Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Bravery (15 points): Use only your knife to beat the Harbor Level.
Fair Fight (10 points): Reach the mortar without defeating any unarmed soldier in Missile Base.
Good Start (10 points): Complete the Missile Base.
Knife Master (20 points): Complete all levels using only your knife and no powerups.
Mad Marine (30 points): Rescue the POWs twice.
Not Bad (10 points): Get a score of 50,000 or more.
Reflexes (15 points): Complete the Missile Base without dying.
Stamina (15 points): Complete the Bridge Level.
Stealth (15 points): Complete Missile Base, deafting less than 18 enemies.
Teamwork (20 points): Score 200,000 or more playing an Xbox Live co-op match.
True Marine (20 points): Rescue the POWs in less than 10 minutes.
Victory (20 points): Beat the Enemy Prison Camp.