Royal Navy is after universal vessel (3)
I believe the answer is:
urn
'vessel' is the definition.
(urn is a kind of vessel)
'royal navy is after universal' is the wordplay.
'royal navy' becomes 'rn'.
'is after' means one lot of letters go next to another.
'universal' becomes 'u'.
'rn' put after 'u' is 'URN'.
(Other definitions for urn that I've seen before include "Huge teapot" , "Pot for human ashes" , "Large pot for making tea" , "Run to get large vase" , "Source of tea" .)