Worried about vessel (1-4)
I believe the answer is:
u-boat
'vessel' is the definition.
(U-boat is an example)
'worried about' is the subsidiary indication.
'worried' is an anagram indicator.
'about' with letters rearranged gives 'uboat'.
(Other definitions for u-boat that I've seen before include "Sea vessel" , "About (anag)" , "Submersible warship armed with torpedoes" , "German WW 2 sub" , "Take pool exercise" .)