To enable cheat mode, pause the game while firing and press B, A, B, A, A, A, B, A, B, A, C, X. To make use of your new-found power, enter any of the codes below:

SKIP MISSION: B, A, C, C, A, A, A, X
INCREASE MISSION NUMBER: C, A, A, A, A, C, A, X
SUPER MISSILES: C, A, A, B, A, X
SUPER LASERS: C, A, A, B, A, C, A, X
INVINCIBILITY: A, B, A, C, A, A, B, A, X
SMART BOMB (HITS ENEMIES AROUND YOU): A, C, A, B, A, A, C, A, A, A, X
REFILL WEAPONS: B, A, A, A, A, B, A, X
DISPLAY PLAYER'S NAME: B, A, B, X
DISPLAY PROGRAMMERS MESSAGE: B, A, C, A, C, A, X