"We registered our objection to the illegal seizure of a United UUV operating in international waters in the South China Sea. Through direct contact with the Chinese authorities, we have Achieved an understanding that the Chinese will return the UUV to the United States, "Pentagon spokesman Peter Cook said in a statement.
No details were released immediately about how or when it would be returned.
The incident, the latest gathering in international waters in the South China Sea region, occurred earlier this week about 160 kilometres from the Philippine port of Subic Bay.
USNS Bowditch stopped its navigation to collect two submarine drones. At that moment, a Chinese boat that had been following the Bowditch lowered a small boat into the water and the Chinese crew took one of the drones. When the ship the United States warned that the device was his property, he received no response, an American official told CNN.
US oceanographic research ships are usually followed on suspicion that they are spying. In this case, however, the drone was simply measuring ocean conditions, the officer said.
Earlier Saturday, the Chinese Defense Ministry had announced that the Chinese authorities had decided to return the device.
In that announcement, China said the United States had "exaggerated" the issue.
"After confirming that the device was a submarine drone from the United States, the Chinese side decided to transfer it to the United States in the appropriate way," said Chinese Defense Ministry spokesman Colonel Yang Yujun. "China and the United States have maintained communications on this procedure, and it is inappropriate - and hardly useful for a resolution - that the United States unilaterally" exaggerated "this matter.
The statement added that the United States "has been frequently deploying ships and aircraft to conduct military and surveillance operations in waters off China." China strongly opposes such acts and calls on the United States to cease such activities. Of the United States and will take the necessary measures to counteract them ".
China's message came shortly after President-elect Donald Trump got involved in the issue calling China's takeover of the drone as "an unprecedented act."
"China steals a research droid from the US Navy in international waters - takes it out of the water and takes it to China in an unprecedented act," the president-elect wrote on Twitter.