This is most easily boosted by yourself using a hangar and garage. Any location will work, but I would recommend the
Landsdowne Airstrip in the
Whitetail Mountains, as the hangar and garage are directly next to each, and you automatically unlock a plane upon discovering it.
First, at the hangar spawn a plane with Bombs like the
Pack Hunter,
Carmina or
The Wild Goose. Carpets bombing planes do not count.
Now, take this plane and park it close to a garage. At the garage, spawn ATVs and park them as close of possible to the plane but avoid the propellers. Once the plane has 4 vehicles next to it, get inside, Press LR + RT to drop a bomb and destroy the ATVs, and the plane, unlocking the achievement.
NOTE: If you're having issues with things despawning, try assigning a different Gun for Hire to your roster.