Crossword Genius

Make a ship unfit to carry out an attack (6)

Ross

I believe the answer is:

assail

I'm a little stuck... Click here to teach me more about this clue!

'an attack' is the definition.
(I've seen this before)

'make a ship unfit to carry out' is the wordplay.
I cannot quite understand how this works, but
'a' is found in the answer.
'ship' could be 'ss' and 'ss' is found in the answer.
The remaining letters 'ail' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for assail that I've seen before include "Aggressively attack" , "Make violent attack on" , "Trouble" , "Go for" , "Molest or harass" .)

I've seen this clue in The Globe and Mail.
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