By 2020, the Chinese navy will have more military vessels than its American counterpart, predicts a U.S. congressional commission on China. An annual report presented to Congress by the U.S.-China Economic and Security Review Commission projected that Beijing's fleet could boast as many as 351 vessels in six years time, a figure that would be larger than current estimates for the American navy.

China's well-documented naval expansion includes a considerable increase in submarines; its number of nuclear submarines is projected to nearly triple between 2000 and 2020. China recently launched its first aircraft carrier. Its unveiling new destroyers as well as amphibious assault vessels. It has developed significant missile capabilities aboard its fleet. Since 1989, the Chinese military's budget has grown by double-digit percentages each year.

The growth of China's navy comes at a time when the U.S. has, according to some critics, conspicuously cut back for budgetary reasons. "Given China’s growing navy and the U.S. Navy’s planned decline in the size of its fleet, the balance of power and presence in the region is shifting in China’s direction," the commission reports.

But that hardly means China is able to match up to U.S. capabilities, particularly given the considerable advantage the U.S. has with its sizable fleet of aircraft carriers and a wide range of other clear technological strengths.

But China's gains are subtly changing the calculus in the region, spurring other regional powers into an escalating arms race. For decades, the U.S. has guaranteed security in the Pacific, but that Pax Americana appears untenable, at least in the long view of China's military strategists.

An expanding Chinese navy may not be a direct challenge to the U.S. But as tensions over disputed islands and waters flare in Asia, it raises questions to what degree Washington is willing to commit itself to allies and check China's advances. Six years from now, let alone six decades, that delicate balance will be all the more precarious.