Authoritarian back on ship (5)
I believe the answer is:
stern
I believe this clue is a double definition.
'authoritarian' is the first definition.
(I've seen this before)
'back on ship' is the second definition.
(I've seen this before)
(Other definitions for stern that I've seen before include "Rear end" , "Ship's rear" , "having a forbidding appearance" , "Strict - forbidding" , "Grim; severe" .)