The capture of an underwater drone belonging to the U.S. Navy by a Chinese military vessel last week cast a spotlight on the military's growing interest in using such drones.
Here's a look at the incident, what underwater drones do and the challenges they face.
What happened
U.S. officials said the seized drone _ an unarmed torpedo-looking device known as an autonomous underwater glider _ was surveying the ocean floor in the South China Sea and collecting scientific data, such as information on water salinity, when China seized it Thursday. Reports say the captured drone was not one of the Navy's most sophisticated unmanned underwater vehicles.
On Friday, the Pentagon demanded the return of the drone and the U.S. government issued a formal diplomatic complaint.
A day later, China agreed it would return the drone "in an appropriate manner."
Jobs for underwater drones
General military uses for these kinds of drones include stealthily gathering intelligence on opponents, detecting and neutralizing mines, hunting submarines and charting the ocean floor.
But it's not just the military that's increasingly interested in using sea drones. Oil and gas companies want them to inspect rigs, and scientific researchers have also looked to drones to collect oceanographic data.
Technological advancements
Recent advances in autonomy, data transmission and miniaturizing computing power coincide with the military's increased interest in finding ways to integrate unmanned systems into its war planning.
Challenges ahead
Underwater drones face different challenges than their aerial counterparts. For one, communication is more difficult, making it hard for an autonomous vehicle to report information it might pick up underwater.
Drones also need to stay submerged for weeks or months without external help or power. And development of these drones can be complex and costly.
