Three Planes and Bonus Mission

After you complete level ten, go to the mission select screen, look to the right of the screen, and there will be a tiny airplane. Click on it and there will be a sound to confirm the code. Now you have access to three new aircraft, including the U.F.O., the F-22 Raptor, and the Kikka, a Japenese plane. You will also be able to unlock mission 11, a bonus mission.