SCR-584 radar
Encyclopedia
The SCR-584 was a microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...

 radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

 developed by the MIT Radiation Laboratory during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. It replaced the earlier and much more complex SCR-268 as the US Army's primary anti-aircraft gun laying
Gun laying
Gun laying is the process of aiming an artillery piece, such as a gun, howitzer or mortar on land or at sea against surface or air targets. It may be laying for direct fire, where the gun is aimed similarly to a rifle, or indirect fire, where firing data is calculated and applied to the sights...

 system as quickly as they could be produced. In service it proved to be an outstanding system, much more advanced than any other battlefield radar system deployed during the war.

Background

SCR-584 Technical Characteristics
Wavelength 10 cm
Frequency (four bands around 3,000 MHz)
Magnetron 2J32
Peak Power Output 250 kW
Pulse Width 0.8 microsecond
Pulse Repetition Frequency 1707 pulses per second
Antenna Diameter 6 feet
Beam width to half power 4 degrees
Maximum Range
   PPI Search 70,000 yards (39.7 statute miles)
   Auto-Track 32,000 yards (18.2 statute miles)
   Potentiometer Data (artillery control) 28,000 yards (15.9 statute miles)
Minimum Range 500 - 1000 yards
Lower Elevation Limit -175 mils
Angular mil
An angular mil, also mil, is a unit of angle. All versions of the angular mil are approximately the same size as a trigonometric milliradian.-History:The milliradian was first identified in the mid nineteenth Century...

 (-9.8 degrees)
Upper Elevation Limit +1,580 mils (+88.9 degrees)
Azimuth Coverage 360 degrees
Azimuthal scan rate in search mode 5 revolutions per minute
Range Error 25 yards
Azimuth Error 1 mil (0.06 degree)
Elevation Accuracy. 1 mil (0.06 degree)
Power Requirements 115 V, 60 Hz, 3 phase, 10 kVA maximum (without IFF)
The SCR-584 is built into a K-78 trailer. Its gross weight is 10 short ton
Short ton
The short ton is a unit of mass equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...

s. The overall length is 19.5 feet, width is 8 feet, height 10 feet, 4 inches

Data from U.S. War Department Technical Manuals TM11-1324 and TM11-1524
(published April, 1946 by the United States Government Printing Office
United States Government Printing Office
The United States Government Printing Office is an agency of the legislative branch of the United States federal government. The office prints documents produced by and for the federal government, including the Supreme Court, the Congress, the Executive Office of the President, executive...

)

The genesis of the SCR-584 started with the Tizard Mission
Tizard Mission
The Tizard Mission officially the British Technical and Scientific Mission was a British delegation that visited the United States during the Second World War in order to obtain the industrial resources to exploit the military potential of the research and development work completed by the UK up...

 in September 1940, when a group of British scientists travelled to the US to present various advances useful to the war effort. The British were initially hesitant to give away too much information without getting anything in return, however they learnt the US was in the process of developing two systems similar to their own existing Chain Home
Chain Home
Chain Home was the codename for the ring of coastal Early Warning radar stations built by the British before and during the Second World War. The system otherwise known as AMES Type 1 consisted of radar fixed on top of a radio tower mast, called a 'station' to provide long-range detection of...

 system, the Navy's CXAM
CXAM radar
The CXAM radar system was the first production radar system deployed on United States Navy ships. It followed several earlier prototype systems, such as the NRL radar installed in April 1937 on the destroyer ; its successor, the XAF, installed in December 1938 on the battleship ; and the first...

 and the Army's SCR-270. Neither of these systems had the accuracy needed to directly lay their associated guns, however. The US delegates then mentioned the Navy's work on a 10 cm wavelength radar, which would have the required resolution, but their klystron
Klystron
A klystron is a specialized linear-beam vacuum tube . Klystrons are used as amplifiers at microwave and radio frequencies to produce both low-power reference signals for superheterodyne radar receivers and to produce high-power carrier waves for communications and the driving force for modern...

 tube had very low power and was not practical.

Edward George Bowen
Edward George Bowen
Edward George 'Taffy' Bowen, CBE, FRS was a British physicist who made a major contribution to the development of radar, and so helped win both the Battle of Britain and the Battle of the Atlantic...

 had prepared for just this moment, and presented one of the earliest cavity magnetron
Cavity magnetron
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field. The 'resonant' cavity magnetron variant of the earlier magnetron tube was invented by John Randall and Harry Boot in 1940 at the University of...

s to the assembled researchers. It also worked at 10 cm, but offered even higher power than the US's existing longwave radars. One US historian later described it as the "most valuable cargo ever brought to our shores". The device was so much more advanced than anything in US use at the time that plans were immediately started to undertake a massive research and development program to quickly put it into production, leading to the creation of the Radiation Laboratory
Radiation Laboratory
The Radiation Laboratory, commonly called the Rad Lab, was located at the Massachusetts Institute of Technology in Cambridge, Massachusetts and functioned from October 1940 until December 31, 1945...

 (RadLab) and its many developments. The US would take over leadership in the radar field by the end of the war.

Development

Along with its SCR-270 early warning radar
Early warning radar
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 defences the maximum time in which to operate...

, the Army was also in the process of building an associated gun laying system, the SCR-268. Based on similar longwave technology, the SCR-268 was only marginally useful in its current form, with accuracy too low to directly lay the guns. While the SCR-268 had its operational problems, the real complaint was its size. Radio systems generally require antennas with lengths proportional to the wavelength being used, and thus inversely proportional to the frequency used. So in the case of the SCR-268's ~1.5 metre wavelength (205 MHz), the antenna was an extremely large system that presented serious logistics problems. A microwave radar in the 10 cm range could be aimed much more accurately while using a parabolic
Parabolic antenna
A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish...

 dish of much smaller size. For a given operating frequency, the larger the antenna's maximum dimension in a given direction, the narrower the radio beam angle along the normal to that dimension (at a right angle to the dimension in question), and thus the finer the bearing discrimination. At long ranges, range accuracy (which depends on time-interval discrimination) can achieve higher accuracy than bearing discrimination, for antennas of the typical dimensions discussed here.

A formal proposal for a SCR-268 replacement was made by the Signal Corps in January 1941, by which point the RadLab was already in the process of developing useful radar systems based on the magnetron. Instead of a simple system similar to the SCR-268 in concept, they instead proposed a much more advanced system which would directly aim the guns, a field MIT was particularly knowledgeable in due to work in the Servomechanisms Lab.

The RadLab had a prototype radar system running in April. The RadLab team, overseen by Lee Davenport
Lee Davenport
Lee L. Davenport was an American physicist. He was a member of the MIT Radiation Laboratory during World War II, responsible for the development and deployment of the SCR-584 radar system.-Early Life:...

To test the automatic aiming system, they attached the outputs from the radar to a gun turret taken from a B-29 bomber, removing the guns and replacing them with a camera. A friend then flew his light plane around the area, and on May 31 the system was able to accurately track the aircraft. Work then started on making the system suitable for field use, mounting the entire system in a single trailer with the 6-foot antenna on top. Known as XT-1, for eXperimental Truck-1, the system was first tested at Fort Monroe
Fort Monroe
Fort Monroe was a military installation in Hampton, Virginia—at Old Point Comfort, the southern tip of the Virginia Peninsula...

 in February 1942.
Work also started on a suitable gun-laying computer that could use electrical, as opposed to mechanical, inputs for pointing data. Bell Labs
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...

 delivered an analog computer
Analog computer
An analog computer is a form of computer that uses the continuously-changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved...

 known as the M-9 Director (military)
Director (military)
A director, also called an auxiliary predictor, is a mechanical or electronic computer that continuously calculates trigonometric firing solutions for use against a moving target, and transmits targeting data to direct the weapon firing crew....

 for this role, able to control four of the Army's standard 90 mm M3 guns. The entire system, including the M-9, was demonstrated in complete form on 1 April 1942. A contract for over 1,200 systems arrived the next day. Bell also worked on their own microwave radar as a backup project.

The SCR-584 was extremely advanced for its era. To achieve high accuracy it used a conical scanning
Conical scanning
Conical scanning is a system used in early radar units to improve their accuracy, as well as making it easier to steer the antenna properly to point at a target...

 system, in which the beam is rotated around the antenna's axis to find the maximum signal point, thus indicating which direction the antenna should move in order to point directly at the target. This system was not new, having been introduced on the German Würzburg radar
Würzburg radar
The Würzburg radar was the primary ground-based gun laying radar for both the Luftwaffe and the German Army during World War II. Initial development took place before the war, entering service in 1940. Eventually over 4,000 Würzburgs of various models were produced...

 in 1941. However the SCR-584 developed the system much further, and added an automatic tracking mode. Once the target had been detected and was within range, the system would keep the radar pointed at the target automatically, driven by motors mounted in the antenna's base.

The system could be operated at four frequencies between 2,700 and 2,800 MHz (10–11 cm wavelength), sending out 300 kW pulses of 0.8 microseconds in duration with a pulse repetition frequency
Pulse repetition frequency
Pulse repetition frequency or Pulse repetition rate is the number of pulses per time unit . It is a measure or specification mostly used within various technical disciplines Pulse repetition frequency (PRF) or Pulse repetition rate (PRR) is the number of pulses per time unit (e.g. Seconds). It...

 (PRF) of 1,707 pulses per second. It could detect bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...

-sized targets at about 40 miles range, and was generally able to automatically track them at about 18 miles. Accuracy within this range was 25 yards in range, and 0.06 degrees (1 mil) in antenna bearing angle (See Table "SCR-584 Technical Characteristics"). Because the electrical beam width was 4 degrees (to the -3db or half-power points), the target would be smeared across a portion of a cylinder, so as to be wider in bearing than in range (i.e., on the order of 4 degrees, rather than 0.06 degrees implied by the mechanical pointing accuracy), for distant targets. Range information was displayed on two "J-scopes", similar to the more common A-line display, but arranged in a radial pattern timed to the return delay. One scope was used for coarse range, the other for fine.

For detection, as opposed to tracking, the system also included a helical scanning mode that allowed it to search for aircraft. This mode had its own dedicated PPI
Plan position indicator
The plan position indicator , is the most common type of radar display. The radar antenna is usually represented in the center of the display, so the distance from it and height above ground can be drawn as concentric circles...

 display for easy interpretation. When used in this mode the antenna was mechanically spun at 4 rpm while it was nudged up and down to scan vertically.

Operational use

Although the first operational unit was delivered in May 1943, various bureaucratic problems led to it being delayed in being delivered to the front-line troops. The SCR-584 was first used in combat at Anzio
Anzio
Anzio is a city and comune on the coast of the Lazio region of Italy, about south of Rome.Well known for its seaside harbour setting, it is a fishing port and a departure point for ferries and hydroplanes to the Pontine Islands of Ponza, Palmarola and Ventotene...

 in February 1944, where it played a key role in breaking up the Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....

's concentrated air attacks on the confined beachhead. The SCR-584 was no stranger to the front, where it followed the troops, being used to direct aircraft, locate enemy vehicles (one radar is said to have picked up German vehicles at a distance of 26 kilometers), and track the trajectories of artillery shells, both to adjust the ballistic tables for the 90 millimeter guns, and to pinpoint the location of German batteries for counter-battery fire. The SCR-584 was not, however, used in the rapidly-shifting very front lines, where lighter, less accurate, radars such as the AN/TPS-1 were used.

The SCR-584 was so successful that it was adapted for use by the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

. CXBL, a prototype of the navy version, was mounted on the carrier USS Lexington
USS Lexington (CV-16)
USS Lexington , known as "The Blue Ghost", is one of 24 s built during World War II for the United States Navy. The ship, the fifth US Navy ship to bear the name, is named in honor of the Revolutionary War Battle of Lexington...

 on March 1943, while the production version, the SM, built by General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...

, was operational on the carriers USS Bunker Hill
USS Bunker Hill (CV-17)
USS Bunker Hill was one of 24 s built during World War II for the United States Navy. The ship, the second US Navy ship to bear the name, was named for the Battle of Bunker Hill. Bunker Hill was commissioned in May 1943, and served in several campaigns in the Pacific Theater of Operations, earning...

 and USS Enterprise
USS Enterprise (CV-6)
USS Enterprise , colloquially referred to as the "Big E," was the sixth aircraft carrier of the United States Navy and the seventh U.S. Navy ship to bear the name. Launched in 1936, she was a ship of the Yorktown class, and one of only three American carriers commissioned prior to World War II to...

 by October 1943. A lighter version of the system was also developed, the SCR-784
SCR-784
The SCR-784 was a fire control radar set used by the U.S. Army designed to be an amphibious version of the SCR-584, and mounted on a searchlight trailer called a K-84.- Statistics :Frequency: 2,800 MHzPulse Width: 0.8 µsecondsPulse Repetition Rate: 1707 pps...

. The only real difference was that the new design weighed 12,000 lb
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...

, whereas the original was 20,000.

Davenport waterproofed a number of the radar sets so that they could be carried aboard the Allied armada launching the Normandy landings on D-Day
D-Day
D-Day is a term often used in military parlance to denote the day on which a combat attack or operation is to be initiated. "D-Day" often represents a variable, designating the day upon which some significant event will occur or has occurred; see Military designation of days and hours for similar...

.

After the war, the radar was adapted for use in the AN/MPQ-12, and AN/MPM-38 systems, a US Army field artillery missile system (MGM-5 Corporal
MGM-5 Corporal
The MGM-5 Corporal missile was the first guided weapon authorized by the United States to carry a nuclear warhead.The first nuclear-authorized unguided rocket was the MGR-1 Honest John...

). A modified version was also used to control and beacon-track (using an onboard transponder) the CORONA
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...

 spy satellite.

Despite using vacuum tubes and being powered by an analog computer, some specimens of the SCR-584 are still operational today. One is found at the National Severe Storms Laboratory
National Severe Storms Laboratory
The National Severe Storms Laboratory is a National Oceanic and Atmospheric Administration weather research laboratory located at the National Weather Center in Norman, Oklahoma....

 in Norman, Oklahoma, where the 584 pedestal is the platform for the new Shared Mobile Atmospheric Research & Teaching Radar, or SMART-R.

Automatic gunlaying (using, among others, the SCR-584 radar) and the proximity fuze
Proximity fuze
A proximity fuze is a fuze that is designed to detonate an explosive device automatically when the distance to target becomes smaller than a predetermined value or when the target passes through a given plane...

 played an important part in Operation Diver
Operation Diver
Operation Diver was the British codename for their countermeasures against the V-1 flying bomb campaign launched by the German Luftwaffe in 1944 against London and other parts of Britain...

, (the British operation to counter the V1 flying bombs). Both of these had been requested by AA Command and arrived in numbers, starting in June 1944, just as the guns reached their free-firing positions on the south eastern coast of England. Seventeen per cent of all flying bombs entering the coastal 'gun belt' were destroyed by guns in the first week on the coast. This rose to 60 per cent by 23 August and 74 per cent in the last week of the month, when on one extraordinary day 82 per cent were shot down. The rate increased from one V-1 for every 2,500 shells fired to one for every hundred.

In 1953, the SCR-584-Mod II was used for tracking the Redstone (rocket)
Redstone (rocket)
The PGM-11 Redstone was the first large American ballistic missile. A short-range surface-to-surface rocket, it was in active service with the U.S. Army in West Germany from June 1958 to June 1964 as part of NATO's Cold War defense of Western Europe...

, its range extended to 740 km by the use of an onboard transceiver.

K-83 dolly

an additional accessory was the K-83 dolly, built by GE, it could be attached to the semitrailer hitch so that smaller vehicles could move the unit around.

See also

  • AN/MPQ-14
  • SCR-784
    SCR-784
    The SCR-784 was a fire control radar set used by the U.S. Army designed to be an amphibious version of the SCR-584, and mounted on a searchlight trailer called a K-84.- Statistics :Frequency: 2,800 MHzPulse Width: 0.8 µsecondsPulse Repetition Rate: 1707 pps...

  • List of U.S. Signal Corps Vehicles
  • Signal Corps Radio
    Signal Corps Radio
    Signal Corps Radios were U.S. Army military communications components that comprised "sets". Under the Army Nomenclature System, SCR initially designated "Set, Complete Radio," and later "Signal Corps Radio," though interpretations have varied over time....

  • G-numbers
  • Gun Data Computer
    Gun Data Computer
    The gun data computer is a series of artillery computers used by the U.S. Army, for coastal artillery, field artillery, and antiaircraft artillery applications...


External links

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