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.