Escape group of ships, briefly (4)
I believe the answer is:
flee
'escape' is the definition.
(I know this)
'group of ships briefly' is the wordplay.
'group of ships' becomes 'fleet' (eg a naval fleet).
'briefly' means to remove the last letter.
'fleet' with its last letter removed is 'FLEE'.
(Other definitions for flee that I've seen before include "Run (from danger)" , "Leave" , "Run quickly away" , "Abscond" , "Turn tail" .)