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SCR-270 Long Range Search Radar Set - A World War II Long Range Search Radar set built by Westinghouse/Western Electric for the US Army Signal Corps. Introduced in 1940 and was operationally deployed starting in 1940 before the US entered World War II.

SCR-270 Mobile Search Radar with 8H X 4W Antenna, Set Up for Operation.
SCR-271 D Fixed Search Radar with Horizontal 4H X 8W Antenna modified for PPI Sweep and with IFF Antenna on top.

SCR-270 Search Radar

SCR-270 Search Radar
Element Value Notes
Nomenclature SCR-270/SCR-271
Variants SCR-270 A-D Mobile Ver
SCR-271 A-D Fixed Ver
Manufacturer Westinghouse
Western Electric
Type Search
Number Made 794
IEEE Band I Band
Frequency 104-112 MHz
Noise Figure Early versions 12db
Later Versions 6db
PRF 621 Hz
Pulse Width 10-25 usec
Azimuth Beamwidth 28 degrees
11 degrees
Original Ver
Later Ver
Rotation Speed Varies
Power 100 kW
Range 110 miles @ 25k Altitude
100 miles @ 20k Altitude
50 miles @ 5k Altitude
20 miles @ 1k Altitude
Long Range
(for the time)
Altitude 25 K
Introduced 1940

Early SCR-270 Mobile Search Radar, Operator Position in Truck.


Developed by Westinghouse/Western Electric for the US Army Signal Corps.


Introduced in 1940 and was operationally deployed starting in 1940 before the US entered World War II. Among the first deployments were sets sent to the Canal Zone (1940) and to Hawaii (1941). Six SCR-270 radar sets were in place at Hawaii on 7 Dec 1941 when the Japanese attacked Pearl Harbor. One set on the northern tip of Oahu at Opana Station spotted the attacking aircraft at 0702 as a large bloom on the radar at 132 miles out. Opana station was normally shut down during the daylight hours to conserve scarce vacuum tubes but remained operation that morning for additional training. At 0720 they reported the large approaching radar bloom to the information center at Fort Shafter but their information was not acted on and the attack commenced at 0800.

SCR-270D Mobile Search Radar Operator Console.

By the end of 1941, some 100 sets had been delivered and by the end of production in 1944 almost 800 sets had been produced.


Of the two major versions, the mobile version SCR-270 was the most used because it could be packed up and easily moved to new locations when conditions dictated. The complete set was carried in 4 to 6 vehicles, the largest measuring 30'4" x 9'10" x 8'. Total weight of shipment was 101,790 lbs; total volume 11,485 cu. ft. The mobile radar set could be operated from the transport trucks or could be removed and placed in a fixed facility. The truck-mounted configuration could be in operation about 6 hours after arrival. Site requirements included a height between 100' and 1000' above an unobstructed flat surface. The set could be operated by a seven-man operating crew. For 24 hour operation, about 50 men were required to run radar, communications, and the associated camp. Electrical power was furnished by a PE-74, 25 KVA gasoline-driven generator set.


The SCR-271 fixed Radar set came packed in 106 units, weighing a total of 42,279 lbs. The largest unit was 176″ x 25″ x 20″. Installation required a weatherproof building approximately 20′ x 40′ for housing radar components and a building approx. 20′ x 20′ for housing the power units and switchboard. A 100-foot tower on concrete footings was required for an SCR-271D and a 50-ft. tower for an SCR-271-3. Buildings and tower were built by engineers in about 3 weeks. The Radar could be installed by five men in about two weeks.


The SCR-270 evolved during the war from a relatively crude set with a single small 5-inch "A" scope display in the beginning to a rather substantial pair of 12-inch displays housed in a large cabinet. The larger displays provided a 12-inch "A" scope display and a 12-inch plan position indicator (PPI) display, the traditional centered, rotating range/azimuth display.

The antenna changed over time from a vertical flat array of dipole antennas 4 dipoles wide by 9 dipoles high to a more sensitive horizontal array of dipole antennas 8 wide by 4 high. The noise figure improved from 12 db to 6db, improving range and sensitivity. Modifications were required to the antenna when the PPI scope was added to synchronize the two.

The changes over the course of the war can provide a great disparity in photographs of SCR-270/271 sites, for example, compare the early mobile version pictured above with a later SCR-271 fixed-site above. Interior shots can also be vastly different. Compare the operating position of an early SCR-270 above with the twin 12" displays of later models above.

Partial SCR-270 Components List (edit list)
Component Model Quantity Height Width Deep Weight Notes
Transmitter BC-405 1 VT-122 Tube
Receiver BC-404 1 VT-123/128 Tubes
Oscilloscope BC-403 1 5" CRT Tube
15kV Power Supply RA-33/39/60 1 VT-141 Tubes
Spark Gap GA-4 1
IFF Set RC-151 1 Identification Friend or Foe (IFF)
Antenna Azimuth Speed Control 1
Antenna Mount Trailer K-22/K-64 1
Antenna 1 55'
Operations Van K-30 1
Power Generator Truck K-31 1
25 KVA Gasoline Motor/Generator Set PE-74 2
Flat Bed Truck K-22B 1

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