Answer:

sonars

Answer	Crossword Clue
SONARS	Navigational tools
SONARS	Echolocation methods
SONARS	Searching systems

SONARS	Echo sounders
SONARS	Sub finders
SONARS	Sub systems
SONARS	Echolocation devices
SONARS	Sub-detecting devices.
SONARS	Submarine "ears."
SONARS	Sound devices.
SONARS	Anti-sub devices

SONARS	Undersea trackers
SONARS	Devices on destroyers
SONARS	Sub detectors
SONARS	Submarine detection systems
SONARS	Finding things?
SONARS	Sub-detecting systems
SONARS	Underwater sound detectors
SONARS	Naval instruments

SONARS	Underwater detection instruments
SONARS	Underwater detection systems
SONARS	They make waves in the ocean