a priority. On April 15, 1964 Mizar was reclassified AGOR-11, designed for deep oceanographic search and research, and to be operated by MSTS for NRL. The ship was fitted with a deepsea vehicle (fish), equipped with strobe lights, cameras, sonar, and magnetometer. Her major tasks were to be ocean floor study and service as a floating base for underwater acoustic, chemical, and biological research. The search for Thresher had paused with advent of bad weather in September 1963. Mizar was assigned to the successor search task group, TG 168.1, when it formed May 18, 1974. Mizar's "fish" located the wreckage of the submarine within a few hours of searching. Acoustic navigation system The only means of subsurface navigation locating a search vehicle or other sensors relative to the ship and bottom is by acoustic navigation. Towed deep vehicles may be half a mile from the towing ship and respond to the ship's movements as much as half an hour after that movement. A capability developed at the University of Washington Applied Physics Laboratory was implemented for Mizar. The system, an early implementation of a short baseline acoustic system, is composed of a triangular array of hydrophones on the ship's hull, a transponder on the towed vehicle with an acoustic pulse triggered by a signal over the towing cable, and a sea floor transponder triggered by an acoustic signal from the ship. By using travel times of the signals distances can be computed. A response from the vehicle can be computed for relative position with regard to the ship and that from the bottom transponder is used to find its relative position. The towed vehicles relative position to the ship and bottom is then computed. Research The ship was fitted to perform extensively in ocean science and technology with acoustics an important specialty. Mizar supported scientists from three NRL divisions. The Acoustics Division supported undersea surveillance, fleet sonar systems and studied undersea sound propagation. The Ocean Sciences Division worked in the classical oceanography fields of chemical, physical and biological oceanography and atmospheric studies. Research and development regarding materials and ocean engineering and the ship's searches were under the Ocean Technology Division. As an example of extensive acoustic research with general oceanographic observations included was the ship's work in Operation NORLANT, an acoustic propagation and noise experiment that involved aircraft as well as NRL ships Mizar and and the Norwegian research vessel