The RPG is a weapon from Call of Duty 4: Modern Warfare, Call of Duty: Modern Warfare 2, Call of Duty: Black Ops and Call of Duty: Modern Warfare 3. Contrary to popular belief, "RPG" does not standing for "Rocket Propelled Grenade", but actually "Ruchnoy Protivotankoviy Granatomyot" (Russian for "Hand-Held Anti-Tank Grenade Launcher").
 Modern Warfare
In Modern Warfare, it is equipped through a perk (RPG-7 x2). It is not a popular choice but can be combined with the perk Sonic Boom for high damage and can also take down an attack helicopter with one hit - If you can hit it, of course.
 Modern Warfare 2
In Modern Warfare 2 it is a secondary weapon. It is the weakest of the launchers (ofther than the Thumper) for taking down air-support as it has no targeting - however, unlike the Stinger is can be free-fired, and unlike the AT4-HS, it has two rockets as opposed to one. Therefore, it is a popular choice with those who want a launcher to kill other players.
 Black Ops
Like Modern Warfare 2, it is the weakest launcher (apart from the China Lake for destroying air support. However, it is useful against infantry.