Fast naval ships? (5)
I believe the answer is:
fleet
I believe this clue is a double definition.
'fast' is the first definition.
(similar in meaning)
'naval ships?' is the second definition.
(a fleet of ships)
(Other definitions for fleet that I've seen before include "Ships - quick!" , "Swift like naval force" , "flying?" , "Fast-moving" , "Fast kind of armada?" .)