A marine weapon? (3)

I believe the answer is:

arm

'weapon?' is the definition.
('arm' can be a synonym of 'weapon')

'a marine' is the wordplay.
'marine' becomes 'rm'.
'a'+'rm'='ARM'

(Other definitions for arm that I've seen before include "Accoutre" , "5 [BRANCH]" , "Supply weapons" , "Test of strength with elbows on the table" , "Equip with a limb" .)

I've seen this clue in the Evening Standard.

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