Lifeblood for every soldier in the trenches (6)
I believe the answer is:
sapper
'soldier in the trenches' is the definition.
'sapper' can be an answer for 'soldier' (I've seen this before). I'm not certain of the 'in the trenches' bit.
'lifeblood for every' is the wordplay.
'lifeblood' becomes 'sap' (I can't explain this - if you can you should believe this answer much more).
'for every' becomes 'per' ('per' means 'for each' or 'for every').
'sap'+'per'='SAPPER'
Can you help me to learn more?
(Other definitions for sapper that I've seen before include "Private in the British Royal Engineers" , "Army engineer" , "Royal Engineer" , "Something that wears down" , "Writer" .)