Enter any of these codes during gameplay. You will hear a sound effect if the code is entered correctly:

Effect - Code

10 extra Tokens - X, B, X, B, Black
Unlock Ultra Hard Difficulty - X, B, A, X, Black
God Mode - Y, A, X, B, Black
Big guns (1000 points damage per shot) - B, X, A, B, Black
$5000 cash money - A, Y, A, Y, Black
Unlock all planes - Y, X, B, Y, Black