Possible Clues:

• Sonar, an echo-sounder
• Early form of sonar used to detect submarines
• Echo sounder
• Echo-sounder, early form of sonar
• British term for sonar
• Ultrasonic detector
• It once sounded like Little Richard, we're told
• An early form of sonar, an echo sounder
• Sonar, formerly a way of detecting low tars?
• Early echo-sounder; a disc (anag.)