25 years further on down the line," said Richard Bitzinger.

Over the years, China has purchased much of its military upgrades from Russia and countries of the former Soviet Union, which still leaves it far behind U.S. technology.

"It is certainly a much more formidable military than it was even a decade ago and all that of course, at the very least, complicates Pentagon military planning with regard to East Asia and particularly with regard to any kind of possible conflict in the Taiwan Straits," he added.

Several China defense analysts who work closely with or for the U.S. military say the Chinese recently unveiled a more advanced attack submarine that caught U.S. intelligence by surprise.

What does this all mean for the U.S. military? Chinese military officials have described this buildup as defensive. But Retired Admiral Eric McVadon, who was the U.S. defense attaché in Beijing from 1990 to 1992, believes these advances raise questions about Beijing's strategic ambitions, and could directly affect the United States if it ever had to come to the defense of Taiwan, as it is legally bound to do.

"Taiwan is the thing that always comes to mind, where they could essentially accomplish something with respect to Taiwan and present the world with a fait accompli because they had confused, delayed or deterred us for long enough time for that to happen," he said.