One aids evacuation of soldiers up in eastern area (5)
I believe the answer is:
enema
'one aids evacuation' is the definition.
'enema' can be an answer for 'evacuation' (I've seen this before). I'm not certain of the 'one aids' bit.
'soldiers up in eastern area' is the wordplay.
'soldiers' becomes 'men' (men can mean a group of soldiers).
'up' is a reversal indicator (in down clue: letters go upwards).
'in' is an insertion indicator.
'eastern' becomes 'e'.
'area' becomes 'a' (maths abbreviation).
'men' reversed gives 'nem'.
'e'+'a'='ea'
'nem' placed into 'ea' is 'ENEMA'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for enema that I've seen before include "medicine to get you going" , "Procedure for vacating the bowels" , "Fluid injected rectally" , "In the end medical procedure" , "Rectal medicine" .)