The British government was spooked back in 1935. Not because of Hitler’s air force or his infantry. Because of his death ray.
Newspapers screamed that the Nazis might have a super-weapon that could incinerate living tissue or detonate a bomb at long distance. Flooded by letters begging for a response, the British Air Ministry asked prominent physicist Robert Watson-Watt to see if a radio-wave-based death ray was feasible.
Within ten days Watson-Watt reported that such a weapon was unlikely. But using radio waves to locate an approaching bomber was a real possibility. And that's how radar was born.
Robert Watson-Watt is given the credit for inventing the radar. In fact, this credit should go to the German engineer Christian Hulsmeyer who in 1904, using patented an early warning system for shipping. He, in turn, used a discovery by Heinrich Hertz who had discovered in 1888 that radio waves could be bounced off objects.
In 1935, Robert Watson-Watt - a Scottish physicist - was asked by the Air Ministry to investigate the possibility of creating a "death-ray" weapon using radio waves. Watson-Watt was working at the National Physical Laboratory in Slough.
Watson-Watt did not create a "death-ray" weapon but he did find that his radio transmitters could create an echo from an aeroplane that was over 200 miles away. This information would give the Royal Air Force an early warning of an attack by enemy fighters. By the time an enemy force was nearing the coastline, fighters would be airborne and ready to fight. The enemy would have lost the element of surprise. This invention by Watson-Watt was vital to the RAF during the Battle of Britain in 1940.
In 1940, aided by John Randall and Henry Boot from Birmingham University, Robert Watson-Watt invented the cavity magnetron. This produced a compact source of short-wave radio waves and allowed Fighter Command of the RAF to detect incoming enemy planes from a much greater distance thus giving the pilots more time to organize themselves.
In August 1917 Nikola Tesla outlined a concept for primitive radar-like units. He stated:
"...by their [standing electromagnetic short waves] use we may produce at will, from a sending station, an electrical effect in any particular region of the globe; [with which] we may determine the relative position or course of a moving object, such as a vessel at sea, the distance traversed by the same, or its speed".
Everyone has heard of RADAR, but few people know that the men who built the first primitive RADAR units in 1934 were following principals, mainly regarding frequency and power level, that were first established by Tesla in 1917.
Tesla’s 1917 proposal for Directed Energy submarine warfare (Tesla's Views on Electricity and the War - The Electrical Experimenter - August, 1917 and New Yankee Tricks to Circumvent the U-Boat - The Fort Wayne Journal-Gazette, Fort Wayne, Indiana - August 19, 1917) is eerily similar to a 2008 US Department of Defense proposal:
“I believe the magnetic method of locating or indicating the presence of an iron or steel mass might prove very practical in locating a hidden submarine. And it is of course of paramount importance that we do find a means of accurately locating the sub-sea fighters when they are submerged, so that we can, with this information, be ready to close in on them when they attempt to come to the surface. Especially is this important when several vessels are traveling in fleet formation; the location and presence of the enemy submarine can be radiographed to the other vessels by the one doing the magnetic surveying and, by means of nets in some cases, or gun-fire and the use of hydro-aeroplanes sent aloft from the ships, the enemy under water stands a mighty good chance of being either ‘bombed,’ shelled or netted.
“However, a means would soon be found of nullifying this magnetic detector of the submerged undersea war-craft. They might make the ‘U-boat’ hulls of some non-magnetic metal, such as copper, brass, or aluminum. It is a good rule to always keep in mind that for practically every good invention of such a kind as this, there has always been invented an opposite, and equally efficient counteracting invention.”
“Now suppose that we erect on a vessel a large rectangular helice or inductance coil of insulated wire. Actual experiments in my laboratory at Houston Street (New York City) have proven that the presence of a local iron mass such as the ship’s hull would not interfere with the action of this device. To this coil of wire, measuring perhaps 400 feet in length by 70 feet in width (the breadth of the ship), we connect a source of extremely high frequency and very powerful oscillating current. By this means there are radiated powerful oscillating electro-static currents, which as I have found by actual experiment in my Colorado tests some years ago, will first affect a metallic body (such as a submarine hull, even though made of brass or any other metal), and in turn cause that mass to react inductively on the exciting coil on the ship. To locate an iron mass, it is not necessary to excite the coil with a high frequency current; the critical balance of the coil will be affected simply by the presence of the magnetic body. To be able to accurately determine the direction and range of the enemy submarine, four exciting inductances should be used.** With a single inductance, however, it would be possible to determine the location of a submarine by running the ship first in one direction and then in another, and noting whether the reactance effect caused by the presence of the submarine hull increased or decreased. The radiating inductance must be very sharply attuned to the measuring apparatus installed on the ship, when no trouble will be found in detecting the presence of such a large metallic mass as a submarine, even at a distance of 5 to 6 miles; of this I feel confident from my past experiments in the realm of ultra-high frequency currents and potentials.”
Neither a single nation nor a single person can say that the discovery and development of radar technology was his (or its) own invention. One must see the knowledge about “Radar” than an accumulation of many developments and improvements, in which any scientists from several nations took part in parallel. In the past, there are nevertheless some milestones, with the discovery of important basic knowledge and important inventions:
"...by their [standing electromagnetic waves] use we may produce at will, from a sending station, an electrical effect in any particular region of the globe; [with which] we may determine the relative position or course of a moving object, such as a vessel at sea, the distance traversed by the same, or its speed"
Driven by general war events and the development of the Air Force to major branch of service, the radar technology undergoes a strong development boost during the World War II, and radar sets were used during the "Cold War" in large numbers along the inner German border.
There exist various aplications for the radar invention:
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