The message that reminds you that your ammunition is low & you need to restock, appears in the wrong section.
Currently it shows in battle, after you select your plane , as displayed in the Screenshot.
This is the wrong time and place for the message to appear because you cannot act upon the message immediately.
As the message says, “You can purchase ammunition in the hanger”, however by the time the game ends and you return back to the hanger, you would have forgotten which planes you need to restock ammunition.
There is currently no warnings/symbols on the vehicles that don’t have ammo.
The only way is to check manually in the hanger, where you can see how much ammo you have, if it is low it will be highlighted in red. But this is you physically manually checking for your self.
If you forget or even if you check at start of the day before you play the game, once you play a number of battles at some point you will run out of ammo.
Meaning you will enter a battle with No Ammo. Unfortunately by the time you see the above warning message, it will be too late. You will have to play that game with No Ammo because you won’t be able to replenish your ammo until the game is over and you return back to the hanger.
When you return back to the hanger, like I said before you may forget to reload your ammunition due to the time that has lapsed since you saw the Low Ammunition message.
Then you enter the next battle and either your planes are out of ammo (which ruins your entire game) or you will see the low ammo message again (which only further reminds you that you forgot to reload your ammo after the previous battle).
Hence, The Best Place to show the Low Ammunition message in order to prevent entering battles with Low or No Ammunition is in the Hanger after you press the “To Battle!” Button, but before you actually enter the battle. This is because you can Now Replenish your ammunition if you choose to, because you are still in the hanger.
In addition this will also prevent the message below;
To Conclude, my suggestion will always prevent players from entering battles with Low or No Ammunition.