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The SCR-584 was a mobile medium-range radar unit used to provide aircraft position information to the AAAIS and fire control data to antiaircraft gun batteries through a director. When coupled with an IFF system, the unit could recognize friendly aircraft transmitting the appropriate signal. The SCR-584 was commonly used in conjunction with the M7 director for fire control of the four 90mm guns in a battery, but could also be connected to the older M4 director for units so equipped. However, its full potential was realized when paired with the more advanced M9/M10 director system.
Among the most significant technological developments of the war, the SCR-584 was based on the British cavity magnetron, introduced to American leaders and scientists by the Tizard Mission in September 1940. The groundbreaking magnetron was refined into a new type of radar through the collective genius assembled at the Radiation Laboratory, based at the Massachusetts Institute of Technology.
The SCR-584 was a momentous milestone in radar technology and provided deadly accurate gun-laying on unseen targets. In combination with the electromechanical M9 director, this radar represented the cutting edge in antiaircraft equipment. The unit was also highly mobile, able to be set up and placed in service at a given location in about thirty minutes (compared to the two to six hours required for the SCR-268).
Successful field testing of the SCR-584 prototype took place in April 1942, and the War Department immediately ordered further development and procurement. By April 1944, the allotment of SCR-584 units allocated to antiaircraft gun battalions was being increased. AAA gun battalions usually were equipped with five SCR-584 units - one for each of the four firing batteries plus one additional radar to be used for surveillance and as a spare.
The maximum scan range of the SCR-584 was 70,000 yards, but the unit was considered less accurate at ranges exceeding 50,000 yards. Although highly advanced for its day, the SCR-584 did have some difficulty picking up low flying aircraft, although not to the degree of long-wave radars. The availability of spare parts for units in the field was also a nagging issue. Nevertheless, the radar unit made an immediate positive impact on antiaircraft effectiveness wherever it was introduced - Italy, England, and the Pacific. Compared to the earlier SCR-268 set, the SCR-584 was significantly less susceptible to jamming and other radar countermeasures. Many field units were retrofitted with an N2 gate, which improved the radar's accuracy, reduced interference from ground clutter, and rendered the SCR-584 even less vulnerable to jamming. By the end of the war, the SCR-584 was in widespread use as a gun layer, searchlight controller, and weather radar. The versatile unit was also very effective in providing data for ground control intercept of hostile aircraft and the direction of air strikes on ground targets.
INSIDE THE SCR-584 TRAILER
The range operator (seated left) is ready to adjust the range tracking handwheel to properly position a target echo on the right-hand oscilloscope of the pair visible just above his head. When the echo is correctly placed, the targeted airplane can be isolated for automatic tracking. The range indications of these two scopes added together yields the slant range to the target. The range operator will continue to make fine adjustments, even as the SCR-584’s parabolic antenna automatically follows the enemy aircraft.
The PPI operator (seated right) is looking down to monitor the plan position indicator (PPI) oscilloscope, which is mounted directly in front of him on the sloped panel, and thus is not visible in this photograph. He will also observe the azimuth and elevation indicator dials in front of him at eye level. The PPI operator looks for any indication that the selected target is changing course. He is also watchful for the close approach of additional aircraft, which might affect the scan and corrupt the tracking data. If another aircraft comes too near the targeted airplane, the operators could hit a COAST button that will allow the antenna to continue to follow the intended target's course while temporarily ignoring received signals for a period of four seconds - just enough time to allow the interfering aircraft to pass.
The control switch mounted on the sloped panel between the two operators selects one of the four modes in which the SCR-584 can operate – PPI SCAN, MANUAL, AUTOMATIC and REMOTE. Visible in the rack to the left of the range operator are (top to bottom) the automatic tracking unit, range unit, and the receiver.
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