While on the water, launching an attack (9)

I believe the answer is:

assailing

'launching an attack' is the definition.

'while on the water' is the wordplay.
'while' becomes 'as'.
'on the water' becomes 'sailing'.
'as'+'sailing'='ASSAILING'

(Another definition for assailing that I've seen is " What pirates may be doing".)

I've seen this clue in The Telegraph.

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