By the late nineteen thirties, several countries were secretly experimenting with this idea. Britain, Germany, the United States, the Soviet Union, and Japan all had research efforts in motion. But Britain took an early and especially organized lead. In nineteen thirty five, a scientist named Robert Watson Watt proposed that radio waves could detect aircraft at long range. In a famous early test, a bomber flew along a radio transmission path and technicians saw its effect on the signal. That crude experiment convinced British leaders to invest heavily.Britain then built a chain of tall antenna stations along its eastern and southern coasts. This system was called Chain Home. Each station sent out radio pulses and listened for echoes from incoming aircraft. The range was impressive for the time, often more than one hundred miles. The resolution was poor and the equipment was bulky, but the system did not need to be perfect. It just needed to tell the Royal Air Force that enemy aircraft were coming and roughly where.When Germany began its air assault on Britain in nineteen forty, those stations went to work. Radar gave British commanders something they had never had before, early and fairly reliable warning. Instead of sending fighter planes to patrol aimlessly and burn fuel waiting for the enemy, they could keep them on the ground until Chain Home showed a raid forming. Then they could scramble exactly the number of fighters needed and direct them to the right area.This early warning system turned what might have been a chaotic defense into a coordinated one. German crews did not understand at first why British fighters appeared so often in the right place at the right time. To them it seemed like uncanny luck. In reality, women and men in radar huts and operations rooms, using wall maps and colored markers, were tracking raids in nearly real time. Radar did not win the Battle of Britain alone, but it was a critical part of that victory.While Britain focused on long range air defense, scientists in several countries raced to improve the core technology. They wanted shorter wavelengths, higher power, and smaller sets. Shorter wavelengths allowed smaller antennas and finer detail. The breakthrough came with the cavity magnetron, a compact device that generated very powerful microwaves. British researchers developed a practical magnetron early in the war.In nineteen forty, Britain shared this precious secret with the United States in what is often called the Tizard Mission. A small group of British scientists carried a black box full of advanced technology across the Atlantic, including the magnetron. American industrial capacity then did something Britain alone could not. Laboratories like the Radiation Laboratory at the Massachusetts Institute of Technology turned these ideas into thousands of reliable radar sets adapted for ships, aircraft, and ground use.At sea, radar changed the nature of naval warfare. Before radar, fighting at night or in fog was nerve wracking guesswork. Ships could collide with enemies or even with each other. After radar, a destroyer could see an approaching surface contact in darkness and open fire before the other side knew it had been detected. The United States Navy and the Royal Navy fitted many of their vessels with surface search radar and fire control radar that helped aim guns.German U boats had been terrors of the Atlantic early in the war. They hunted at night on the surface, recharging batteries and using their low silhouette to remain unseen. Once Allied aircraft gained airborne radar, that advantage shrank. Patrol planes could now pick up even a small submarine on the surface at night or in bad weather. As radar improved, U boats were forced to spend more time underwater, where they were slower and less effective.In the air, radar took several forms. Ground based radar guided fighters to intercept bombers. Airborne interception radar sets were mounted inside night fighters. These allowed a pilot and a radar operator to stalk enemy bombers in the dark, homing in on the radar echo. German and British night fighters used these systems to deadly effect.Another dramatic use was ground mapping radar in bombers. Flying over enemy territory at night or through cloud, crews could use radar images of coastlines, rivers, and cities to find their targets. American bombers in the Pacific used radar to hit ships and island positions even when they could not see them. In Europe, British pathfinder crews used radar aids to drop marker flares over industrial areas.As radar spread, a new kind of hidden war began, the battle of radar and countermeasures. Once the Germans realized that British bombers were using a particular radar aid, they tried to jam or deceive it. Allied scientists answered with changes in frequency, more powerful signals, and clever tricks. One famous trick was called chaff. Crews dropped bundles of thin metal strips from aircraft. These strips reflected radar strongly, creating clouds of false echoes on enemy screens and confusing their defenses.On the German side, radar was also central. They built their own air defense network with early warning stations that could detect Allied bombers crossing the coast. Large dishes scanned the skies, feeding information to controllers who vectored night fighters into position. German ships and U boats received their own radar sets, though in smaller numbers than the Allies. Late in the war, sets tuned to microwave frequencies finally reached German forces, but by then it was too late to change the outcome.In the Pacific, radar had a different but equally important role. The vast distances and sudden weather changes made early detection vital. American fleets used radar to spot incoming Japanese aircraft long before lookouts could see them. This warning allowed combat air patrol fighters to climb into position and also gave ship crews time to man antiaircraft guns. During terrifying kamikaze attacks, radar guided guns and directed fighters, reducing but not eliminating the damage those desperate strikes inflicted.
