Unlockables

After-Credit Sequences - Beat the game on any difficulty and let the credits run all the way through. When they finish, you'll start another mission. This mission takes place on a plane the resembles Air Force One, wherein you must fight your way through a hoard of baddies, save the V.I.P. and escape the plane in less than 2 minutes.

Also, when you finish the game, you unlock the Arcade Mode.

Unlockable

Air Force One Mission Finish The Game
Arcade Mode Finish The Game

Unlockables Arcade Mode

Arcade Mode To unlock Arcade Mode, beat the game once through on any difficulty level. Arcade Mode itself is split into two options - Full Challenge or Level Chal

Collect All Intel Pieces - Cheats are unlocked not by inserting passwords, but by acquiring the thirty Intel Pieces strewn throughout the game. The more of them you collect, the more cheats you can access. On the left are the number of Intel Pieces collected, and on the right are the cheats that are unlocked, with an explanation of what each does

"A Bad Year" Enemies explode into tires when shot Collect 15 intel pieces
"Cluster Bombs" One frag grenade thrown equals five in explosion Collect 10 intel pieces
"CoD Noir" Play the game in black and white Collect 02 intel pieces
"Infinite Ammo" Just what it says Collect 30 intel pieces
"Photo-Negative" Game colors become inverte Collect 04 intel pieces
"Ragtime Warfare" The game feels like an old silent movie Collect 08 intel pieces
"Slow-Mo Ability" Game plays at 40% normal speed Collect 20 intel pieces
"Super Contrast" Game's contrast increases. Collect 06 intel pieces

Multiplayer Weapons - Unlockable multiplayer weapons are based on your rank you receive. As you gain in rank, you will gain the ability for more and more weapons.

Unlockables

Assault Rifle (G3) Rank 25
Assault Rifle (G36C) Rank 37
Assault Rifle (M14) Rank 46
Assault Rifle (M4) Rank 10
Assault Rifle (MP44) Rank 52

LMG (M60E4) Rank 19

Pistol (Desert Eagle) Rank 43
Pistol (Golden Desert Eagle) Rank 55
Pistol (M1911) Rank 16

Shotgun (M1014) Rank 31
SMG (AK-74U) Rank 28
SMG (Mini Uzi) Rank 13
SMG (P90) Rank 40
Sniper Rifle (Barret) Rank 49
Sniper Rifle (Dragunov) Rank 22
Sniper Rifle (M40) Rank 04
Sniper Rifle (R700) Rank 34

Using Golden Weapons - Golden weapons are considered as special camo that you obtain when you fully complete their respective weapon challenges. You can use them by choosing that gold camo of the respective weapon. Note: The gold weapons are not enhanced, stronger, or more powerful in any way, it's simply Skin

Unlockables

Golden Ak-47 Complete all Assault Rifle challenges.
Golden Desert Eagle (Not Skin) Reach Lv. 55
Golden Dragonuv Complete all Sniper challenges.
Golden M1014 Complete all Shotgun challenges.
Golden M60 Complete all LMG challenges.
Golden Mini-Uzi Complete all SMG challenges.