In 2001, the Pentagon had just 200 robotic aircraft. In 2008 it had more than 5,000. The number of military ground robots jumped from 160 in 2004 to around 4,000 in 2006. Only underwater robots lagged: so far just a few dozen systems have entered service. Under the water is, after all, the toughest environment for robots. But even undersea bots will see a boost in coming years. The Pentagon has plans to spend at least $4 billion a year for the foreseeable future designing and building robots.

The spread of robots in our armies, navies and air forces has greatly advanced the science, engineering and techniques for mixing thinking people and thinking machines. And it has forced us to try answering a basic moral question. Just how much responsibility should we surrender to machines? If and when robots fulfill their promise to make war cheaper and easier for our side, will we discover that we wage war too lightly? Are we already guilty of that sin?

This book examines just a handful of the many types of war bots, and just a few of the ways they're being used in the expanding American-led "war on terror." Some of these robots have been in service for years. Some are still just prototypes. Between them they span the entire range of military robotics. Some are killers. Others are helpers. All of them are soldiers with no fear.