Destroy the gas station
Survive the pool attack
Call in the airstrike to defeat the Command Center
Watch an unlocked video
Complete the game on Normal Difficulty
Kill 20 enemies with a sniper rifle
Complete a mission on Normal without dying, failing, restarting, or continuing campaign
Kill 15 enemies on the HMV turret
Kill 2 aliens with one Rocket
Complete the game on Hard Difficulty
Unlock all the unlockables
Complete the game on Easy Difficulty
