Attack the vessel going in, not out
'attack' is the definition.
(thesaurus)
'the vessel going in not out' is the wordplay.
'the vessel' becomes 'urn' (urn is a kind of vessel).
'going in' indicates putting letters inside.
'out' indicates an anagram (out can mean wrong or inaccurate).
'not' anagrammed gives 'ton'.
'urn' placed within 'ton' is 'TURN-ON'.
'attack' is the definition.
(thesaurus)
'the vessel going in not out' is the wordplay.
'the vessel' becomes 'urn' (urn is a kind of vessel).
'going in' is an insertion indicator.
'out' indicates an anagram (out can mean wrong or inaccurate).
'not' is an anagram of 'ton'.
'urn' placed within 'ton' is 'TURN-ON'.
(Other definitions for turn on that I've seen before include "Cause of excitement" , "please" , "Start working" , "Start; become hostile towards" , "Person with twenty five [SEX APPEAL]" .)