Navy file photo of the T-AGS 60 Class Oceanographic Survey Ship, USNS Bowditch. US Navy WASHINGTON, DC — The Pentagon announced on Saturday that China has agreed to return the US Navy's unmanned underwater vehicle (UUV)that was seized in the South China Sea.

"We have registered our objection to China's unlawful seizure of a U.S. unmanned underwater vehicle operating in international waters in the South China Sea. Through direct engagement with Chinese authorities, we have secured an understanding that the Chinese will return the UUV to the United States," Pentagon spokesman Peter Cook said in a statement.

The UUV was seized while collecting unclassified scientific data about 57 nautical miles northwest of Subic Bay near the Philippines in the South China Sea, US Navy Capt. Jeff Davis, a Pentagon spokesman told reporters on Friday.

"It is ours. It's clearly marked as ours. We would like it back, and we would like this not to happen again," Davis said.

On Thursday afternoon, the USNS Bowditch, which is not a combat ship but does carry some small arms, was stopped in international waters while in the process of recovering a UUV. At that moment, a Chinese ship approached and took the other UUV, Davis explained.

"So much of this doesn't make sense. In fact, almost all of it doesn't make sense," Gregory Poling, director of Asia Maritime Transparency Initiative, a unit of the Center for Strategic and International Studies, told Business Insider.

"That they would just come and swipe a UUV and then head off into the sunset and not say a word is bizarre. It's certainly the most egregious violation of maritime law in recent years," Poling said. "I can't imagine how you would draw a map that would result in this being anything other than the Philippines' EEZ and international waters."

It has been a little over five months since the Hague-based Permanent Court of Arbitration invalidated Beijing's vast territorial claims in the South China Sea. All the while, Beijing has maintained the ruling has no bearing and continues to build on the seven outposts it occupies in the Spratly Islands.