"USS Mustin received the vehicle for the U.S. in international waters approximately 50 nautical miles northwest of Subic Bay," said Cook. The location where the transfer happened was very close to where the Chinese vessel had seized the drone.
Cook described the underwater drone as "a sovereign immune vessel of the U.S. Navy which was conducting routine operations in the international waters of the South China Sea in full compliance with international law."
The drone had completed a pre-programmed military oceanographic survey route and was returning to the USNS Bowditch when it was seized by the Chinese vessel. The taking of the drone was conducted in plain sight of the crew of the U.S. Navy oceanographic vessel.
A U.S. defense official said it is believed that the drone remained on the Chinese ship since being intercepted.
Cook labeled the seizure of the drone as "inconsistent with both international law and standards of professionalism for conduct between navies at sea."
The spokesman said the United States had addressed those concerns to China through "through the appropriate diplomatic and military channels, and have called on Chinese authorities to comply with their obligations under international law and to refrain from further efforts to impede lawful U.S. activities."
Over the weekend, the Pentagon announced that "an understanding" had been secured with China for the return of the underwater drone.
Cook said on Monday that discussions with China about the logistics for the transfer of the drone were "ongoing."
The incident occurred in the South China Sea which has become a focal point for China, the United States and other countries in the region.
China has claimed seven reefs in the Spratly Island chain as its own, essentially dredging them into islands. There are also territorial claims over the Paracel Islands located east of Vietnam and the Scarborough Shoal, 200 miles west of the Philippines.
New satellite imagery released publicly by a Washington think tank last week appears to indicate that China has begun placing military defenses on the artificial islands it has built up in the Spratly Islands.