Navigational aid the same both ways (5)
I believe the answer is:
radar
This clue is a double definition.
'navigational aid' is the first definition.
(I've seen this in another clue)
'the same both ways' is the second definition.
(Other definitions for radar that I've seen before include "Instrument to detect and locate distant objects" , "waves to expose foe" , "Radio detection system" , "location finder" , "Remote detection system" .)