English: Diagram of a Ground Wave Emergency Network relay node. GWEN was a survivable command and control communications network operated by the US military between 1982 and 1993 designed to ensure that messages from national command authority, such as nuclear launch orders, would reach US military facilities in the aftermath of a nuclear strike. It consisted of a network of unmanned radio relay "nodes" at 150-200 mile intervals throughout the US which forwarded messages on 150-175 kilohertz in the low frequency (LF) band. Radio transmissions in this band are relatively unaffected by the W:electromagnetic pulse (EMP) created by nuclear weapons that disrupt other electronic devices. The node consists of a UHF receiver and a 2 kilowatt low frequency transmitter driving a 299 ft high, umbrella antenna.