From surplus equipment to public service
When the Second World War ended in 1945, armed forces on both sides of the Atlantic had thousands of radar sets and a large pool of trained technicians. The war’s radar had been developed for air defense, ship detection and gunnery. Afterward, the same equipment and people were available for peacetime tasks, and the postwar growth of air travel, shipping and weather services gave radar new reasons to exist. This article focuses on three areas where civilian radar made the biggest difference. The wartime research itself is only summarized here: the basic principle is a pulse of radio energy sent out, with the returning echo timed to calculate distance.
Air traffic control
Before radar, air traffic controllers relied on pilots’ position reports by radio and on procedures that kept aircraft apart by time and altitude. This worked when there were few flights, but it became strained as traffic grew after the war. Radar let controllers see aircraft on a screen, not just estimate where they were.
One of the first wartime systems used for civilian aviation was Ground Controlled Approach, a radar-guided method in which a controller talked pilots down to a runway in poor visibility. In the late 1940s and 1950s, airports and en route centers began installing surveillance radar. Over time, a second system was added: secondary radar, in which an aircraft carries a transponder that replies to a ground signal with an identity code and altitude. The idea grew out of wartime “identification friend or foe” equipment. Together, these tools made air traffic control a radar-based service in much of the world by the 1960s, and later computers added automatic tracking and conflict alerts. Radar did not eliminate accidents or delays, and controllers still work with procedures and communication, but it increased the number of aircraft that could be handled safely.
Weather observation
Operators of wartime radar noticed that rain, storm cells and clouds produced echoes that cluttered their screens. Meteorologists realized the same echoes could reveal where precipitation was falling and how heavy it was. In the late 1940s and 1950s, surplus military sets were adapted for weather observation, and national weather services began building networks of dedicated radars.
The resulting weather radar could track storms, hurricanes and squall lines over areas that ground observers could not cover. Doppler radar, which measures the motion of precipitation toward or away from the radar as well as its position, improved the detection of rotation in storms. In the United States, a national Doppler network was deployed in the 1990s, and similar systems operate in many countries today. Radar images became a regular feature of television forecasts and, later, online maps. Satellites, including weather satellites, complement radar by providing a broader view, and the two are used together for short-term forecasting. Radar-based warnings can help people take shelter, though forecasts and warnings are never perfectly accurate.
Ship navigation
At sea, radar addressed an old problem: seeing other vessels, coastlines and hazards in fog and darkness. Commercial marine radar sets appeared in the late 1940s, and they spread across merchant fleets and large yachts through the 1950s. Radar allowed a bridge officer to see the position of other ships and judge their courses, and it made harbor approaches in poor weather more manageable.
It also introduced new risks. Some collisions in the 1950s were blamed partly on misuse of radar, such as assuming the picture showed more than it did or maintaining high speeds in fog. Rules of the road at sea were revised to account for radar, and training became a requirement. Over the decades, marine radar added features such as automatic plotting of other vessels’ tracks. Today, ships combine radar with satellite navigation, electronic charts and automatic identification systems.
Other everyday uses
Radar spread into other areas as well. Police radar guns, which use the Doppler effect to measure vehicle speed, appeared in the late 1940s and 1950s. Airport ground radar helps track aircraft and vehicles on the surface. Scientists use radar for mapping terrain from aircraft and satellites, studying the upper atmosphere and observing the Moon and planets. Radio astronomers borrowed wartime receivers and antennas for their own research.
A related wartime component, the cavity magnetron, helped lead to a very different domestic product, since microwave ovens grew from engineers’ experience with that technology after the war. The story is often told with Percy Spencer of Raytheon, though such origin tales are usually simplified.
Lasting effects
Radar is a good example of defense research that found wider uses. Its civilian history shows a pattern: the technology was adapted to solve problems that grew as society changed, in this case more flights, busier shipping lanes and a greater demand for reliable weather information. Today’s systems use solid-state electronics and digital processing rather than vacuum tubes and analog screens, but the basic echo-timing principle remains unchanged.