Military Robot 2013 DARPA LS3 Automatically Follows Soldiers
Contunually blowing our minds DARPA is probably the most advanced technology group on the planet.

It's absolutely amazing, just masterful. But I do wonder why you couldn't just use a horse. It doesn't look like it would do any better against bullets and certainly isn't faster or quieter. That being said, the technology they've had to develop will certainly be invaluable in other area's. It just doesn't seem extremely practical, for the moment that is.