Unlock all levels and difficulties:
Enter bakersdozen as a profile name.
Unlock Black And White Mode
Beat the game on Easy difficulty to play the game in black and white.
Unlock Infinite Ammo:
Beat the game on Normal difficulty.
Unlock Authentic Mode:
Beat the game on Hard difficulty to play with no checkpoints, no saves, no icons and no reticules.
Unlock Super Squad:
Beat the game on Authentic Mode to unlock the super squad cheat.