Electrical unit army management prescribe at the outset (3)
I believe the answer is:
amp
'electrical unit' is the definition.
(unit of electrical current)
'army management prescribe at the outset' is the wordplay.
'at the outset' indicates taking the first letters (the outset is the beginning).
The first letters of 'army management prescribe' is 'AMP'.
(Other definitions for amp that I've seen before include "Current; hi-fi kit" , "measure of power" , "Sound-boosting piece of equipment (abbr)" , "Certain amount of power" , "Unit of electricity, in short" .)