The CIA ship Hughes Glomar Explorer arrives 40 degrees north, 180 degrees west, at the site of the Soviet K-129 sinking. It positions itself and maintains its position actively through early use of GPS (the first satellites have just been launched). The GPS receiver fills most of a container. Then it begins interrogating a transponder left on the ocean floor next to the submarine at a depth of 5,500 meters. The transponder responds immediately. It is battery-powered and housed in a metal box filled with kerosene to prevent it from being compressed by the enormous pressure.
