Soldiers must carry a blade (3)
I believe the answer is:
oar
'blade' is the definition.
(blade is the word for oar in competitive rowing)
'soldiers must carry a' is the wordplay.
'soldiers' becomes 'or' (Other Ranks).
'must carry' is an insertion indicator (I've seen this in other clues).
'or' enclosing 'a' is 'OAR'.
(Other definitions for oar that I've seen before include "propellor" , "that may be feathered?" , "Bladed pole" , "Pusher" , "I'm involved in row" .)