Splitting up, say, soldiers in depot (12)
I believe the answer is:
segmentation
'splitting up' is the definition.
(putting into segments)
'say soldiers in depot' is the wordplay.
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'soldiers' becomes 'men' (men can mean a group of soldiers).
'in' means one lot of letters goes inside another.
'depot' becomes 'station' (I've seen this in another clue).
'eg'+'men'='egmen'
'egmen' put into 'station' is 'SEGMENTATION'.
(Another definition for segmentation that I've seen is " Division".)