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MIT Radiation Laboratory

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MIT Radiation Laboratory

The Radiation Laboratory, commonly called the Rad Lab, was a microwave and radar research laboratory located at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts. It was first created in October 1940 and operated until 31 December 1945 when its functions were dispersed to industry, other departments within MIT, and in 1951, the newly formed MIT Lincoln Laboratory.

The use of microwaves for various radio and radar uses was highly desired before the war, but existing microwave devices like the klystron were far too low powered to be useful. Alfred Lee Loomis, a millionaire and physicist who headed his own private laboratory, organized the Microwave Committee to consider these devices and look for improvements. In early 1940, Winston Churchill organized what became the Tizard Mission to introduce U.S. researchers to several new technologies the UK had been developing.

Among these was the cavity magnetron, a leap forward in the creation of microwaves that made them practical for use in aircraft for the first time. GEC made 12 prototype cavity magnetrons at Wembley in August 1940, and No 12 was sent to America with Bowen via the Tizard Mission, where it was shown on 19 September 1940 in Alfred Loomis’ apartment. The American NDRC Microwave Committee was stunned at the power level produced. However Bell Labs director Mervin Kelly was upset when it was X-rayed and had eight holes rather than the six holes shown on the GEC plans. After contacting (via the transatlantic cable) Dr Eric Megaw, GEC’s vacuum tube expert, Megaw recalled that when he had asked for 12 prototypes he said make 10 with 6 holes, one with 7 and one with 8; and there was no time to amend the drawings. No 12 with 8 holes was chosen for the Tizard Mission. So Bell Labs chose to copy the sample; and while early British magnetrons had six cavities American ones had eight cavities.

Loomis arranged for funding under the National Defense Research Committee (NDRC) and reorganized the Microwave Committee at MIT to study the magnetron and radar technology in general. Lee A. DuBridge served as the Rad Lab director. The lab rapidly expanded, and within months was larger than the UK's efforts which had been running for several years by this point. By 1943 the lab began to deliver a stream of ever-improved devices, which could be produced in huge numbers by the U.S.'s industrial base. At its peak, the Rad Lab employed 4,000 at MIT and several other labs around the world, and designed half of all the radar systems used during the war.

By the end of the war, the U.S. held a leadership position in a number of microwave-related fields. Among their notable products were the SCR-584, the finest gun-laying radar of the war, and the SCR-720, an aircraft interception radar that became the standard late-war system for both U.S. and UK night fighters. They also developed the H2X, a version of the British H2S bombing radar that operated at shorter wavelengths in the X band. The Rad Lab also developed Loran-A, the first worldwide radio navigation system, which originally was known as "LRN" for Loomis Radio Navigation.

During the mid- and late-1930s, radio systems for the detection and location of distant targets had been developed under great secrecy in the United States and Great Britain, as well as in several other nations, notably Germany, the USSR, and Japan. These usually operated at Very High Frequency (VHF) wavelengths in the electromagnetic spectrum and carried several cover names, such as Ranging and Direction Finding (RDF) in Great Britain. In 1941, the U.S. Navy coined the acronym 'RADAR' (RAdio Detection And Ranging) for such systems; this soon led to the name 'radar' and spread to other countries.

The potential advantages of operating such systems in the Ultra High Frequency (UHF or microwave) region were well known and vigorously pursued. One of these advantages was smaller antennas, a critical need for detection systems on aircraft. The primary technical barrier to developing UHF systems was the lack of a usable source for generating high-power microwaves. In February 1940, researchers John Randall and Harry Boot at Birmingham University in Great Britain built a resonant cavity magnetron to fill this need; it was quickly placed within the highest level of secrecy.

Shortly after this breakthrough, Britain's Prime Minister Winston Churchill and President Roosevelt agreed that the two nations would pool their technical secrets and jointly develop many urgently needed warfare technologies. At the initiation of this exchange in the late summer of 1940, the Tizard Mission brought to America one of the first of the new magnetrons. On October 6, Edward George Bowen, a key developer of RDF at the Telecommunications Research Establishment (TRE) and a member of the mission, demonstrated the magnetron, producing some 15,000 watts (15 kW) of power at 3 GHz, i.e. a wavelength of 10 cm.

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