page_title: US signals intelligence in the Cold War
section_title: The buildup: 1965-1967
hierarchical_section_title: US signals intelligence in the Cold War / 1960s / US operations in Southeast Asia / The buildup: 1965-1967
caption_attribution_description: SIGINT in SE Asia 1964-1968
context_page_description: After the end of World War II, all the Western allies began a rapid drawdown of military forces, including those of signals intelligence. At the time, the US still had a COMINT organization split between the Army and Navy. A 1946 plan listed Russia, China, and a [redacted] country as high-priority targets.
  Each service ran independent agreements with foreign counterparts, some of which, especially the British, had already formed a central communications intelligence organization. Lack of centralization bothered these allies. The vital British-US cooperation was, at this point, one of the strongest incentives to the US Army and Navy to form a centralized organization.
context_section_description: After a regiment of PRC MiG-17 fighters arrived at Mengtzu in 1963, SIGINT predicted jet fighters would enter the DRV air defense network. This was reinforced with learning that high-level DRV and PRC personnel would have a meeting at Mengtzu in May 1964.
  The Gulf of Tonkin incident, in August 1964, involved two-destroyer DESOTO patrols equipped with intercept vans, backed up with carrier air patrols
  .
  Early DRV Air Defense Buildup
  In the weeks immediately following the Gulf of Tonkin incident, the most important SIGINT role was providing defensive information to US air strikes. This was done at three levels of generality. First, overall monitoring of the DRV air defense network, SIGINT could maintain situational awareness of North Vietnamese tracking via radar and visual observers. Second, SIGINT detected the activation of specific weapons systems in the air defense network, such as SA-2 surface-to-air missiles (SAM), anti-aircraft artillery (AAA), and fighter interceptors. Finally, it could detect immediate threats, such as missile launches or impending attacks by fighters.
  Reports from the roughly 40 visual observation stations were sent to sector headquarters, which controlled AAA. These reports were sent by high-frequency (HF) Morse code radiotelegraphy, in standardized message formats where only the specific details needed to be transmitted. It could take up to 30 minutes for a report to work its way through the system, so that more specific tracking or interception orders could be given. According to the NSA history, air defense communications did not change significantly during the war, so COMINT analysts were able to become very familiar with its patterns and usage.
  Command and control applied to four system components: air warning from radar and observer stations, limited radar tracking, AAA and SAMs, and fighters. Rapid upgrades started to go into place after the Gulf of Tonkin incident, with the arrival, within two days, of 36 MiG-15 and MiG-17 fighters. These arrived from China and were probably flown, at first, by Chinese pilots, but Vietnamese pilots were soon in familiarization flights.
  Two main communications links between the DRV and PRC were established, from Hanoi to Kuangchow and K'unming. These liaison networks allowed access to Chinese radar covering the Gulf of Tonkin, Laos, and Hainan Island, as well as the DRV itself. By 1967-1968, there were approximately 110,000 persons in the DRV air defense system, supporting 150 radars, 150 SAM sites (rarely all active at the same time), and 8,000 AAA pieces. There were 105 fighters, including the MiG-21. At any given time, one-third to one-half of the fighters were based at PRC airfields.
  Air Defense headquarters was at Bach Mai Airfield. By January 1966, all major air defense installations, including those in the PRC, were linked by a common HF radio network with standardized procedures. There was an Air Situation Center and an Air Weapons Control Staff. The latter assigned targets to the various defense weapons.
  A wider range of communications systems emanated from Air Defense Headquarters, including VHF voice, landlines, and HF/MF. Due to the need to move information quickly, without any automation, most communications were either in low-grade ciphers or were unencrypted.
  The DRV system matures, 1965
  North Vietnam's air defense system, as of 1965, had three main subsystems:
  Radar detection and tracking
  Situational awareness (senior controller at Bac Mai)
  Tactical fighter direction (Phuc Yen, Gia Lam, Kép)
  Airborne fighters
  SAMs and AAA
  In 1965, the DRV had full radar coverage, with Chinese input, out to 150 miles (240 km) from its borders. Detection and processing times dropped to five minutes. In contrast, the US did not have full radar coverage over the DRV, and SIGINT was seen as a way of filling the gaps in US knowledge of their air defense operations.
  Intensified USAF SIGINT
  Under several code names, the last being UNITED EFFORT, the earlier combination of Okinawa-, and then Bien Hoa (Vietnam) based RB-47H ELINT aircraft and drones, originally plan
caption: SIGINT-related events, 1964-1968
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