Trooped out a weapon (7)
I believe the answer is:
torpedo
'a weapon' is the definition.
(weapon used at sea)
'trooped out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'trooped' is an anagram of 'TORPEDO'.
(Other definitions for torpedo that I've seen before include "Underwater bomb" , "Explosive underwater projectile" , "Trooped (anag.)" , "American sandwich made with a long split roll" , "fish you want" .)