The first confrontation between the US and Chinese navies concluded on Tuesday, when the Chinese returned an underwater oceanographic drone captured in international waters outside of the Philippines.

“The incident was inconsistent with both international law and standards of professionalism for conduct between navies at sea,” said Peter Cook, a Defense Department spokesman.

And President-elect Donald Trump tweeted of the incident, “Let them keep it.”

The drone, composed of about $150,000 in off-the-shelf technology, ranks low on the list of US-China military confrontations — as past confrontations have involved air crews being detained and planes grounded — but it marks an important shift in what is quickly becoming one of the most militarized and fraught regions on the planet.

“It’s a very big deal because it is highly unusual for a Chinese navy ship to confront  US Navy ship, even if an oceanographic vessel,” said Bonnie Glaser, an expert on Chinese foreign and security policy at the Center for Strategic and International Studies.

While the confrontation consisted of a Chinese navy ship plucking the drone out of the sea, the drone belonged to a US Navy ship not far off. This action set a dangerous precedent sure to make US allies doubtful of American commitment to the region.

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