Coaster in trouble without a convoy (6)
I believe the answer is:
escort
'a convoy' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for escort that I've seen before include "Protective accompaniment" , "Armed guards" , "Social companion or military guard" , "Go with (someone)" , "Accompany, chaperon" .)