Fast-moving group of ships (5)
I believe the answer is:
fleet
This clue is a double definition.
'fast-moving' is the first definition.
(fleet can mean fast)
'group of ships' is the second definition.
(eg a naval fleet)
(Other definitions for fleet that I've seen before include "Fast - naval force" , "flying?" , "Rapid in movement" , "Fast kind of armada?" , "Fast as a group of ships" .)