There's over three minutes of Modern Warfare 3 multiplayer footage below in a new trailer focusing on the game's weapon progression.
Infinity Ward says the video will help you grasp "how MW3 evolves gun progression with its new weapon ranking system."
It adds: "The new progression system is designed to improve specific weapon leveling unlocks (camo, attachments, reticles etc.), and features new weapon proficiencies. Proficiencies allow players to specialize their weapons with new attributes (some unique to specific weapon classes)."