When you begin your ranking up in Multiplayer or Special Ops, you start in the Enlisted Ranks as a Private I (Level 1).

As a Private, you have a choice between three default loadouts and a limited number of Killstreaks and Field Upgrades. As you gain XP through normal gameplay, you begin to climb through the Enlisted Ranks.

As you continue to gain experience (XP) and advance through the Enlisted Ranks – all the way to Command Sergeant Major V (Level 55) – you'll unlock new weapons, equipment, and perks for your loadouts, as well as Field Upgrades and Killstreaks.

Here are the primary ways to gain XP in Call of Duty: Modern Warfare:

• Completing public Multiplayer Matches, Special Ops Operations, and Missions
• Completing Officer Challenges
• Completing Daily Challenges, which are short objectives that generally take one play session to complete
• Completing Challenge Missions, which are longer, multi-step objectives that also result in other rewards
• Completing Camo Challenges, which unlock variations of base weapon camos and provide XP boosts

In this new progression system, your Enlisted Ranks are never reset, and the functional items unlocked with each rank are never re-locked. Instead of restarting at Level 1, you now progress into the new Officer Rank system.

Officer Ranks is a seasonal ranking system complete with rewards and ranks to progress through. When you reach Officer Rank 1, you receive a cosmetic Weapon Blueprint for your promotion.

Just like the Enlisted Ranks, earning XP progresses you through the Officer Ranks. At each level, you'll unlock a different Officer Challenge, which will reward plenty of XP upon completion and give you a special Seasonal Ribbon.

Earning 10 Ribbons gives you a unique Season Emblem, with each additional 10 Ribbons evolving the emblem. Collecting all 100 Ribbons unlocks an animated Emblem, which serves as proof of getting the ultimate achievement for that season. Reach the maximum Officer Rank, and expect to receive another cosmetic Weapon Blueprint.

Challenge Missions are multi-step objectives that earn you XP bonuses and special rewards for completion. For example, a Challenge Mission may require you to play a specific game mode or use a particular weapon class to complete it.

After you activate a Challenge Mission from the Barracks menu, you'll receive a notification each time you complete an objective and when you complete the entire Challenge Mission.

Defeating enemies with a weapon earns XP for that weapon. After you earn enough XP, the weapon gains a level. Each weapon level unlocks an attachment, a weapon perk, or a camo for that weapon, which you can equip within the Gunsmith.

The camos you earn are the base camo for that weapon. After earning the base camo, a set of Camo Challenges open up, which must be completed to obtain colorful variations within the weapon's camo set. Unlocking camos also earns you XP rewards.