Successfully complete one of the following tasks in an online game to unlock the corresponding medal:

Bronze Star: Get 1,000 kills
Combat Medical Badge: As a medic, save the lives of three teammates
Distinguished Service Cross: Get five hours of playing online
Delta Cross: Get ten knife kills
Hill Giant Medal: Get 10 minutes on Hill
Headhunters Medal: Get five headshots
Infantry Badge: Get 50 kills
Purple Heart: Get saved five times by a Medic
Meritorious Service Medal: Win 10 out of 20 games