In Mission 9: Battle Of The Bulge, you will be flying an attack plane and have to protect your allied bombers by shooting down enemy planes. There are two total waves of enemy airplanes. The first wave has 8, and the second wave has 12. There are 20 total planes, and you must personally destroy 12 of them to get the "Flyboy" achievement. What makes this kind of difficult is that your teammates also shoot down these planes and do so relatively quickly. You have to be very fast and shoot down as many planes as possible. Press the key to highlight enemy planes. Fly close to them and hold ADS (aim down sights) to target them. Once you have locked on to them, you can speed up to get closer to them, making them easier to hit. It may take a few attempts. There are several checkpoints throughout this and if you are too slow in the beginning, it is almost impossible to still end up with 12 kills. It is recommended to create a manual backup save before this section. When you reach the plane section, pause the game and select "Leave" to go back to the main menu. Then, back up the save file. This allows you to simply copy back the save and not have to go through the entire mission again if you do not get the achievement.