Thunderstrike: Operation Phoenix
Enter the options screen. Set "Vibration" to "1" and "Sound effects"
and "Music" to "0". Then, hold L1 + L2 + R1 + R2 + Circle + Square.
The message "Spooky Cat" will appear in the middle of the screen to
confirm correct code entry.
Successfully complete the game under the hard difficulty setting.
The maniac difficulty setting and a bonus helicopter and will now
be unlocked. The bonus helicopter flies, turns, climbs, descends,
and shoots faster.
Successfully complete the game under the maniac difficulty setting
to unlock a third bonus helicopter, which you can use on any
difficulty setting. It has the same top speed and fire rate as
the second bonus helicopter, but more armor.