How do get level 4 on Call of Duty 4?

Answer 1

If you have it on Xbox 360 or PS3 just play online and keep doing online matches till you get to level 4. You get points when you kill someone or send in air strike or helicopter. Air strike is 3 kill streak and I think helicopter is 5 kill streak. If you have been leveled up in the middle of a match online It will say You've been promoted! E.g: Yo've been promoted Gunnery sergernt 1.

Answer 2

You play games of multiplayer to rank up and unlock the challenges. You must then complete the given objectives to complete the challenge e.g. Fall 30ft to your death.

Answer 3

First Level Up Get A New Weapon Go To Barracks Go To Challenges Then You Select which class and you can see every challenge there is.