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Playstation 2 - Thunderstrike - Operation Phoenix cheats

Level select
Go to the options. Change the "Vibration" to 1 and "Music" and 
"Sound Effects" to zero. After, hold L1 + L2 + R1 + R2 + Circle + Square.
If the code is accepted, you will see a message.

Unlock bonus helicopters and "Maniac" difficulty mode:
Finish the game in hard mode

Additional bonus helicopter with more armor:
Finish the game in "Maniac" mode