AN/URC-117 Ground Wave Emergency Network

GWEN was part of the Strategic Modernization Program designed to upgrade the nation's strategic communication system, thereby strengthening the value of nuclear deterrence. The GWEN communication system, established in the late 1980s, was designed to transmit critical Emergency Action Messages (EAM) to United States nuclear forces. EMP can produce a sudden power surge over a widespread area that could overload unprotected electronic equipment and render it inoperable. In addition, EMP could interfere with radio transmissions that use the ionosphere for propagation. It was thought that GWEN would use a ground-hugging wave for propagation and so be unaffected by the EMP. The first major phase of construction was called the "thin line" which began in 1985. ==Operations==

Command and control messages originating at various military installations were transmitted on the 225 to 400 MHz band and received by a network of unmanned relay stations, called "Relay Nodes", dispersed throughout the contiguous 48 states. The Relay Nodes would re-transmit these command and control messages to each other, and to Strategic Air Command operating locations and launch control centers using low frequencies in the 150-175 kHz range in order to take advantage of ground-hugging radio propagation similar to commercial AM radio stations. Problems Early in its lifetime, electrical interference problems caused by GWEN system operation began to surface. Since the stations were using LF, the chosen frequency was within 1 kHz of the operating frequency of nearby electrical carrier current systems. With GWEN handling constant voice, teletype and other data traffic, it caused interference to the power companies' diagnostic two kilohertz side carrier tone. When the side carrier tone disappeared due to interference from GWEN, the power grid would interpret that as a system fault. ==Site layout==

The overall area of a GWEN Relay Node was approximately , approximately × 700 feet. It was surrounded on the perimeter by locked, chain-link fences topped with barbed wire. Typical site features included: • A main Longwave transmitting tower (generally between tall • A radial network of underground wires forming a large ground plane to serve as a reflecting surface for radio waves • Three electronic equipment shelters; two located near the perimeter of the site, and one at the base of the tower containing an antenna-tuning unit (ATU) • UHF and LF receive antennas mounted on either a 10 ft. mast, 30 ft. light pole, or 60–150 ft. tower. • A diesel backup generator, with a two-chambered fuel tank having a capacity of The main GWEN antenna operated intermittently in the LF band at 150 to 175 kilohertz (kHz) (below the bottom of the AM broadcast band at 530 kHz). The peak broadcasting power was from 2,000 to 3,000 watts. The UHF antenna operated at 20 watts, between 225 and 400 megahertz (MHz). ==GWEN site locations==

A 1998 U.S. Department of Transportation environmental impact survey that proposed repurposing a number of existing GWEN sites for use by the Nationwide Differential Global Positioning System listed the locations of 29 GWEN sites: • Appleton, Washington • Austin, Nevada • Bakersfield, California • Billings, Montana • Bobo, Mississippi • Clark, South Dakota • Edinburg, North Dakota • Fenner, California • Flagstaff, Arizona • Gettysburg, Pennsylvania • Goodland, Kansas • Grady, Alabama • Great Falls, Montana • Hackleburg, Alabama • Hagerstown, Maryland • Hawk Run, Pennsylvania • Kirtland AFB, New Mexico • Klamath Falls, Oregon • Macon, Georgia • Medford, Wisconsin • Medora, North Dakota • Onondaga, Michigan • Penobscot, Maine • Pueblo, Colorado • Ronan, Montana • Savannah Beach, Georgia • Spokane, Washington • Summerfield, Texas • Whitney, Nebraska ==Termination==

Some of the initial towers had prompted groups of citizens in Massachusetts, Oregon, Pennsylvania, and California to organize to fight construction of GWEN towers in their areas. The groups believed that the presence of a GWEN node would increase the community's "strategic worth" in the eyes of the Soviet Union and thus invite attack. Responding to these groups, the Air Force repeatedly downplayed the importance of the towers, stating they were not worth that kind of attention by the Soviet Union. In 1994, new construction of GWEN towers were banned after a defense appropriations bill eliminated any funding for the towers for one year. A few months later, the United States Air Force announced that they would terminate the construction contract to build the remaining 25 towers, except for the money used to dismantle the system. ==Gallery==

File:GWEN antenna tuning unit shelter and security fence.PNG|GWEN antenna shelter & security fence File:GWEN equipment area.PNG|GWEN equipment area File:Essex, CA GWEN site 1.jpg|Former GWEN tower, Essex, California File:GWEN Essex CA updated GPD diff gear 1.jpg|GPS gear added to former GWEN tower at Essex, California File:Essex CA, GWEN rf rad warning sign.jpg|RF radiation warning sign on former GWEN site at Essex, California ==See also==