France falls behind joint leader of fleet (8)
I believe the answer is:
flagship
'leader of fleet' is the definition.
(I've seen this before)
'france falls behind joint' is the wordplay.
'france' becomes 'f'.
'falls behind' becomes 'lags' ('lag' can be a synonym of 'fall behind').
'joint' becomes 'hip joint' (part of body).
'f'+'lags'+'hip'='FLAGSHIP'
(Other definitions for flagship that I've seen before include "Pre-eminent product" , "leading product" , "Something of the greatest importance (to an admiral?)" , "Most important part of a group" , "Pre-eminent item" .)