Some manned submersibles are equipped to carry ROVs to allow exploration of areas too small or dangerous for direct observation by the submersibles themselves. Transmission of instructions to, and video information from, the vehicle is accomplished by means of an acoustic communication link. 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.

The untethered ROV, more generally called an autonomous underwater vehicle (AUV) or an unmanned undersea vehicle (UUV), eliminates the cable and carries its own power. 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. There are two basic types of unmanned submersibles. In recent years, it has become clear that special purpose, unmanned submersible vehicles can augment or replace manned submersibles. The modular construction of some vehicles permits easy modification of them for different operational tasks. Manned submersibles also have a crew compartment within a pressure hull and life-support systems. Some also have mechanical arms (manipulators) to collect samples and perform other modest tasks outside the vessel. All contain power sources and one or more sensors, among them lights, photo and video cameras, sonar hydrophones, instruments for measuring environmental parameters, side-scanning sonars, and geophysical devices (magnetometer, acoustic profiler, gravimeter).

Submersibles are constructed in a variety of sizes and shapes and are designed to perform different and often highly specialized tasks. Development of a great variety of submersibles during the later 1950s and 1960s came about as a result of improved technology and in response to a demonstrated need for the capability to visit the ocean depths to make direct observations and measurements, to recover lost equipment, and for possible rescue activity. Submersible, small, mobile undersea research vessel capable of functioning in the ocean depths.

Remotely operated vehicle