Assistant's proposal, sending head of army to front (4)
I believe the answer is:
aide
'assistant's' is the definition.
(aide is a kind of assistant)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for aide that I've seen before include "Adviser or assistant" , "a help" , "someone in assistance" , "One to assist" , "Political assistant" .)