By Agence France-Presse
The underwater vehicle was taken around 50 nautical miles (90 kilometers) northwest off Subic Bay in the Philippines late Thursday in a non-violent incident, said Captain Jeff Davis, a Pentagon spokesman.
The event unfolded as the civilian-crewed USNS Bowditch was retrieving a pair of "naval gliders" that routinely collect information on water temperatures, salinity and sea clarity.
A Chinese Dalang-III class submarine rescue ship then stopped within 500 yards (meters) of the Bowditch and snatched one of the probes. The Americans safely hoisted the other one back onto their ship.
Davis said he could not recall another time when something like this has happened, and the Pentagon issued a statement calling on Beijing to "immediately" return the probe that it had "unlawfully seized."
The US personnel "were asking over bridge-to-bridge radio to please leave it there," Davis said.
Other than a brief acknowledgment that it had received the message, the Chinese ship did not respond.
"The only thing they said after they were sailing off into the distance was: 'We are returning to normal operations,'" Davis said.
Washington has issued a formal request through diplomatic channels to ask for the probe back.
"It is ours. It is clearly marked as ours. We would like it back, and we would like this not to happen again," Davis said.
Pentagon spokesman Peter Cook said China had acted unlawfully.
"The UUV (unmanned underwater vehicle) is a sovereign immune vessel of the United States. We call upon China to return our UUV immediately, and to comply with all of its obligations under international law," Cook said in a statement.