Mission leading to manoeuvres round end of battle (10)
I believe the answer is:
Here is my best explanation:
'mission' is the definition.
('delegation' can be a synonym of 'mission')
'leading to manoeuvres round end of battle' is the subsidiary indication.
'manoeuvres' indicates anagramming the letters.
'round' indicates putting letters inside.
'end of' indicates one should take the final letters.
The final letter of 'battle' is 'e'.
'leadingto' anagrammed gives 'dlegation'.
'dlegation' enclosing 'e' is 'delegation'.
(Other definitions for delegation that I've seen before include "representative group" and "Passing over".)