Mate fires gun from Persian Gulf (3)
I believe the answer is:
pal
'mate' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for pal that I've seen before include "Friend (colloq.)" , "Mate, informal friend" , "Crony" , "China" , "Close friend" .)