Trouble due at sea after head of navy revolted (9)
I believe the answer is:
nauseated
'revolted' is the definition.
(nauseating is a kind of revolting)
'trouble due at sea after head of navy' is the wordplay.
'trouble' is an anagram indicator.
'after' says to put letters next to each other.
'head of' indicates taking the first letters.
The initial letter of 'navy' is 'n'.
'due'+'at'+'sea'='dueatsea'
'dueatsea' with letters rearranged gives 'auseated'.
'auseated' after 'n' is 'NAUSEATED'.
(Other definitions for nauseated that I've seen before include "Revolted" , "Disgusted" , "Sickened" .)