Weapons, Attachments and Blueprints\n\n All Modern Warfare 2 weapons will be available for everyone in Modern Warfare 3 but you need to complete each weapon's unlock challenge in Modern Warfare 2 before you can get it in 3.
It's worth noting that while this is a standalone game, it does offer some connections and references to its predecessor, Modern Warfare 2, in terms of story continuity and characters. However, having played or owning MW2 is optional for playing or enjoying MW3.