US navy develops underwater 'tuna fish' robot
18 December 2014 Last updated at 07:33 GMT
The US military has been showing off its latest catch.
It has developed a robot called 'Ghost Swimmer' as part of a project named Silent NEMO.
The drone is designed to look and swim like a real fish moving a tail side to side in the water.
The US Navy said the robot will keep divers and sailors safe when they're gathering information.
It will also replace the use of bottlenose dolphins and California sea lions the Navy currently trains to spot underwater mines and recover equipment, according to reports.
BBC reporter Pia Harold sent this report.