Unlockables:

Multiplayer Characters

N. Africa Terrorist:
Beat the North African mission.

N. Africa Terrorist Ghillie Suit:
Beat the North African mission on Commander or higher difficulty.

N. Africa SEAL:
Beat the training mission.

N. African SEAL Ghillie Suit:
Beat the North African mission on Commander or higher difficulty.

European SEAL Ghillie Suit:
Beat the Polish mission on Commander or higher difficulty.

European Terrorist Ghillie Suit:
Beat the Polish mission on Commander or higher difficulty.

S.E. Asia Terrorist:
Beat the Southeast Asian mission on Captain or higher difficulty.

S.E. Asia Terrorist Ghillie Suit:
Beat the Southeast Asian mission on Commander or higher difficulty.

S.E. Asia SEAL:
Beat the Southeast Asian mission.

S.E. Asia SEAL Ghillie Suit:
Beat the Southeast Asian mission on Commander or higher difficulty.

Weapons: (beat the single-player mode on the following difficulties to earn new weapons)

Ensign:
SEAL Weapons

Lieutenant:
Terrorist Weapons

Commander:
SBS Weapons

Captain:
GROM Weapons

All Difficulty Levels:
IW-80 A2 and the STG 77

Weapon Accessories
Beat the single-player mode on Captain or higher to get the Foregrip and Medium Scope accessories.