Army's have always taken more casualties than air forces or navy's. So why hasn't the ground combat crowd acquired robots for their more dangerous work? Because land warfare is a lot more complicated and messy that in the air or at sea. The most dangerous infantry work is sneaking around forests or buildings, never knowing exactly where the enemy is or when a firefight will break out. By far the most dangerous job is "point"; the guy who goes ahead to prevent ambushes. Often he just gets shot. Even when defending, there has to be some troops out front to provide some warning of an attack. Dangerous business. Perfect for robots.
The US Marines are buying two models of robots for fighting in urban areas, a type of combat more dangerous than out in the countryside. The K8 weighs 30 pounds (so it can be carried to buildings where it is needed) and small (24x20x7 inches). It carries video, infrared and still cameras, as well as microphones. It broadcasts what it sees and hears to nearby troops. Using tracked paddles to get around, the K8 can climb stairs and rubble. If it gets knocked over, it's paddles can right it. It's also built to survive a six foot drop, for often the troops will have to throw the K8 through a window or a door so the K8 can check out a potentially dangerous situation. This feature will save a lot of civilian lives, for previously the only thing you could do was throw a grenade into questionable locations.
The other marine robot is the Lemming. Roughly the same size as the K8, it has an arm that can carry a camera so a picture can be obtained without exposing the entire robot to possible enemy fire (like looking around a corner.) The Lemming can also operate under water, making it perfect for checking out sewers (the Lemming also cannot smell, eliminating another distraction when scouting out sewers.)
The army looked into mobile (like the K8) anti-tank robots in the 1980s, but never went past the discussion stage. Then, as now, it was noted that cheap (relatively) civilian technology was increasingly suitable for things like combat robots. And the technology was getting better, and cheaper, every year. The Israelis had long been taking advantage of this approach to develop successful robotic recon aircraft, while the US armed forces stumbled along doing it the old fashioned way (sort of reinventing the wheel, rather than buying a better and cheaper one at Wal-Mart.) The 1970s US cruise missile boasted extensive use of off the shelf technology. There was a trend, using newer and cheaper instead of milspec (military specification, meaning too expensive, obsolete or both).
Looking at what technology was now available, there developed the idea of making combat druids that were "fast, cheap and out of control." Not fast speedwise, but more in terms of thought, artificial thought. Cheap in terms of making many thousands of the robots. Out of control in that you just turned them loose much of the time. All three of these approaches had already crept into various weapons over the last few decades. Faster microcomputer technology had made missiles, radars and navigation equipment smarter, and faster to do what they did. Electronics became so cheap that tanks now have dozens of microprocessors, and individual soldiers carry a few around in GPS or radio sets. "Out of control" is more commonly known as "fire and forget." All this is coming together in the design of infantry robots. The battle droids have to think fast to find their way around the battlefield. During the first attempts at driving a truck (or tank) using a computer, it was obvious you needed a very powerful microprocessor to deal with all the decisions we take for granted when roaring down the highway or cross country. But there is sufficient cheap computing power for a slow moving robot, under some degree of human control, to be made cheap and light. Inexpensive digital video, battery, miniature electric motors and wireless technology that provide cheap cameras, toys and cell phones also combine to make combat robots.
Finally, robots have joined the infantry. Robots have been serving in the armed forces for over a century. In the 19th century there was the torpedo, the robotic equivalent of the ancient fire ship (which was loaded with combustible material and aimed by it's skeleton crew at larger enemy ships and set afire before impact.) The torpedo moved at high speed just below the surface, making it harder to spot, and avoid. Modern torpedoes are "fire and forget," as they can go looking for targets on their own. Then came naval and land mines, some now equipped with computers, sensors and some mobility. The air force has had cruise missiles for several decades, and the navy has missiles that seek out enemy ships and attack them. The air force has used robot reconnaissance aircraft since the 1970s, and now has models that can cross oceans and stay aloft longer than any manned aircraft. Robot bombers and fighters are being designed. Everyone has gotten into the robotic warrior business except the army, until now.