Airmen at sea, or soldier at sea (6)
I believe the answer is:
marine
'soldier at sea' is the definition.
(I've seen this before)
'airmen at sea' is the wordplay.
'at sea' indicates an anagram.
'airmen' with letters rearranged gives 'MARINE'.
'or' is the link.
(Other definitions for marine that I've seen before include "Relating to the sea" , "Soldier serving on land and sea" , "seaman" , "Sea-soldier" , "Maritime - seagoing soldier" .)