Ship's officer reeling on sub (5)
I believe the answer is:
bosun
'ship's officer' is the definition.
(I've seen this before)
'reeling on sub' is the wordplay.
'reeling' indicates an anagram.
'on'+'sub'='onsub'
'onsub' is an anagram of 'BOSUN'.
(Other definitions for bosun that I've seen before include "Naval officer" , "who controls crew?" , "An abbreviated boatswain" , "Bonus for a small boatswain" , "A diminutive boatswain" .)