Disclosed is an underwater vehicle that can be operated as a remotely operated vehicle (ROV) or as an autonomous vehicle (AUV). The underwater vehicle has a tether, which may be a fiberoptic cable, that connects the vehicle to a control console. The underwater vehicle has vertical and lateral thrusters, pitch and yaw control fins, and a propulsor, all of which may be used in an ROV-mode when the underwater vehicle is operating at slow speeds. The underwater vehicle may also be operated in a AUV-mode when operating at higher speeds. The operator may switch the vehicle between ROV-mode and AUV-mode. The underwater vehicle also has a fail-safe mode, in which the vehicle may navigate according to a pre-loaded mission plan if the tether is severed.