If you want to know how to unlock weapons in Call of Duty: Modern Warfare 2, you have to arduously go through each weapon class menus and check the details. Some guns start available, others require you to reach a certain class level, and some demand you level up a given gun to an arbitrary level. In Call of Duty: Modern Warfare 2, one of the most confusing aspects for new players to wrap their heads around is how to unlock weapons.