9 ELECTROACOUSTIC SYSTEMS; NAMELY, SONAR AND DOPPLER SENSOR, DEPTH SOUNDERS, DOCKING UNITS, NAVIGATIONAL AIDS; NAMELY, DOPPLER SONARS, AND UNDERWATER TELEPHONES; THERMISTORS, OVERCURRENT PROTECTORS, OVERTEMPERATURE PROTECTORS, TEMPERATURE COMPENSATION CONTROLS; THERMISTOR PROBES AND PARTS THEREFOR; ACTUATORS; INSTRUMENTS TO MEASURE, CONTROL AND RECORD PRESSURE, TEMPERATURE FLOW AND LEVEL OF FLUIDS