The Ground Wave Emergency Network (GWEN) was a command and control communications system intended for use by the United States government to facilitate military communications before, during and after a nuclear war. Specifically, the GWEN network was intended to survive the effects of an electromagnetic pulse from a high-altitude nuclear explosion and ensure that the United States President or their survivors could issue a launch order to Strategic Air Command bombers by radio. AN/URC-117 was the system's Joint Electronics Type Designation System identifier, which signified various radio components installed in different locations. Each GWEN Relay Node site featured a longwave transmitting tower, generally between tall, and emitting an RF output of between 2,000 and 3,000 watts. Of 240 planned GWEN towers, only 58 were built. In 1994, a defense appropriations bill banned the funding of new GWEN tower construction, and a few months later, the GWEN program was cancelled by the US Air Force. The United States Coast Guard later outfitted a number of former GWEN sites to house the Nationwide Differential GPS system. History 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 network was conceived as an array of approximately 240 radio transceivers distributed across the continental USA which operated in the Low frequency (LF) radio band. Analysis showed that low-frequency (150-190 kilohertz) radio transmissions were largely unaffected by high-altitude EMP, and the Air Force Weapons Laboratory (Kirtland Air Force Base) tested a small scale 'groundwave' transmission system in 1978-1982. Based on the groundwave concept's promise, USAF Headquarters issued a draft Program Management Directive (PMD) for a "Proliferated Groundwave Communications System (PGCS)" on 25 August 1981. The name of this proposed network system was changed from PGCS to Groundwave Emergency Network in February 1982 The Air Force placed a tentative initial operating capability for GWEN by January 1992. When doubts arose regarding the threat of electromagnetic