Or at least it was theoretically the third patrol, since the Pentagon has been rather coy about confirming it happened, and the Chinese have forgone their customary complaints.
China said it was "very displeased" after a U.S. Navy destroyer conducted a so-called freedom of navigation patrol (FONOP) within 12 nautical miles (22 km) of an artificial island built up by China in the South China Sea.
Thursday's operation was the latest attempt to counter what Washington sees as Beijing's efforts to limit freedom of navigation in the strategic waters, and comes as Trump is seeking China's co-operation to rein in North Korea.
China, which claims virtually the entire South China Sea, routinely protests such operations.More news: Key Trump administration figures shaping the North Korea debate
Beijing also said it was "very displeased" with the warship's actions and urged the United States to respect to Chinese sovereignty and security.
The reef is part of the disputed Spratly Islands in the South China Sea, which is the scene of rival claims between China and neighboring countries.
Territorial waters are defined by the UN Convention on the Law of the Sea as extending no more than 12 nautical miles from a state's coastline.
The US does not recognise China's claims to the area.More news: Dolphins rookie Raekwon McMillan injuries knee against Falcons
The Chinese Foreign Ministry has not commented about the escalating crisis on its website, and its regular news briefings are in summer recess.
A spokesman for the Chinese Foreign Ministry, Geng Shuang, said in a statement on its website late Thursday that the passage by the John S. McCain violated Chinese and worldwide law and "did serious harm to Chinese sovereignty and security".
He also insisted that such operations "seriously endanger lives".
"Certain external forces are swimming against the current and continuing to stir up trouble under the pretext of "freedom of navigation, '" Mr. Geng said". USA officials say the military will continue to sail, fly and operate wherever permitted by worldwide law.
The US move came four days after the United States, Australia and Japan denounced Beijing's island-building and militarization of the South China Sea on the sidelines of a security forum of the 10-nation Association of Southeast Asian Nations (ASEAN) in Manila.More news: Migrant rescue boat heading to aid of anti-migrant vessel in Mediterranean
"China is resolutely opposed to this kind of show of force and pushing of regional militarization by the USA that may easily cause an unexpected incident at sea or in the air", the ministry said in a statement.
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