The best map to do all of these is on the Oasis map, preferably while attacking. For the jeep, you can run people over when they are running to their next base, or you can go by the small building before the first base and use the gun attached. For the tank, preferably the heavy tank, you can shoot people in lighter tanks or jeeps. For a jeep, this takes 1 shot, light tank 2 shots.
For the boat, when in the Suburbs area, there is the river by the main road in the area, enemies are usually within the area as the gold crate is in the area also, so using the turret on the boat should get this and maybe a few more kills as well.
The helicopter is the hardest to get with but this can also be done on the same map. When attacking from the start, behind the fencing is a helicopter, you can be the gunner or the missile shooter. Aim near vehicles as the enemy will aim to drive quickly to avoid the heli but this is a bigger threat.
This doesnt have to be in this order and once you do the 4th and final kill, the achievement should pop up