Vehicle protection in the front line (8)
I believe the answer is:
vanguard
'the front line' is the definition.
(I've seen this in another clue)
'vehicle protection' is the wordplay.
'vehicle' becomes 'van' (type of vehicle).
'protection' becomes 'guard' (I've seen this before).
'van'+'guard'='VANGUARD'
'in' acts as a link.
(Other definitions for vanguard that I've seen before include "Foremost part of advancing army" , "Leading part of an army" , "Group at front" , "Trail-blazer" , "Front of advancing army" .)