Bomb a military vehicle (4)
I believe the answer is:
tank
I believe this is a double definition.
'bomb' is the first definition.
(both can mean to fail)
'a military vehicle' is the second definition.
(tank is a kind of military vehicle)
(Other definitions for tank that I've seen before include "Large storage chamber" , "Armoured vehicle; large container" , "Vat" , "One has gun" , "Cistern - armoured vehicle" .)