US M72 LAW
The LAW is a rocket launcher, that for some reason doesn't do instant kills. It is still useful in other ways, however. When you fire the LAW, a rocket shoots out in the direction of your crosshair. Once it hits a solid object, an explosion is created with a blast radius larger than that of the M69HE Frag. Any enemy within that area receives 80 damage. The LAW can be very useful for getting rid of campers.
Make sure that you don't fire the LAW at a short range, otherwise you will blow yourself up! A less common known fact is that you can actually shoot down the rocket while it is flying. It takes just 3 to 4 shots with an assault rifle (and just one shot with a sniper rifle) and is a possible defense tactic if somebody else fires a LAW at you.
Also note that while the LAW is classified as a support weapon, it takes up a slot as a Primary Weapon instead. Therefore, if you buy the LAW, it should be backpacked.
The RPG-7 or Rocket Propelled Grenade is almost the same as a LAW. It is a higher rank than the LAW, but has slightly higher damage than the LAW. It works exactly like it's counterpart. Just point, aim, and shoot. If that person has taken ANY sort of damage, that RPG shot should kill him.