At the main menu, select the "Community & Extras" option, highlight the "VIP" selection, and press Y. Then, enter one of the following codes to unlock the corresponding unit:

European Enforcer Corps - Enter "EUCA20" as a code to unlock the European Enforcer Corps.
Russian Spetsnaz Guard Brigade - Enter "SPZA39" as a code to unlock the Russian Spetsnaz Guard Brigade. - Special Spetsnaz Battalion - Enter "SPZT17" as a code to unlock the Special Spetsnaz Battalion.
U.S. Joint Strike Force - Enter "JSFA35" as a code to unlock the U.S. Joint Strike Force.

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

Communication Officer (5 points): Complete the Voice Command Trainer.
First Command (10 points): Win the Warning Signs mission.
Combat Chain Master (15 points): Defeat Tanks with Gunships, Gunships with Transports and Transports with Tanks.
Impregnable (30 points): Won Finishing Move without any units being defeated.
Veteran (15 points): Win one match in each mode (Conquest, Assault, Siege, Raid).
Road to War (15 points): Complete "Prelude to War" on any difficulty.
World in Flames (20 points): Complete "Prelude to War" on Hardcore.
Weapon Master (10 points): Use Secondary Attack for the first time.
Hardened by War (20 points): Win 15 missions in the Solo Campaign.
No Stone Unturned (25 points): Win 5 missions without using Mission Support in "World War III".
Call of Booty (20 points): Win a mission by deploying infantry units only.
Lightning War (20 points): Finish "World War III" in less than 15 turns.
Blitz (20 points): Capture an enemy Capital in only 3 turns in "World War III".
Tour of Duty (10 points): Finish "World War III" on Normal.
True Patriot (20 points): Finish "World War III" on Expert.
Ready for Theater of War (30 points): Finish "World War III" on Hardcore.
OpFor (40 points): Finish "World War III" with all 3 Factions on Hardcore.
Training Simulator (10 points): Play 20 Single Player Skirmish matches.
Together We Stand (20 points): Win 10 2 vs. 2 multiplayer Skirmish matches.
Always Attack (15 points): Win 3 missions in a row in Theater of War.
Role of Honor (20 points): Win 30 missions without killing a unit in Theater of War.
Urban Operations (20 points): Play 30 missions in Theater of War city maps.
Breach and Clear (15 points): Disarm 10 minefields in Theater of War.
Survivor (20 points): Have one unit fight and survive for 10 missions in Theater of War.
BOOM (20 points): Deploy 20 minefields which successfully damage enemies in Theater of War.
Mass Murderer (5 points): Kill 500 units in Theater of War.
Spearhead (20 points): Win 5 missions in a row on the same territory in Theater of War.
Strategist (20 points): Win a Conquest by securing all Uplinks on a map in Theater of War.
Point of Attack (20 points): Win 40 missions as Attacker in Theater of War.
Dog of War (30 points): Win a Theater of War Phase as each Faction; you must have played as that Faction in 10 missions.
Air Defense (30 points): Intercept 5 incoming Air Strikes with Electronic Warfare.
War is Heck (30 points): Win 5 missions in a row without losing health in Theater of War.
Destroyer (20 points): Destroy 100 Critical Buildings in Theater of War.
Fast and Furious (15 points): Win a mission within 5 minutes in Theater of War.
Total War (20 points): Play 100 2 vs. 2 Theater of War missions.
Command from the Front (20 points): Kill 10 units with the Command Vehicle's sentry units.
Turning Point (20 points): Win a match after the enemy has triggered DEFCON in Conquest.
Field Intelligence (20 points): Upgrade 100 Uplinks in any game mode and any Mission Type.
Assassin (20 points): Kill 15 enemy Command Vehicles.
Total Warrior (20 points): Win 30 missions in any game mode.
Command & Control (30 points): No Uplinks recaptured by hostiles for 10 consecutive Conquest victories.
Adrenaline (20 points): Retake a Critical Uplink within the 3-minute timer in a Siege match.
Sharpshooter (20 points): Kill an enemy troop without being spotted.
Predator (25 points): Defeat 6 hostile units with a single unit.
Do or Die (30 points): Win a Conquest mission by Annihilation after the DEFEAT counter was under 30 seconds.
Untouchable (30 points): Win a Skirmish mission and lose no health.
Angel of Death (20 points): Kill 10 enemy Evacuation Helicopters.
Cleaner (10 points): Kill 30 enemy regular units.
Army of One (20 points): Win 20 1 vs. 1 matches in Theater of War.
Napoleon (20 points): Achieve a 100% Command Rating in one mission in Theater of War.