In the late 1990s, there was a major break through in bombing accuracy, that is about to be undone by electronic warfare. The JDAM (Joint Direct Attack Munition) came into use. Not a weapon itself, the JDAM is a kit that is screwed on to 1,000 or 2,000 pound bombs. Using GPS signals and an INS (Inertial Guidance System) to locate itself and its target, and an onboard computer, battery and electric motors to move flaps, the JDAM equipped bomb can glide up to 24 kilometers to its target and land within ten meters of its target. The JDAM equipped bombs have worked 95 percent of the time and half landed within ten meters of the target (most of the rest landed only a few meters farther away, not much of a miss for bombs that big.) The JDAM has two advantages over earlier laser guided bombs. First, the JDAM does not need a laser signal bounced off the target. Laser cannot operate through mist and smoke. Secondly, not needing a sensor to spot the reflected laser light brings the cost of JDAM way down. The average JDAM kit costs some $21,000, compared to over $100,000 for laser guided bombing kits. Now the bad news. GPS signals can be jammed. Jammers are easy to make and the Russians, among others, sell a "military grade" jammer. Protecting against jamming is expensive, difficult and unpredictable. JDAM is designed to go with the INS alone if the GPS fails or is jammed, but this reduces accuracy considerably. Like most forms of electronic warfare, you never know who has the best approach to protecting, or disrupting, GPS until there's a situation where someone tries to jam JDAM. No one is sure who will come out ahead.