Unmanned Underwater Vehicle
The underwater equivalent of an unmanned aerial vehicle, an Unmanned Underwater Vehicle is a submarine or smaller vehicle, which has no crew aboard, and is fully or partially under remote human control. It may be capable of autonomous operation during parts of its mission.
There are commercial, scientific, and military applications for UUVs, which are also called Remotely Operated Vehicles (ROV); the ROV terminology is often used for such things as steerable remote camera platforms used to inspect underwater cables, pipelines, and other construction.
While there are expendable UUVs, they are not equivalent to torpedoes or other precision-guided munitions (PGM) that are expected to destroy themselves against targets. A UUV may, however, release PGMs.