Van on railway. The most dangerous position (5,4)
I believe the answer is:
front line
'position' is the definition.
(I know that front line is a type of line)
'van on railway' is the wordplay.
'van' becomes 'front' (van can mean the front part of something).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'railway' becomes 'line' (line is a kind of railway).
'front'+'line'='FRONT LINE'
'the most dangerous' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for front line that I've seen before include "sharp end" , "Where the fighting takes place" , "Most advanced troops" .)