The Buildup: 1965-1967
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 Bac Mai. 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, Kep)
- 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 planned for Cuba, was tried again in 1964, but without the blip-enhancing electronics that would make the North Vietnamese think it was a U-2. The North Vietnamese did not take the bait. Eventually, in 1966, the North Vietnamese shot down a drone, but everything worked and the entire electronic score of the SA-2 symphony was recorded.
Some of the first airborne SIGINT platforms were C-130 QUEEN BEEs, operational by early 1965. They flew two monitoring orbits, one over northwest Thailand and the other over the Gulf of Tonkin. Apparently, there was never a satisfactory basing arrangement for them, although they worked with analysts at Da Nang. Redactions make it impossible to understand their full pattern, but they did, under undefined circumstances, land at Da Nang. Also in early 1965, a large number of US Air Force Security Service (USAFSS) moved from the Philippine Islands (PI) to the Republic of Vietnam.
While the RB-47H's were retired after the 1966 success, the RC-135Ms of the 82nd Strategic Reconnaissance Squadron moved from Japan to Okinawa, in the 4252 Strategic Wing. Tasking increased until those SIGINT platforms were flying daily, then 24-hour coverage under the COMBAT APPLE program, still flying a weekly mission against China or Russia.
COMBAT APPLE missions initially flew over the Gulf of Tonkin, including a refueling station just south of the Demilitarized Zone. The location of the refueling position allowed them to continue collecting SIGINT while drawing fuel from the tanker.
Often just after the COMBAT APPLEs refueled, North Vietnamese MiG-21 fighters would try a single supersonic pass at the COMBAT APPLE aircraft, firing everything and immediately turning back, almost out of fuel. The ungainly RC-135's were heavily loaded and had little ability to maneuver, and no defensive systems. Luckily, none were lost, but carrier-based fighters were soon ordered to escort them. There was a period during which the Navy aircraft fell into a pattern of leaving the RC-135 for their own refueling, and the North Vietnamese tried more attacks when the US fighters flew away. Eventually, better tactics were evolved, including using multiple fighter flights and the RC-135 as bait in what turned out to be an ambush for the MiGs, from a pair of fighters that flew in close formation with the RC-135 and did not show separately on radar.
Obviously, this constant workload stressed the RC-135M's, which periodically had to go back to the US for major maintenance. Attempts were made to fill the vacancy with RC-135D's from Alaska, but aircraft from there, aside from having smaller engines, did not adapt to the tremendously different climate
While ELINT helped against the SAM threat, the first kill of a US aircraft by an SA-2 SAM took place in mid-1965. The DRV air defense network was improving, and, by the end of 1965, were processing tracking reports in 5 minutes, a procedure that previously took 30 minutes.
The classic battle between national-level SIGINT and direct support of operations occurred, and a compromise was reached to put a 7th Air Force SIGINT Support Group at Da Nang. Still, many SIGINT units moved from Vietnam to Udon, Thailand, between 1965 and 1967.
- Ship-based SIGINT
Dedicated SIGINT ships, built on merchant hulls, were also used, but proved too vulnerable and slow. An intermediate size, such as Pvt Jose F. Valdez (T-AG-169) operated around Africa from 1961 until 1969. Valdez was too slow to reach the patrol area to which the Liberty was sent. The larger Belmont-class included the USS Liberty (AGTR-5), attacked by Israel in 1967. Modern ship installations generally involve intercept stations in mobile vans, which can be put onto the deck of a warship, which can protect itself as the Pueblo and Liberty could not. Why this level of protection was not available in 1967 is difficult to understand.
Starting in 1965 and continuing until the end of the AGTR program in 1969, two "technical research" SIGINT ships, AGTR-1 Oxford and AGTR-2 Jamestown, sailed up and down the coast of Vietnam, acting as "firemen" to fill gaps in land-based coverage. They also participated in calibrating airborne direction finding.
During this time period, the Medal of Honor was bestowed on the captain of the AGTR-5, USS Liberty, for his leadership following an Israeli attack on his ship.
A class of even smaller vessels included the Banner-class, including the USS Pueblo (AGER-2), captured by North Korea in 1968.
- Second-generation Army tactical SIGINT aircraft (part 1, see 1970s for continuation)
In 1968, the Army introduced the RU-21D LAFFING EAGLE, as an incremental improvement in the long series of RU-21 aircraft, still operational today. The aircraft were technical improvements over their predecessors, but were very maintenance intended. After American forces withdrew from South Vietnam, some RU-21D's went to Thai bases, and all returned to the US in 1975.