Related Clues:
- GPS precursor
- Radio-based navigational system
- Sub navigation tool
- Relative meets artist coming back for listening device
- Torpedo detector
- Shipwreck locator
- Echolocation
- Hydroacoustic device
- Help in finding objects on a river bed
- Method for detecting submarines
- Navigating system
- Fish-finding device
- U-boat finder
- Submarine device
- Tracking system