Debug menu: At the title screen, quickly press Up, Down, Left,
Right, Down, Down, Right, Right, Square. If you did the trick
correctly, you hear a chime and a debug menu screen appears.
Among the options are a level select, CD/sound test, and credits.
Invincibility: Start a game, and press Start and Select. Choose
to abort the mission to quit the game. Then, at the title screen,
press Up, Up, Up, Down, Down, Down, Right, Right, Triangle. If
you did the trick correctly, you hear a chime. Start a new game,
and your tank is now invincible.