They may be homemade, but improvised explosive devices used in attacks on U.S. and allied troops in Afghanistan are 50 percent more lethal than they were three years ago. According to Lt. Gen. Michael Oates, who spoke to a House subcommittee about IEDs, part of the reason is that insurgents are becoming more sophisticated. In the past year alone, the number of IED attacks has doubled over the past year. What makes them so treacherous is that they are often fertilizer-based and cannot be picked up by metal detectors. The military has not yet found a clear solution for dealing with them. "There is no silver bullet," Oates said.