Soldiers in depot moved missile (7)
I believe the answer is:
torpedo
'missile' is the definition.
(missile from a submarine)
'soldiers in depot moved' is the wordplay.
'soldiers' becomes 'OR' (Other Ranks).
'in' means one lot of letters goes inside another.
'moved' is an anagram indicator.
'depot' is an anagram of 'tpedo'.
'or' put inside 'tpedo' is 'TORPEDO'.
(Other definitions for torpedo that I've seen before include "attack" , "Explosive underwater projectile" , "Trooped (anag.)" , "Naval missile" , "Sub's missile" .)