Vietnam War

===Radio communications===
[[File:North Vietnamese SA-2.jpg|thumb|North Vietnamese SAM crew in front of SA-2 launcher. The Soviet Union provided North Vietnam with considerable anti-air defense around installations.]]

The Vietnam War was the first conflict where U.S. forces had [[secure voice]] communication equipment available at the tactical level. The National Security Agency ran a crash program to provide U.S. forces with a family of security equipment, codenamed [[NESTOR (encryption)|NESTOR]], fielding 17,000 units initially; eventually 30,000 units were produced. However, limitations of the units, including poor voice quality, reduced range, annoying time delays and logistical support issues, led to only one unit in ten being used.<ref name="NSA">{{Cite web |year=1981 |title=A History of U.S. Communications Security; the David G. Boak Lectures |url=https://www.governmentattic.org/18docs/Hist_US_COMSEC_Boak_NSA_1973u.pdf |publisher=National Security Agency |page=43 |volume=2|archiveurl=https://web.archive.org/web/20230326032806/https://www.governmentattic.org/18docs/Hist_US_COMSEC_Boak_NSA_1973u.pdf|archive-date=March 26, 2023}}</ref> While many in the U.S. military believed that the Viet Cong and PAVN would not be able to exploit insecure communications, interrogation of captured communication intelligence units showed they could understand the jargon and codes used in real time and were often able to warn their side of impending U.S. actions.<ref name=NSA/>{{Rp|4,10}}