Part of USMC
I believe the answer is:
marine
'part of usmc' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for marine that I've seen before include "Soldier associated with a navy" , "Relating to shipping or naval matters" , "'Nautical, maritime (6)'" , "Soldier-sailor" , "Concerned with the sea" .)