Short-service commission? (6)
I believe the answer is:
errand
'commission?' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for errand that I've seen before include "Short journey to get or bring" , "Chore" , "Native of a former German kingdom" , "Short mission -- ran red (anag)" , "Mission usually for others" .)