Vessel overturns in this vehicle (3)
I believe the answer is:
bus
'this vehicle' is the definition.
(bus is a kind of vehicle)
'vessel overturns' is the wordplay.
'vessel' becomes 'sub' (sub is a kind of vessel).
'overturns' says the letters should be written backwards.
'sub' back-to-front is 'BUS'.
'in' is the link.
(Other definitions for bus that I've seen before include "Coach" , "Road vehicle able to carry many passengers" , "Mode of public transport" , "Something caught" , "Public service vehicle" .)