Sound manoeuvre at sea, if in storm, when crossing succeeded (6,2,7)
I believe the answer is:
strait of messina
'sound' is the definition.
(I have seen 'Sound of water' mean 'strait of messina' so perhaps 'sound' could also mean 'strait of messina')
'manoeuvre at sea if in storm when crossing succeeded' is the wordplay.
'manoeuvre' is an anagram indicator.
'when crossing' means one lot of letters goes inside another.
'succeeded' becomes 's' (genealogical abbreviation).
'at'+'sea'+'if'+'in'+'storm'='atseaifinstorm'
'atseaifinstorm' with letters rearranged gives 'straitofmesina'.
'straitofmesina' placed around 's' is 'STRAIT OF MESSINA'.
(Other definitions for strait of messina that I've seen before include "Sound of water" , "waters off Italy" .)