The following special forces units are unlocked at the 'Main' menu by selecting the 'Community & Extras' option and highlighting the 'VIP' selection and pressing the Y button, then entering one of the following codes (without the quotes).
Unlock Russian Spetsnaz Guard Brigade Enter the code 'SPZA39'.
Unlock Special Spetsnaz Battalion Enter the code 'SPZT17'.
Unlock European Enforcer Corps Enter the code 'EUCA20'.
Unlock U.S. Joint Strike Force Enter the code 'JSFA35'.