enter these codes at the password screen
stage 4: medal,medal,your plane,enemy plane
stage 8: your plane,enemy plane,enemy plane,medal
stage 12: bullet,enemy plane,your plane,your plane
stage 16: enemy plane,enemy plane,bullet,enemy plane
stage 20: your plane,medal,bullet,your plane
stage 24: bullet,your plane,medal,medal
stage 28: medal,enemy plane,medal,enemy plane