Remotely Operated Vehicles (ROVs) are unoccupied, highly maneuverable underwater machines that can be used to explore ocean depths while being operated by someone at the water surface. These underwater machines are controlled by a person onboard a surface vessel, using a joystick in a similar way that one would play a video game. A group of cables, or tether, connects the ROV to the ship, sending electrical signals back and forth between the operator and the vehicle. Most ROVs are equipped with at least a still camera, video camera, and lights, meaning that they can transit images and video back to the ship. Additional equipment, such as manipulator arm, water samplers, and instruments that measure water parameters, may also be added to vehicles to allow for sample collection. ROV Deep Discoverer (D2) and ROV Seirios are operated off NOAA Ship Okeanos Explorer.