Problem with First World War battle command (7)
I believe the answer is:
summons
'command' is the definition.
(I know that summons is a type of order)
'problem with first world war battle' is the wordplay.
'problem' becomes 'sum' (arithmetic problem).
'with' is a charade indicator (letters next to each other).
'first world war battle' becomes 'mons' (I can't justify this - if you can you should give a lot more credence to this answer).
'sum'+'mons'='SUMMONS'
Can you help me to learn more?
(Other definitions for summons that I've seen before include "orders" , "Order to attend court" , "Legal order" , "Order to appear in law court" , "Call to join" .)