The US Army TACOM group is spending $2.25 million on research projects aimed at building robot dogs that can carry a soldier's field equipment and keep up with the soldier over any terrain. Right now, each man has to carry up to 100 pounds of ammunition, food, and equipment. The long term challenge is making a four legged robot that can move as fast and quietly as a man over any terrain. The immediate challenge is making a four legged robot big enough for the job that doesn't fall over and doesn't need an internal combustion engine for power. For more, see Noah Shachtman's interesting article on the program in Wired.