Back head of military to do this, perhaps (5)
I believe the answer is:
rearm
'do this perhaps' is the definition.
The definition suggests a singular noun but the answer is not.
'back head of military' is the wordplay.
'back' becomes 'rear' ('rear' can be a synonym of 'back').
'head of' indicates taking the first letters.
The initial letter of 'military' is 'm'.
'rear'+'m'='REARM'
'to' is the link.
(Other definitions for rearm that I've seen before include "Provide with a new supply of weapons" , "prepare for another war" , "Hand new weapons" , "Take weapons again" , "prepare to fight again" .)