Military vehicle’s fuel container (4)
I believe the answer is:
tank
This clue is a double definition.
'military vehicle's' is the first definition.
(tank is a kind of military vehicle)
'fuel container' is the second definition.
(as in a fuel tank)
(Other definitions for tank that I've seen before include "Fighting vehicle" , "Miltary vehicle" , "Container for fish (or soldiers?)" , "Military machine" , "Armoured vehicle; large container" .)