Here are a few clues on how to unlock modes and weapons from “Call of Duty 4: Modern Warfare” on the Xbox 360.

Unlockable: Prestige Mode

To unlock Prestige Mode, which is a multiplayer-only mode, you must reach experience level fifty-five. Instead of capping out at level fifty-five, which is the highest level, Prestige Mode allows you to start again from level one. This can be done a total of ten times, giving you ten different icons in in-game lobbies to show your extreme achievement.

Unlockable: 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 Challenge - that add extra re playability to the game.

Unlockable: New Mission

To play an all-new mission, which is an extra mission after the main quest is completed, beat the game and view the ending credits thereafter. After they’ve run their course, you will then be given the opportunity to play one last single player mission before all is said and done.

Unlockable: Multiplayer Weapons

To unlock the following weapons in multiplayer mode, reach the numbered rank listed.
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