Fired from ships or planes, the missiles fly at a low altitude, navigating via an onboard computer that reads their position against pre-loaded contour maps of the ground below, adjusted by information from a global positioning satellite system. So what causes them to miss? "Anything from a fuel-flow problem to computer problems to fins bent by the tough G-forces on takeoff," says Thompson. The Navy believes its Tomahawk cruise missiles are now accurate to within 15 yards of their target, 85 percent of the time. As a sign of that confidence, Thompson notes, "where they used to aim three missiles at the same target to account for error, they now aim only two."
Cruise missiles are pretty smart, but they do make mistakes. Pakistan claimed Monday to have found one near its western border following last week's U.S. strike on Afghanistan. If confirmed, the find would underline the "could do better" side of the missile's report card. "Cruise missiles are educable rather than smart," says TIME Pentagon correspondent Mark Thompson. "During the U.S. strike on Baghdad in 1993, 16 out of 24 hit their targets."