The ground-based military arm of the Terran Federation, as told by Robert Heinlein's science fiction novel Starship Troopers.
What makes the Mobile Infantry unique in all of science fiction literature is the complex suit, or battle armor, that each infantryman wears. Heinlein was the first to visualize such a device, and since then it has been borrowed and repeated in many forms.
The suit adds protection against any type of small arms fire and some protection against concussive blasts. Its armaments include nuclear rockets, small bomblets that can be "tossed" in any direction from racks on the back of the suit, and a hand-flamer (for close encounters).
M.I. units deploy from Fleet ships in orbit around the target planet. A pod encases the suit and the infantryman, protecting him as he enters the planet's atmosphere. The ablative shield burns off on entry, and air brakes extend to slow the pod even more. At high altitude the trooper will abandon his pod and ride down in his suit. The components of the pod serve to confuse enemy ground radar and AAA guns.
Once on the ground, the speed and jump jets of the suit allow a single man to cover many square miles of the battlefield.