Special Headset Commands
Say these commands into the headset during gameplay to trigger the corresponding team actions:

"Bravo defuse bomb": Put your crosshairs on the bomb and say this to... you guessed it... defuse the bomb.
"Bravo open door": Same idea. Point crosshairs at door and speak.
"Breech, bang, clear": Point your crosshairs into an open room and your team will throw grenades inside.
"Hands up, get down": Sneak up behind an enemy and yell this, and guess what?
"Team low profile": Your crew will go into stealth mode.

Unlock Level Select
Beat the game on Lieutenant JG difficulty to unlock level select.

Unlock New Difficulties
Unlock the following difficulties by completing the corresponding tasks:
Lieutenant JG: Beat game on Ensign difficulty
Lieutenant: Beat game on Lieutenant JG difficulty
Lieutenant Commander: Beat game on Lieutenant difficulty
Commander: Beat game on Lieutenant Commander difficulty
Captain: Beat game on Commander difficulty
Rear Admiral: Beat game on Captain difficulty
Admiral: Beat game on Rear Admiral difficulty

Terrorist weapons
Successfully complete the game with a rank of ''Ensign'' to unlock terrorist weapons in the armory in single player mode.

Make Mags. Last Longer
Press R3 anytime during gameplay and your ammo will fill up. You must not let your ammo reach zero or the cheat won't work. Just fire a few shots and reload. It works through the whole game!