Take a look at all the facts about Submersibles
There are two basic types of unmanned submersibles. The remotely operated vehicle (ROV) is controlled from the surface by a tether, or cable, which is used to transmit power to the vehicle and serve as the medium through which the video signal and other sensor data are transmitted to the surface.
The untethered ROV, more generally called an autonomous underwater vehicle (AUV), eliminates the cable and carries its own power.Because of the drastically reduced bandwidth and transmission delays inherent in tetherless underwater communications, these vehicles roam freely using onboard computers to run preset missions
In addition to salvage and rescue missions, submersibles are used for laying pipelines underwater, for work on offshore oil drilling platforms and wellheads, and for seafloor mapping, underwater surveys, and tunnel and aqueduct inspections.