Underwater drones can be used for exploration and military ops

The US unmanned underwater drone seized by the Chinese navy is similar to commercial units that have been deployed by oil companies for underwater exploration and by emergency services for search and rescue, reports say.
The US Navy had used a Bluefin-21 to search for wreckage of Malaysia Airlines Flight 370, descending to 5,000 feet to scour the Indian Ocean floor.
The underwater drone is commercially available and they retail for about USD 150,000, NBC News reported.
These types of gliders are generally used for environmental collection to help the Navy better understand the oceans and how sonar works. They are also used to help the Navy better conduct anti-submarine warfare, it said.

The seized glider belongs to the US Military Sealift Command and was not conducting surveillance, the report said.
The Pentagon has said that USNS Bowditch and the UUV -- an unclassified "ocean glider" system used around the world to gather military oceanographic data such as salinity, water temperature, and sound speed - were conducting "routine operations" in the South China Sea on December 15 when the Chinese navy seized the drone.

The Pentagon said the Chinese navy seized the unmanned underwater drone while it was being recovered by a US Navy oceanographic survey ship. The ship and the drone were conducting routine operations in accordance with international law when a Chinese Navy PRC DALANG III-Class ship launched a small boat and retrieved the UUV, it said.

The Chinese Defence Ministry has said it had taken the drone for verification and accused the US of "making a fuss" over the incident after US President-elect Donald Trump accused China of "stealing" the US Navy research drone.
Defence Ministry spokesperson Senior Colonel Yang Yujun dismissed the US allegations, insisting China had been "professional and responsible" to take the drone.
"We had to examine and verify the device in a bid to avoid any harm it might cause to the safety of navigation and personnel," he said in a statement.