Vessel carrying a Royal Navy hooter (4,3)
I believe the answer is:
barn owl
'hooter' is the definition.
(I know that barn owl is a type of hooter)
'vessel carrying a royal navy' is the wordplay.
'vessel' becomes 'bowl' (bowl is a kind of vessel).
'carrying' indicates putting letters inside.
'royal navy' becomes 'RN' (abbreviation for Royal Navy).
'a'+'rn'='arn'
'bowl' enclosing 'arn' is 'BARN-OWL'.
(Other definitions for barn owl that I've seen before include "Endangered night bird" , "Flier" , "Large hunting bird" , "Nocturnal raptor" , "Mottled buff and white night bird" .)