CAM RANH BAY, Vietnam – U.S. Defense Secretary Leon Panetta used a visit Sunday to Vietnam to make clear Washington’s intent to help allies in the Asia-Pacific region develop and enforce maritime rights in the South China Sea, which Beijing largely claims.

On a historic stop in Cam Ranh Bay, the strategic port that was a U.S. base during the Vietnam War, Panetta could gaze out from the flight deck of the USNS Richard E. Byrd and reflect on the significance of the harbor, which represents both a painful past for the American military and a challenging but hopeful future.

“The new defense strategy that we have put in place for the United States represents a number of key elements that will be tested in the Asia-Pacific region,” Panetta told reporters.

He said the U.S. would “work with our partners like Vietnam to be able to use harbors like this as we move our ships from our ports on the West Coast toward our stations here in the Pacific.”

Panetta, the first U.S. secretary of defense to visit the bay in more than three decades, never mentioned China as he spoke to crew members on the Byrd and later to reporters. But he left no doubt the U.S. will maintain a strong presence in the region and wants to help allies protect themselves.

His visit is likely to irritate Chinese leaders who are unhappy with any U.S. buildup in the region and view it as a possible threat. U.S. officials are wary of China’s increased military buildup and expanding trade relations with other countries in the region.