The cavity magnetron is a high-power vacuum tube used in early radar systems and subsequently in microwave ovens and in linear particle accelerators. A cavity magnetron generates microwaves using the interaction of a stream of electrons with a magnetic field, while moving past a series of cavity resonators, which are small, open cavities in a metal block. Electrons pass by the cavities and cause microwaves to oscillate within, similar to the functioning of a whistle producing a tone when excited by an air stream blown past its opening. The resonant frequency of the arrangement is determined by the cavities' physical dimensions. Unlike other vacuum tubes, such as a klystron or a traveling-wave tube (TWT), the magnetron cannot function as an amplifier for increasing the intensity of an applied microwave signal; the magnetron serves solely as an electronic oscillator generating a microwave signal from direct current electricity supplied to the vacuum tube.
The SCR-270 was one of the first operational early-warning radars. It was the U.S. Army's primary long-distance radar throughout World War II and was deployed around the world. It is also known as the Pearl Harbor Radar, since it was an SCR-270 set that detected the incoming raid about 45 minutes before the December 7, 1941, attack on Pearl Harbor commenced.
The Naxos radar warning receiver was a World War II German countermeasure to S band microwave radar produced by a cavity magnetron. Introduced in September 1943, it replaced Metox, which was incapable of detecting centimetric radar. Two versions were widely used, the FuG 350 Naxos Z that allowed night fighters to home in on H2S radars carried by RAF Bomber Command aircraft, and the FuMB 7 Naxos U for U-boats, offering early warning of the approach of RAF Coastal Command patrol aircraft equipped with ASV Mark III radar. A later model, Naxos ZR, provided warning of the approach of RAF night fighters equipped with AI Mk. VIII radar.
The history of radar started with experiments by Heinrich Hertz in the late 19th century that showed that radio waves were reflected by metallic objects. This possibility was suggested in James Clerk Maxwell's seminal work on electromagnetism. However, it was not until the early 20th century that systems able to use these principles were becoming widely available, and it was German inventor Christian Hülsmeyer who first used them to build a simple ship detection device intended to help avoid collisions in fog. True radar, such as the British Chain Home early warning system, which provided directional information about objects over short ranges, was developed over the next two decades.
The SCR-584 was an automatic-tracking microwave radar developed by the MIT Radiation Laboratory during World War II. It was one of the most advanced ground-based radars of its era, and became one of the primary gun laying radars used worldwide well into the 1950s. A trailer-mounted mobile version was the SCR-784.
An early-warning radar is any radar system used primarily for the long-range detection of its targets, i.e., allowing defences to be alerted as early as possible before the intruder reaches its target, giving the air defences the maximum time in which to operate. This contrasts with systems used primarily for tracking or gun laying, which tend to offer shorter ranges but offer much higher accuracy.
Signal Corps Radios were U.S. Army military communications components that comprised "sets". Under the Army Nomenclature System, the abbreviation SCR initially designated "Set, Complete Radio", but was later misinterpreted as "Signal Corps Radio."
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.
Signal Corps Laboratories (SCL) was formed on June 30, 1930, as part of the U.S. Army Signal Corps at Fort Monmouth, New Jersey. Through the years, the SCL had a number of changes in name, but remained the operation providing research and development services for the Signal Corps.
John William Marchetti was a radar pioneer who had an outstanding career combining government and industrial activities. He was born of immigrant parents in Boston, Massachusetts, and entered Columbia College and Columbia School of Engineering and Applied Science in 1925. In a six-year program combining liberal arts and engineering, he earned both A.B. and B.S. degrees, followed by the graduate E.E. degree in 1931. He was employed by New York Edison as a power engineer for several years, during which time he also participated in the U.S. Naval Reserve as an Ensign.
Radar in World War II greatly influenced many important aspects of the conflict. This revolutionary new technology of radio-based detection and tracking was used by both the Allies and Axis powers in World War II, which had evolved independently in a number of nations during the mid 1930s. At the outbreak of war in September 1939, both the United Kingdom and Germany had functioning radar systems. In the UK, it was called RDF, Range and Direction Finding, while in Germany the name Funkmeß (radio-measuring) was used, with apparatuses called Funkmessgerät . By the time of the Battle of Britain in mid-1940, the Royal Air Force (RAF) had fully integrated RDF as part of the national air defence.
Radar, Gun Laying, Mark III, or GL Mk. III for short, was a radar system used by the British Army to directly guide, or lay, anti-aircraft artillery (AA). The GL Mk. III was not a single radar, but a family of related designs that saw constant improvement during and after World War II. These were renamed shortly after their introduction in late 1942, becoming the Radar, AA, No. 3, and often paired with an early warning radar, the AA No. 4, which was also produced in several models.
The AN/APQ-7, or Eagle, was a radar bombsight system developed by the US Army Air Force. Early studies started in late 1941 under the direction of Luis Alvarez at the MIT Radiation Laboratory, but full-scale development did not begin until April 1943. By this time US-built, higher frequency systems promising better performance over the existing British H2S radar were entering production. Eagle's even higher resolution was considered important to Air Force planners who preferred precision bombing but were failing to deliver it, and high hopes were put on the system's abilities to directly attack small targets like docks and bridges.
Searchlight Control, SLC for short but nicknamed "Elsie", was a British Army VHF-band radar system that provided aiming guidance to an attached searchlight. By combining a searchlight with a radar, the radar did not have to be particularly accurate, it only had to be good enough to get the searchlight beam on the target. Once the target was lit, normal optical instruments could be used to guide the associated anti-aircraft artillery. This allowed the radar to be much smaller, simpler and less expensive than a system with enough accuracy to directly aim the guns, like the large and complex GL Mk. II radar. In 1943 the system was officially designated Radar, AA, No. 2, although this name is rarely used.
Radar, Anti-Aircraft, or simply AA radar for short, was a classification system for British Army radars introduced in 1943 and used into the 1960s when these systems were replaced by missiles with their own integral radar systems. The classification included subcategories, Number 1 through 8, as well as the many individual systems which were assigned Marks.
Radar, Air to Surface Vessel, or ASV radar for short, is a classification used by the Royal Air Force (RAF) to refer to a series of aircraft-mounted radar systems used to scan the surface of the ocean to locate ships and surfaced submarines. The first examples were developed just before the opening of World War II and they have remained a major instrument on patrol aircraft since that time. It is part of the wider surface-search radar classification, which includes similar radars in ground and ship mountings. And it constrasts with aircraft interception (AI) radar, which is used to detect flying aircraft rather than sea-suface vessels.
The M9 gun director was an electronic director developed by Bell Labs during World War II. This computer continuously calculated trigonometric firing solutions for anti-aircraft weapons against enemy aircraft. When cued by the SCR-584 centimetric gun-laying radar and used in concert with anti-aircraft guns firing shells with proximity fuzes, it helped form the most effective anti-aircraft weapon system utilized by the Allies during the war.
The SCR-720 was a World War II aircraft interception radar designed by the Radiation Laboratory (RadLab) at MIT in the United States. It was used by US Army Air Force night fighters as well as the Royal Air Force (RAF) in a slightly modified version known as Radar, Aircraft Interception, Mark X, or AI Mk. X for short.
AMES Type 6, also known as the Light Warning Set or L/W, was a portable early warning radar developed by the Air Ministry Experimental Station (AMES) for use by the Royal Air Force (RAF) in the field. Units in British Army service were officially known as Radar, Anti-Aircraft, Number 4, or AA. No. 4 for short, although this name was rarely used in practice. The system was also built in Canada for use by the US Army, which were known as SCR-602-A.
