A very common and very powerful big gun, the potential of the missile launcher is somewhat reduced by its long reload time and inability to kill anything stronger than a super mutant brute in a single shot.
Missile launchers can be wielded by a wide variety of both enemies and friendlies. When encountered in squads, super mutants, raiders, and Talon company mercs usually have at least one character wielding a heavy weapon, which can be a missile launcher.
One can be obtained from the VSS armory after completing Operation: Anchorage.
Raiders rarely carry them, but when they do, they are usually in poor condition.
Super mutants often carry them when in big groups.
One can be found around the back of the Washington Monument, along with an ammunition box full of missiles.
The missile launcher will "lock-on" on certain metallic objects, most notably turrets and the heads of many robot types, giving an increased chance to hit even at long range. This homing ability is perhaps why it is a missile launcher as opposed to a simpler unguided rocket launcher. (If used in V.A.T.S. (with sufficient skill) against a fast moving target, the missile quite obviously curves and tracks the targeted body part.)
A special missile launcher with no name, appearing as <Missing Name> in the inventory, can be obtained on Windows using the console command player.additem 0005deee 1. This weapon is used by the SatCom nuclear strike and is what creates the rain of Satcom missiles that are called upon from the Satcom array. It fires missiles, however the explosion is much larger than that of the mini nuke, and gives +40 Rads/sec at the impact zone.