The US Navy is working on a robotic fish that will be able to swim undetected into hostile waters and send back information on opponents' ships.
Project Silent Nemo is under way at a military base outside Washington and navy scientists hope to deploy the robot into the field next year, according to Pilot Online.
The robot fish looks startlingly like a blue fin tuna from a distance and it is almost impossible to tell from its black dorsal fin that it is made of gears and whirring cogs.
The sea drone is 1.5m long and weighs 45kg. It is expected to one day carry cameras and other naval equipment.
Controllers can guide the robot with a video game-style joystick but it can also be programmed to follow a set course.