Abstract: The location of a tethered undersea vehicle is determined by functionally operating elements on the vehicle, the end of a main cable and a support ship. An acoustic signal is projected from the distal end of the main cable and is received by several hydrophones carried on the vehicle. Frequency multiplexing the time deployed or different phases of the received acoustic signal and transmitting them back to the support craft, permits a processing of the multiplexed signals. This processing gives a visual indication of the vehicle's location with respect to the end of the cable. Since ocean currents can cause a catenary effect in the main cable as it hangs in several thousand feet of water, or the support ship might drift off-station, the tethered vehicle cannot be pulled away from an object of interest on the ocean's floor.