A group of planes RAF sent up to show weapons (7)
I believe the answer is:
arsenal
'weapons' is the definition.
(I've seen this before)
'a group of planes raf sent up' is the wordplay.
'a group of' indicates a hidden word (group of letters from the clue).
'sent up' says the letters should be written backwards.
'lanesra' can be found hidden inside 'planes raf'.
'lanesra' in reverse letter order is 'ARSENAL'.
'to show' is the link.
(Other definitions for arsenal that I've seen before include "Gunners of North London" , "Armoury - London football club" , "English football club and military depot" , "gunners, so-called" , "Munitions store and English football team" .)