Operation Hong Kil Dong (July–August 1967): a converging attack on a mountain base and a trail gone cold

2026-10-13 · 1967-07-09 – 1967-08-26

Overview (BLUF)

On 9 July 1967 ROK forces in Vietnam began a converging attack with four Capital Division battalions and three 9th Division battalions on 'the Hub', a mountain area north-west of Tuy Hoa in Phu Yen Province. The objective was the PAVN 95th Regiment of the 5th Division. The US Army official history records it as the largest South Korean operation of the war (sources 1, 2).

In phase 1 the Koreans advanced no more than one or two kilometres a day and trapped several enemy companies in small base camps and caves. The 95th Regiment's main body was never fixed. Phase 2, which began on 12 August, failed to find the enemy division headquarters or the 188th Regiment. Meanwhile survivors of the 95th regrouped unobserved in the hills west of Tuy Hoa. The operation shows how much gaps in an encirclement and lost contact can decide the outcome in jungle mountains.

Background and Strategic Context

In 1967 the ROK forces' main task was securing the central coastal plain. In June the 95th Regiment left its base area and attacked South Vietnamese and Korean forces near Tuy Hoa. Its traditional redoubt was the Hub, north-west of Tuy Hoa, which US forces had also attacked in November 1966 (sources 1, 2).

ROK headquarters committed about 40% of its strength, seven battalions, and left about 60% on the coastal plain for security. This looks like a compromise: hunt enemy regulars in the mountains without giving up the protection of the populated coast. That split also shaped how long the operation could run and when it ended.

Terrain and Weather

The area of operations is jungle-covered mountains with almost no roads; the enemy used small base camps and caves. The Song Ba valley runs from Cung Son in the west down to Tuy Hoa, with the coastal plain to the east. To the north-west, the Ky Lo Valley leads to the Phu Yen–Phu Bon province border (figure 1).

Over jungle, air observation hardly worked, so finding the enemy came down to infantry on foot. High ground blocked radio traffic between battalions, and ammunition, food and water depended on helicopter resupply. The US 10th Combat Aviation Battalion supported both divisions directly from 9 July to 31 August (source 3). July and August fall before the region's rainy season, but daily weather records for the operation were not found.

Aerial photograph of Cung Son airfield in September 1967. The matted runway and parking apron sit on flat ground in the Song Ba valley, with hills beyond — Photo 1. Cung Son airfield (20 September 1967), the starting point of the 9th Division's three battalions. US engineers laid steel matting on the runway and apron in July and August — Photo: Office of History, US Army Corps of Engineers, public domain (US federal government work), via Wikimedia Commons

Forces and Dispositions

ROK: four Capital Division battalions attacked south-east from below Dong Tre; three 9th Division battalions attacked north-east from Cung Son. Two battalions of the ARVN 47th Regiment, 22nd Division, held blocking positions to the east on the edge of the coastal plain. B-52 strikes, division artillery and a US Army aviation battalion provided support (sources 1, 3).
PAVN: the 95th Regiment of the 5th Division was in the Hub. An intelligence estimate quoted in the US aviation report put the enemy in the western mountains at about 1,800 (source 3; report body not seen). The 5th Division headquarters and rear services were believed to be in the Ky Lo Valley to the north-west, and the 188th Regiment on the Phu Yen–Khanh Hoa border to the south.

Course of the Action

Figure 1. Operation Hong Kil Dong, sketch map (9 Jul–26 Aug 1967). Positions, borders and scale are approximate; enemy positions and movements are estimates — our own work, reconstructing the course from sources 1–3 on the scenario map

Converging attack and cordon (9 July – late July): the operation opened with B-52 strikes. First contacts were light. Both divisions advanced no more than one or two kilometres a day and trapped several enemy companies in small camps and caves.
Through the Hub (late July): all seven battalions swept east through the Hub. Resistance was strong at first, then almost vanished.
Lost contact (early August, about two weeks): there was almost no contact. Phase 1 ended with the clearing of enemy pockets bypassed during the advance (the date is not given in the sources).
Phase 2 searches (12–25 August): the Capital Division worked north-west up the Ky Lo Valley and reached the Phu Yen–Phu Bon border on the morning of the 25th without finding the headquarters or any rear installations. The 9th Division found no trace of the 188th Regiment on the Phu Yen–Khanh Hoa border.
End (late August): the troops returned to their coastal bases. Korean sources give 26 August as the end date (source 2).

Around this time the enemy raided Hieu Xuong district headquarters next to Tuy Hoa Air Base and pulled back. The official history dates the raid "9 August", which does not fit the order of its narrative (figure 2). Soon after the operation the 95th Regiment reappeared around hamlets west of Tuy Hoa, and the fighting of the following weeks brought heavy harm to residents and large-scale displacement (source 1). That phase lies outside the mountain operation and is not covered here or in the scenario.

Timeline of five phases from 9 July to 31 August 1967 as date bars: converging attack and cordon, sweep east through the Hub, about two weeks of almost no contact, phase 2 border searches on 12–25 August, return to the coast. Below: attack begins after B-52 strikes, 25 July phase 1 results report, district HQ raid of uncertain date, phase 2 begins 12 August, border reached 25 August, US aviation support ends 31 August — Figure 2. Operation Hong Kil Dong timeline. Dashed bars are periods whose start or end date is not given in the sources and are drawn approximately — our own work, based on sources 1–3

Decision Point Analysis

Decision 1: Pace of the advance (attacking force command, 9 July) After the B-52 strikes first contact was slight, and neither the enemy regiment's location nor the bombing's effect was known. The options were (a) a methodical advance of one or two kilometres a day, (b) a deep heliborne insertion onto the suspected regimental base, (c) halting to reconnoitre until the bombing was assessed, or (d) a fast advance along the ridges to close the ring early. The force chose (a), apparently to search a dispersed, hidden enemy thoroughly while keeping its own losses down. It trapped several enemy companies, but the slow tempo also gave the main body time to slip away. This is the first decision in the scenario.

Decision 2: Enemy in camps and caves (battalions and regiments, mid-July) Inside the ring, company-sized enemy groups were holed up in fortified camps and caves. The choices were (a) block the exits, reduce with fire and then clear, (b) bypass and keep moving, (c) assault the caves at once, or (d) call air and move on. The sources only say the enemy was "trapped", which reads closest to (a). Some pockets were bypassed and cleared at the end of phase 1. The details of cave clearing are not confirmed.

Decision 3: Avoiding battle and dispersing (PAVN 95th Regiment command) The 95th could (a) hold its base and fight it out, (b) disperse by company, delay and break away, or (c) infiltrate toward the coastal plain. Some companies were trapped, yet the main body was never fixed and survivors regrouped west of Tuy Hoa, so its course appears closest to (b). The routes by which it left before the ring closed are not confirmed by the sources.

Decision 4: Direction of phase 2 (ROK Field Force headquarters, 12 August) There had been no contact for more than two weeks, and the 95th's main body was lost. Options were (a) push north-west into the Ky Lo Valley after the enemy division headquarters, (b) return to the coastal bases and cover the approaches to Tuy Hoa, (c) search the hills west of Tuy Hoa with small units to find the 95th again, or (d) stay in the Hub and work suspected sites with fire. Headquarters chose (a) together with a search of the southern border, apparently reasoning that hitting command and support installations would stop the regiment recovering. Neither search found its target, and while the effort moved away from the coast the enemy regrouped in the hills close to it. The scenario's phase 2 decision and its final decision on ending the operation sit here.

Lessons

Encirclement and search and attack (FM 3-90): against a dispersed enemy, closing gaps matters more than speed. Unless pace and boundaries are matched with neighbouring units, the ring catches only part of the enemy.
Fires and assessment (FM 3-09): the claimed ROK results were attributed mainly to artillery, air and B-52 strikes (sources 2, 4). In jungle, the effect of fire can only be judged when someone on the ground checks it.
Intelligence and keeping contact: when the trail goes cold, find the enemy again before moving large units, and ask where a lost enemy will head and what the higher intent is protecting.
Sustainment: the deeper the valley, the smaller the landing zones and the longer the gaps between resupply. Supply capacity sets the reach of a mountain search.
Mission command (ADP 6-0): commanders from battalion up had to set the scope and end of the mountain operation within a higher intent centred on securing the coast.

Unresolved Questions

Enemy loss figures: the ROK report (over 700, with over 450 weapons captured) and the MACV count (638 dead, 88 captured) differ. All are ROK or allied claims, not independently verified (sources 1, 2, 4).
The date of the Hieu Xuong raid (printed as 9 August) does not fit the narrative order and may be a misprint.
Battalion and company detail, specific heliborne lifts and cave-clearing methods remain unconfirmed: the US aviation report and the Korean official history could not be consulted.
Participation of the 85th Regiment is stated only by Wikipedia and is unconfirmed.
The CMH official history PDF (source 1) blocked automated access (403); its content was checked against the page references cited by Wikipedia.

Want to command it yourself? Take the attacking force in this battle's training scenario and make the same decisions.

Sources

MacGarrigle, Combat Operations: Taking the Offensive, October 1966 to October 1967, U.S. Army Center of Military History (1998), pp. 311–314. https://history.army.mil/portals/143/Images/Publications/catalog/91-4.pdf (accessed 2026-10-13; automated access 403, checked via page references cited by Wikipedia)
Wikipedia, "Operation Hong Kil Dong" (cross-check; cites source 1 and MACV). https://en.wikipedia.org/wiki/Operation_Hong_Kil_Dong (accessed 2026-10-13)
10th Combat Aviation Battalion, Combat After Action Report, Operation Hong Kil Dong (1967), DTIC AD0387534 (search summary only; body 403). https://apps.dtic.mil/sti/pdfs/AD0387534.pdf (accessed 2026-10-13)
HQ MACV, "Review of significant events" (1967-08-20), p. 2, Texas Tech Vietnam Center (seen via Wikipedia citation). https://www.vietnam.ttu.edu/star/images/107/1070204003.pdf (accessed 2026-10-13)
U.S. Army, FM 3-90 Tactics, FM 3-09 Fire Support and Field Artillery Operations, ADP 6-0 Mission Command (publication index). https://armypubs.army.mil/ (accessed 2026-10-13)
Wikimedia Commons, Cung Son airfield photo file page (1967-09-20, public domain). https://commons.wikimedia.org/wiki/File:Cung_Son,_September_1967.png (accessed 2026-10-13)