Guided Missile is a short mission in which you play as a guided missile (a locked captain with jetpack and hover device) which destroys enemy aircraft by flying into them. There are three aircraft to destroy, one spaceship that you reach using a missile launcher stuck into a mountain, and three aircraft that you destroy by hitting an energy generator that they are guarding. Then it's a thirty-second race through flames and an easy-to-avoid mine field to an allied ship before the blast kills you.
In total, the mission takes a little more than a minute.
(I have a feeling I may have put more people off playing it than I encouraged to play it with that description...)
Note that there are a couple of glitches if you don't control the missile properly at a couple of points, which can result in you being left helpless and at the mercy of your enemies. Nothing too major, though.