Watson-Watt , Sir Robert Alexander

(1892–1973) British physicist

Watson-Watt was born Robert Watt at Brechin in Scotland. The Watson part of his name came from his mother's family and the hybrid Watson-Watt was adopted in 1942 on receipt of his knighthood. He was the son of a carpenter and was educated at the University of St. Andrews. After graduating in 1912 he immediately joined the faculty but found his academic career disrupted by World War I. He spent much of the war working as a meteorologist at the Royal Aircraft Establishment, Farnborough, attempting to locate thunderstorms with radio waves.

He remained in the scientific civil service after the war and in 1921 was appointed superintendent of the Radio Research Station at Slough. In 1935 he was asked by the Air Ministry if a ‘death ray’ could be built – one capable of eliminating an approaching enemy pilot. Watson-Watt asked a colleague to calculate how much energy would be needed to raise a gallon of water from 98°F to 105°F at a distance of a mile, i.e., a significant rise in body temperature. He advised the Ministry that the energy needed outstripped the available technology.

Watson-Watt also pointed out that Post Office engineers had noted interference in radio reception as aircraft flew close to their receivers. Interference of this kind, he suggested, could perhaps be used to detect the approach of enemy aircraft. In 1935 he submitted an important paper, The Detection of Aircraft by Radio Methods, to Tizard at the Ministry. Watson-Watt was normally a man, it was said, who could never say in one word what could be said in a thousand. This time, however, the report was terse and to the point. Tizard asked for a demonstration. In February 1935 the BBC short-wave transmitter at Daventry was successfully used to identify the approach of a Heyford bomber eight miles away.

Tizard moved quickly. Watson-Watt was invited to set up a research station at Bawdsley in Suffolk to develop radio detection and ranging; the acronym ‘radar’ was first recorded in use in the New York Times in 1941.

The principles behind radar are relatively simple. Radio waves are reflected strongly off large objects such as airplanes. The difficulty was that very little, something of the order of 10^–12, of the transmitted signal would be picked up by the receiving antennae. Both high transmitting power and high amplification would therefore be needed. Watson-Watt assembled a talented team at Bawdsley and by the outbreak of World War II an operational chain of eight stations, known as ‘Chain Home’, defended Britain's eastern and southern coasts. They operated in the high-frequency bands and required very visible 360-foot-high transmitters and 240-foot-high receivers.

Watson-Watt left Bawdsley in 1938 for the Air Ministry and the post of director of communication development. His main task was to make radar workable, to ensure that it was acceptable to the RAF and that they could actually operate the new equipment. He also had to arrange for the manufacture of the relevant transmitters, receivers, and electron tubes.

He finally left the civil service in 1945 to set up as a consultant. He was also invited to give evidence before the Royal Commission on Inventors on behalf of his colleagues and himself. After speaking for six days Watson-Watt was awarded £52,000 for his work on radar.