It's one of those great 20th century ironies that the most effective method ever invented to defeat radar had nothing to do with electronics. This is stealth technology, which is all about designing the shape of aircraft, and the materials it is made from, to minimize the effectiveness of radar. The basic concepts of stealth had been around since World War II, when it was noted that the British Mosquito light bomber, made largely of wood (except for the engines and a few other parts) was more difficult to pick up on radar. Soviet scientists later developed wavelength theory that American engineers used to develop the odd shaped F-117 stealth warplane. This aircraft was developed in great secrecy in the 1970s, as knowledge of it would enable the Soviets to develop ways to un-stealth it. Serbs shot down a F-117 in 1999 using a combination of spies (someone near the F-117 airbase may have radioed back when the stealth aircraft took off, thus warning the Serbs that one was on the way), radars that are better able to pick up the F-117 (some 1950s era radars can do this) and knowledge that when the F-117 opens its bomb bay, those open doors briefly make the aircraft more visible to regular radar. This combination enabled the Serbs to nail a F-117. Several nations now offer radars that claim they can spot an F-117. But nothing stands still in electronic warfare. The B-2 stealth bomber, developed in the 1980s, uses second generation stealth technology. What can spot a F-117, won't work very well against the B-2. And then there's the F-22 and JSF, using third generation stealth technology developed in the 1990s. The only problem with stealth bombers is that American commanders are no longer willing to risk losing aircraft or pilots. Stealth aircraft are also much more expensive (the B-2 cost over a billion each and the F-22 over a hundred million each), meaning commanders are reluctant to risk losing them. This reluctance hampers a commanders flexibility. Sometimes the best thing to do is charge right in, take the risks, but end the battle sooner and save a lot more lives. In any event, there are a lot fewer of these pricey aircraft (40 F-117s, 20 B-2s, a few hundred F-22s eventually, perhaps more JSF, or none at all if JSF is cancelled.) Another problem is that it is theoretically possible for new technologies to strip away stealth's invisibility. This makes stealth aircraft a rather brittle weapon. Very deadly when used, but likely to lose most of their advantage quickly if the right new radar comes along. But until that time, stealth bombers make it impossible for a foe to protect any target, no matter how many anti-aircraft weapons are used. This was to major breakthrough, for before that, if you wanted to protect something badly enough, you could. Now the only protection left is deception, particularly camouflage and related tricks. But if a stealth armed adversary knows where you are, you're toast.