Target the French ship, it's drifting (7)
I believe the answer is:
aimless
'drifting' is the definition.
('aimless' can be a synonym of 'drifting')
'target the french ship' is the wordplay.
'target' becomes 'aim' ('aim' can be a synonym of 'target'**).
'the french' becomes 'le'.
'ship' becomes 'ss'.
'aim'+'le'+'ss'='AIMLESS'
'it's' acts as a link.
(Other definitions for aimless that I've seen before include "lacking direction" , "With no plan or programme" , "Haphazard" , "Lacking ambition or target" , "Lacking purpose" .)