British island protected by French vessel on American body of water (6,3)
I believe the answer is:
tasman sea
'body of water' is the definition.
'tasman sea' can be an answer for 'water' (I've seen this before). I'm unsure of the 'body of' bit.
'british island protected by french vessel on american' is the wordplay.
'british island' becomes 'man' (Isle of Man).
'protected by' is an insertion indicator (inserted letters are held or protected).
'french vessel' becomes 'tasse' ('cup' in French).
'on' is a charade indicator (letters next to each other).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'man' placed inside 'tasse' is 'tasmanse'.
'tasmanse'+'a'='TASMAN SEA'
Can you help me to learn more?
(Other definitions for tasman sea that I've seen before include "The main" , "large quantity of water" , "Body of water separating Australia and New Zealand" , "part of Pacific" , "an arm of the Pacific" .)