Cheats are unlocked not by inserting passwords, but by acquiring the thirty Intel Pieces strewn throughout the game. The more of them you collect, the more cheats you can access. On the left are the number of Intel Pieces collected, and on the right are the cheats that are unlocked, with an explanation of what each does.

Number of Intel pieces	Unlockable
2 - "CoD Noir"	Play the game in black and white.
4 - "Photo-Negative"	Game colors become inverted.
6 - "Super Contrast"	Game's contrast increases.
8 - "Ragtime Warfare"	The game feels like an old silent movie.
10 - "Cluster Bombs"	One frag grenade thrown equals five in explosion.
15 - "A Bad Year"	Enemies explode into tires when shot.
20 - "Slow-Mo Ability"	Game plays at 40% normal speed.
30 - "Infinite Ammo"	Just what it says.