Refit gas fitting on warships (8)
I believe the answer is:
frigates
'warships' is the definition.
(frigate is a kind of warship)
'refit gas fitting' is the wordplay.
'fitting' is an anagram indicator (letters fit or arranged differently).
'refit'+'gas'='refitgas'
'refitgas' is an anagram of 'FRIGATES'.
'on' acts as a link.
(Other definitions for frigates that I've seen before include "Ships" , "boats" , "Class of warships" .)