Autonomous underwater vehicle. See also the tags ugv & uav.

Autonomous underwater vehicle.

From the Wikipedia page:

An autonomous underwater vehicle (AUV) is a robot which travels underwater without requiring input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes non-autonomous remotely operated underwater vehicles (ROVs) – controlled and powered from the surface by an operator/pilot via an umbilical or using remote control. In military applications AUVs more often referred to simply as unmanned undersea vehicles (UUVs).

Note that:

If the tags & start to be used, then they should probably be considered synonyms of .