Updated 08-19-2015 09:16 PM
This achievement is easier than it sounds, despite what skill or lack of you think you might have.
As a passenger in each vehicle type, get a kill. Much easier, eh?
In the jeep, use the grenade launcher or .50cal turret and kill.
In the tanks, use the mounted turret.
In the boat, use the grenade turrets.
In a heli, be the gunner.
Doing it this way is cake walk and can be done in one round easily.
Also, while in the road vehicles, and even the boat I suppose, just run over an enemy to kill 'em. That works too!