Editing Ho Chi Minh trail (section)

==Operation Commando Hunt (1968–1970)==
{{further|topic=the interdiction campaign|Operation Commando Hunt}}
{{further|topic=the electronic sensor system|Operation Igloo White}}

[[File:HCMT70.png|thumb|upright=1.5|The Ho Chi Minh Trail, 1970.]]
In the wake of the Tet Offensive, the North Vietnamese expanded and modernized their logistical effort. The number of supply and maintenance personnel dropped, mainly due to increased use of motor and river transport and mechanized construction equipment. The CIA estimated during the year that the 559th Group was using 20 bulldozers, 11 road graders, three rock crushers, and two steamrollers for maintenance and new road construction.<ref name=Prados/>{{RP|193}}

As many as 43,000 North Vietnamese or Laotians were engaged in operating, improving, or extending the system.<ref name=Nalty/>{{RP|37}} In 1969, 433,000 tonnes of ordnance fell on Laos.<ref name=Prados/>{{RP|303}} This was made possible by the end of "Operation Rolling Thunder" and the commencement of "Operation Commando Hunt" in November 1968. U.S. aircraft were freed for interdiction missions and as many as 500 per day were flying over Laos. By the end of 1968, bombing missions over southern Laos had climbed 300 percent, from 4,700 sorties in October to 12,800 in November.<ref>{{cite book|last=Tilford|first=Earl|title=Setup: What the Air Force did in Vietnam and Why|publisher=Air University Press|year=1991|url=https://apps.dtic.mil/sti/pdfs/ADA421969.pdf|archive-url=https://web.archive.org/web/20210514064030/https://apps.dtic.mil/sti/pdfs/ADA421969.pdf|url-status=live|archive-date=14 May 2021|page=173}}{{PD-notice}}</ref>

This round-the-clock aerial effort was directed by "Operation Igloo White", run out of [[Nakhon Phanom Royal Thai Navy Base|Nakhon Phanom]], Thailand. It was composed of three parts: strings of air-dropped acoustic and seismic sensors collected intelligence on the trail; computers at the Intelligence Collection Center (ICS) in Thailand collated the information and predicted convoy paths and speeds; and an airborne relay and control aircraft which received the signals from the sensors and routed aircraft to targets as directed by the ICS.<ref name=Van/>{{RP|255–283}}

This effort was supported by MACV-SOG recon teams, who, besides carrying out recon, wiretap, and [[bomb damage assessment]] missions for "Commando Hunt", also hand-placed sensors for "Igloo White". Personnel interdiction was abandoned by early-1969. The sensor system was not sophisticated enough to detect enemy personnel, so the effort was given up until "Operation Island Tree" in late-1971. A revelation for U.S. intelligence analysts in late 1968 was the discovery of a petroleum pipeline running southwest from the northern port of [[Vinh]].<ref name=Prados/>{{RP|339–340}}

=== Fuel pipeline ===
Initially, fuel was carried by porters, but this was inefficient and time-consuming, and thus highlighted the need to extend the pipeline at a much faster rate. The responsibility to build the pipeline fell to Lieutenant Colonel Phan Tu Quang, who became the first Chief of the Fuel Supply Department, and Major Mai Trong Phuoc, who was the Commander of Road Work Team 18, the secret name for the workers who built the pipeline.<ref name=Morris2006/>{{RP|92}}

Early in 1969, the pipeline crossed the Lao frontier through the [[Mu Gia Pass]] and, by 1970, it reached the approaches to the A Shau Valley in South Vietnam. The plastic pipeline, equipped with numerous small pumping stations, managed to transfer diesel fuel, gasoline, and kerosene all through the same pipe. Due to the efforts of the PAVN 592nd Pipelaying Regiment, the number of pipelines entering Laos increased to six that year.<ref name=Pribbenow/>{{RP|392}}

The 559th Group, still under the command of General Đồng Sỹ Nguyên, was made the equivalent of a Military Region in 1970 and the group was given the additional name, the "Truong Son Army". It was composed of four units, one division and three equivalent units: the 968th Infantry Division; 470th Group; 565th MAG; and 571st Rear Group.<ref name=Morris2006/>{{RP|59}} The units controlled fuel pipeline battalions.<ref name=Morris2006/>{{RP|168}}

In July 1971, the Truong Son Army was reorganized into five divisional headquarters: the 470th, 471st, 472nd, 473rd, and the 571st.<ref name=Morris2006/>{{RP|168}} The group consisted of four truck transportation regiments, two petroleum pipeline regiments, three anti-aircraft artillery (AAA) regiments, eight engineer regiments, and the 968th Infantry Division. By the end of 1970 the 559th was running 27 "Binh Trams", which transported 40,000 tonnes of supplies with a 3.4% loss rate during the year.<ref name=Pribbenow/>{{RP|261}}

Colonel Quang and Major Phuoc would eventually build 5,000&nbsp;km of pipeline and ship over 270,000 tonnes of petrol. Sections of the pipeline were still in use in the 1990s.<ref name=Morris2006/>{{RP|92}}

=== Truck relay system ===
Trucked supplies traveled in convoys from North Vietnam in relays, with trucks shuttling from one way station to the next. The vehicles were then unloaded and reloaded onto "fresh" trucks at each station. If a truck was disabled or destroyed, it was replaced from the assets of the next northern station and so on until it was replaced by a new one in North Vietnam. Eventually, the last commo-liaison station in Laos or Cambodia was reached and the vehicles were unloaded. The supplies were then cached, loaded onto watercraft, or man-portered into South Vietnam.<ref name=Nalty/>{{RP|218}}

Due to the increased effectiveness of "Commando Hunt", North Vietnamese transportation units usually took to the roads only at dusk with traffic peaking in the early morning hours. As U.S. aircraft came on station, traffic would subside until just before dawn, when fixed-wing gunships and night bombers returned to their bases. The trucks then began rolling again, reaching another peak in traffic around 06:00 as drivers hurried to get into truck parks before sunrise and the arrival of the morning waves of U.S. fighter bombers.<ref name=Nalty/>{{RP|218}} By the last phase of "Commando Hunt" (October 1970 – April 1972), the average daily number of U.S. aircraft flying interdiction missions included 182 attack fighters, 13 fixed-wing gunships, and 21 B-52s.<ref name=Glister>{{cite book|last=Glister|first=Herman|title=The Air War in Southeast Asia: Case Studies of Selected Campaigns|publisher=Air University Press|year=1993|url=https://apps.dtic.mil/sti/pdfs/ADA421686.pdf|archive-url=https://web.archive.org/web/20220125082216/https://apps.dtic.mil/sti/pdfs/ADA421686.pdf|url-status=live|archive-date=25 January 2022}}{{PD-notice}}</ref>{{RP|21}}

[[File:North Vietnamese Antiaircraft Weapons.jpg|thumb|upright=1.35|The evolution of PAVN [[anti-aircraft weapon]]s, 1965–1972.]]

The North Vietnamese also responded to the American aerial threat by the increased use of heavy concentrations of anti-aircraft artillery. By 1968 this was mainly composed of 37&nbsp;mm and 57&nbsp;mm radar-controlled weapons. The next year, 85&nbsp;mm and 100&nbsp;mm guns appeared, and by the end of ''Commando Hunt'', over 1,500 guns defended the system.<ref name=Prados/>{{RP|313}}

Of all the weapons systems used against the trail, according to the official North Vietnamese history of the conflict, the [[AC-130 Spectre]] fixed-wing gunship was the most formidable adversary. The Spectres "established control over and successfully suppressed, to a certain extent at least, our nighttime supply operations".<ref name=Pribbenow/>{{RP|261}} The history claimed that allied aircraft destroyed some 4,000 trucks during the 1970–71 dry season, of which the C-130s alone destroyed 2,432 trucks.<ref name=Pribbenow/>{{RP|261}}

A Spectre countermeasure was unveiled on 29 March 1972, when a Spectre was shot down on a night mission by a surface-to-air [[SA-7]] missile near Tchepone.<ref name=Prados/>{{RP|369}} This was the first U.S. aircraft shot down by a SAM that far south during the conflict. PAVN responded to U.S. nighttime bombing by building the 1,000 kilometer-long Road K ("Green Road") from north of Lum Bum to lower Laos. During "Commando Hunt IV" (30 April–9 October 1971), U.S., South Vietnamese and Laotian forces began to feel the North Vietnamese reaction to General [[Lon Nol]]'s coup in Cambodia and the subsequent closure of the port of [[Sihanoukville (city)|Sihanoukville]] to its supply shipments.<ref>{{cite book|last=Shawcross|first=William|title=Sideshow: Kissinger, Nixon, and the Destruction of Cambodia |date=1979 |publisher=Simon & Schuster |isbn=9780671230708|pages=112–127|url=https://books.google.com/books?id=RasqAAAAYAAJ}}</ref> As early as 1969 PAVN had begun its largest logistical effort of the entire conflict.<ref name=Glister/>{{RP|20}}

The Laotian towns of [[Attapeu]] and [[Salavan (city)|Salavan]], at the foot of the [[Bolaven Plateau]] were seized by the PAVN during 1970, opening the length of the Kong River system into Cambodia. Hanoi also created the 470th Transportation Group to manage the flow of men and supplies to the new battlefields in Cambodia.<ref name=Prados/>{{RP|191}} This new "Liberation Route" turned west from the trail at Muong May, at the south end of Laos, and paralleled the Kong River into Cambodia. Eventually this new route extended past Siem Prang and reached the [[Mekong River]] near [[Stung Treng]].<ref name=Pribbenow/>{{RP|382}}

During 1971 PAVN took Paksong and advanced to [[Pakse]], at the heart of the Bolaven Plateau region of Laos. The following year, Khong Sedone fell to the North Vietnamese. The PAVN continued a campaign to clear the eastern flank of the trail that it had begun in 1968. By 1968, U.S. Special Forces camps at [[Khe Sanh Combat Base|Khe Sanh]] and Khâm Đức, both of which were used by MACV-SOG as forward operations bases for its reconnaissance effort, had either been abandoned or overrun. In 1970, the same fate befell another camp at [[Dak Seang Camp|Dak Seang]]. What had once been a {{convert|20|mi|km|-1|order=flip|adj=mid|-wide}} supply corridor now stretched for {{cvt|90|mi|km|-1|order=flip}} from east to west.{{citation needed|date=October 2021}}