1940

Radar

Heinrich Hertz (1857–1894), Robert Watson-Watt (1892–1973), Arnold Frederic Wilkins (1907–1985), Edward George Bowen (1912–1991)

In World War I, airplanes were a recent invention, and a major threat. While soldiers could shoot down airplanes dropping bombs, they needed plenty of advanced warning, because airplanes are fast. The problem: there was no good way to sense airplanes from a distance. The best technology at the time used gigantic ear horns to hear airplanes as they approached. Today, these contraptions seem ridiculous, and they did not work particularly well. However, by World War II, the technological landscape had changed quite a bit.

The word “radar” stands for Radio Detection And Ranging. Research for what would become radar began as early as 1886, when German physicist Heinrich Hertz conclusively proved the existence of electromagnetic waves. However, it wasn’t until the Second World War that radar was used to detect airplanes at a distance using radio waves. The Chain Home system was deployed by Britain in 1940. The idea—developed by Robert Watson-Watt (descendent of James Watt, who invented the steam engine), Arnold Frederic Wilkins, and physicist Edward George Bowen—was to have a radar system that could look out from Britain and detect airplanes approximately 100 miles (160 km) away. The system was extremely important in the Battle of Britain, where Germany tried to use an aerial campaign to force a British surrender.

Radar is based on a simple idea: Send out a pulse of radio waves, then look for radio waves that get reflected back. By measuring the length of time taken for the reflection to return, a good estimate of distance is possible. An oscilloscope-like display showed blips of reflected energy on a screen. Interestingly, the Chain Home system contained the engineering philosophy known as incremental improvement. The first iteration was nowhere near perfect or ideal, but it was good enough to receive reflections and provide some sense of distance and direction. Improved systems were developed and installed over time. The power of the transmitters increased, giving better range. New systems detected airplanes closer to the ground. Rotating antennas and much better displays arrived.

Electrical engineers had developed a completely new sense for human beings. Today we still use radar for many applications, including self-driving cars.

SEE ALSO High-Pressure Steam Engine (1800), Cluster Munition (1965), F-117 Stealth Fighter (1983), Self-Driving Car (2011).

A Japanese sound detector, made obsolete by the discovery of radar.