All heroes
Successfully complete the first twelve missions in campaign mode to unlock all twelve heroes as playable characters in quick mission and campaign modes. They include Henry Ramirez, Nigel Tunney, Will Jacobs, Jack Stone, Guram Osadze, Susan Grey, Klaus Henkel, Buzz Gordon, Lindy Cohen, Astra Galinksy, Scott Ibrahim, and Dieter Munz.
Easy mission completion
Use the following trick to complete Missions without doing the objectives. Play the mission like firefight mode. Once you kill everybody, the mission is automatically complete with all objectives done.
Medals
Purple Heart: Get wounded or killed in action.
Bronze Star: Get 15 kills
Silver Star: Get 20 kills
Distinguished Service Cross: Get 25 kills
Congressional Medal Of Honor: Get 30 kills