Mid-Atlantic capital (5)
I believe the answer is:
dover
'mid-atlantic capital' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dover that I've seen before include "Be aware of" , "The largest English ferry port" , "White cliffs port" , "Kentish port" , "There'll be blue clouds over the white cliffs here" .)