New design for sonar is a crime (5)

I believe the answer is:

arson

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

'is a crime' is the definition.
(I've seen this before)

'new design for sonar' is the wordplay.
'sonar' anagrams to 'ARSON'.
But, I am not sure how this is indicated.

Can you help me to learn more?

(Other definitions for arson that I've seen before include "serious offence" , "Crime involving fire" , "Fire-raising crime" , "Criminal pyromania" , "matchplay, say?" .)

I've seen this clue in The Daily Express.

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