British sailor heading west for port city (4)
I believe the answer is:
baku
'for port city' is the definition.
(port in Azerbaijan)
'british sailor heading west' is the wordplay.
'british' becomes 'uk' (Great Britain).
'sailor' becomes 'ab' (abbreviation for able seaman).
'heading west' is a reversal indicator.
'uk'+'ab'='ukab'
'ukab' reversed gives 'BAKU'.
(Other definitions for baku that I've seen before include "Capital of Azerbaijan on shore of Caspian Sea" , "Capital city of Azerbaijan" , "Caspian Sea port" , "Azerbaijan's capital" .)