SCR-270

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 1941 before the US entered World War II. SCR-270 Search Radar SCR-270 Search Radar Element Value Notes Nomenclature SCR-270/SR-271 Origins Variants SCR-270 A-D Mobile Versions SCR-271 A-D Fixed Versions 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 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 SCR-270 Set Up for Operation. Development Developed by Westinghouse/Western Electric for the US Army Signal Corps. Deployment Introduced in 1940 and was operationally deployed starting in 1941 before the US entered World War II. Among the first deployments were sets sent to the Canal Zone and to Hawaii. Six SCR-270 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 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. 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 fixed version required some infrastructure and construction to house the equipment. 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 12-inch displays provided a "A" scope 12-inch 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 wide by 9 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. The changes over the course of the war can provide a great disparity in photographs said to be of SCR-270/271 sites, for example compare the early mobile version pictured on page 11 of Searching the Skies with a later SCR-271 fixed site on page 13. Interior shots can also be vastly different. Compare the operating position of an early SCR-270 on page 12 with the twin 12" displays of later models. See Also: US Radar Sets Sources: Winkler, David F., Searching the Skies: the Legacy of the United States Cold War Defense Radar Program, USAF Hq Air Combat Command, 1997, 192 pages, Pdf, page 9-12. (includes photos) Links: Radomes - Radar Equipment USA Signal Corps OCS Assn - Radar Blooms