Related Clues:

• Mine countermeasure
• Nautical ancestor of GPS
• Sub's navigation
• Submarine navigation device
• Sub-way map?
• Bat's echolocation system
• Part of the garrison - a regiment tracking subs
• Batty navigation aid
• One method of locating schools
• Sub feature
• Ocean floor mapping aid
• Salvager's device
• Nautical equipment led sailor the wrong way
• Bathymetry tool
• Old ship-locating system