Take field supplies in a C-47, LVT, M3 or SDK. You must bring supplies from another field that has a spawn into the field that you are trying to resupply and the field you are coming from must have supplies available.
1 - You can either drop the supplies or land and drop them on the air field from the C-47.
Fly from a field that is close by. Slow to less than 200 mph, make sure you're more than 800 feet in the air above the ground. IE if the field is at 3000 feet you must be at 3801 feet. Open the door using the "O" key and hit the drop button as if you were dropping a bomb. Make sure you are over the base when you do this. Or you can simply land the C-47 at the field that you want to resupply open the door and drop them on the runway/concrete (if at a V-base) once you have come to a complete stop and you are on your landing gear, no belly slides.
2 - You can also use an LVT, M3 or SDK.
Up from another field that has a V spawn to the base that you are trying to resupply and make sure that base has supplies available. Drive to the field that you want to resupply and drive onto the concrete anywhere on the base. Open the door on the vehicle, come to a complete stop and drop the supplies on the concrete.
TOE