1957-1961 I Corps headquarters became operational at Danang on 1 June 1957 and was responsible for the area from Danang north to the DMZ. US advisors at I Corps headquarters consisted of about a dozen officers and enlisted men with a colonel of infantry as senior corps adviser, and two lieutenant colonels to advise the corps engineer, armor, ordnance, and signal units.
1962 In January, the
United States Army's 93rd Transportation Company (Light Helicopter), equipped with
H-21C Shawnees was deployed to
Da Nang Air Base. In early September 1962, the
United States Marine Corps (USMC)
Operation Shufly helicopter squadron, equipped with
HUS-1s (UH-34s) began redeploying with its support units from
Soc Trang Airfield in
IV Corps to Da Nang Air Base, completing the redeployment by 20 September. Simultaneously, the U.S. Army's 93rd Helicopter Company moved from Da Nang to Soc Trang.
1964 Following the
1963 South Vietnamese coup d'état, coup leader General
Dương Văn Minh reassigned
II Corps commander General
Nguyễn Khánh to command I Corps, allegedly to get him as far from
Saigon as possible. On 30 January 1964, Khánh
overthrew Minh in a bloodless coup. By 6 March, Khánh had replaced three of the four Corps commanders. When Johnson opted to replace Flaming Dart's tit-for-tat retaliatory strikes with
Operation Rolling Thunder in late February, a violent reaction from North Vietnam now deemed more likely. As a result, on 8 March the
9th Marine Expeditionary Brigade (9th MEB) went ashore to defend Da Nang Air Base. In the Combined Campaign Plan for 1966, which the JGS and MACV issued in December, the allies declared their "basic objective" for the year to be clearing, securing, and developing the heavily populated regions around Saigon, in the Mekong Delta, and in selected portions of the I and II Corps coastal plain. "Coincident" with this effort, they would defend significant outlying government and population centers and conduct search and destroy operations against "major VC/PAVN forces." In pursuit of these objectives, South Vietnamese forces would concentrate on defending, clearing, and securing the designated strategic areas. American and third-country forces, besides securing their own bases and helping to protect rice-producing areas, were to "conduct operations outside of the secure areas against VC forces and bases." Implicit in these words was the de facto division of labor between the South Vietnamese and Americans that had been in effect since the summer.
1966 On 17 January, the USMC
1st Marine Regiment headquarters arrived at Chu Lai as the lead element of the
1st Marine Division to be deployed to South Vietnam. From 28 January to 17 February, III MAF and the 2nd Division conducted
Operation Double Eagle in southern Quảng Ngãi province. Dinh proved either unwilling or unable to restore the normal tempo of combat operations. During a visit to the zone on 1 May, Westmoreland found crowds of local combat troops in the streets of Huế and Da Nang and rejected Dinh's assertion that the political situation there was settling down.
1967 From 27 January to 7 April, the
3rd Battalion, 7th Marines conducted
Operation Desoto in the Đức Phổ District. From 1 February to 18 March, the 3rd Marine Division conducted
Operation Prairie II along the DMZ. By the end of July, PAVN/VC activity had declined in the Corps as they regrouped for attacks around the September elections. Their plans called for assaults in each of the five northern provinces, together with a demonstration along the DMZ intended to attract large numbers of US forces to its defense. During the summer lull, the VC 1st and 2nd Regiments, both weakened, departed from Quang Ngai province. The former rejoined the 2nd Division up in Quang Tin, while the latter traveled south to rejoin the 3rd Division in Binh Dinh. From 20 October to 16 February 1968, four USMC battalions conducted
Operation Osceola in the Hải Lăng Forest and around
Quang Tri Combat Base. From 28 to 30 September, the PAVN
attempted to overrun the CIDG's
Thường Ðức Camp. In response to this, the 1st Marine Division launched
Operation Maui Peak from 1 to 19 October. From 15 December to 28 February 1969, the 196th Infantry Brigade conducted
Operation Fayette Canyon in "Antenna Valley", Hiệp Đức District. At the end of 1969, Major general
Melvin Zais, commanding US
XXIV Corps in I Corps, proposed breaking up the 1st Division (with four regiments and about nineteen combat battalions) into two divisions controlled by a "light corps" headquarters responsible for the defense of the DMZ area, but his immediate superior, Lieutenant general
Herman Nickerson Jr. (USMC), commanding III MAF (and the I Corps senior adviser) and Lãm, both vetoed the idea, citing the lack of enough experienced Vietnamese officers to staff a new command. On 14 April, the 3rd Marine Amphibious Brigade was activated and it assumed control of all III MAF units remaining in South Vietnam.
1972 On 27 January, a USAF gunship flying at above the former Khe Sanh Combat Base was shot down by an
SA-2 missile. In late January 1973 elements of the PAVN 263rd SAM Regiment, equipped with SA-2 missiles, deployed to Khe Sanh. The regiment had four firing battalions and one support battalion, each firing battalion having four to six launchers and occupying one firing site. From 29 July to 11 November, the 3rd Division, Airborne Division and 12th Ranger Group fought five PAVN regiments in the
Battle of Thượng Đức. To compensate for the loss of the Airborne brigades, Trưởng ordered the Marine Division to redeploy from its position near Huế to the Da Nang area. In the midst of confusion over the defensive strategy and the growing civilian panic, PAVN forces crossed the Thach Han River, attacked and occupied the ruins of Quang Tri City. The South Vietnamese forces resisted and then fell back on 19 March. Trưởng was recalled to Saigon on 19 March to brief Thiệu on his withdrawal plan. Trưởng had developed two contingency plans: the first was predicated on government control of Highway 1, which would be utilized for two simultaneous withdrawals from Huế and Chu Lai to Da Nang; the second presupposed PAVN interdiction of the highway and called for a withdrawal into three enclaves: Huế, Da Nang, and Chu Lai. This was to be only an interim measure, however, since the forces that withdrew to Huế and Chu Lai would then be sea-lifted to Da Nang by the navy. Thieu then stunned Trưởng by announcing that he had misinterpreted his previous orders, Huế was not to be abandoned, and the Marine Division was to be withdrawn from MR1 to reconstitute the general reserve. The PAVN halted at the My Chanh Line and then moved the weight of their assault to the west and south of Huế. Early on the morning of 21 March the lead battalions of the 324B and 325th Divisions, together with the independent Tri-Thien Regiment, with heavy artillery support, assaulted South Vietnamese positions from the Bo Corridor to Phu Loc. Heavy artillery fire fell on Huế. On 22 March, after back and forth fighting over Nui Bong near Phu Loc, the PAVN captured the mountain allowing them to interdict Highway 1. The population of Huế declined to only 50,000, and the Hai Van Pass was clogged with desperate people trying to escape south with more than 100,000 refugees inundating Da Nang. On 23 March the 913th RF Group started an unauthorized withdrawal from the My Chanh Line causing panic among other forces and a general rout developed. At 18:00 on 24 March, with the PAVN closing in on Huế, Trưởng decided to abandon Huế and evacuate as many troops as possible along the
Phú Vang district a narrow coastal sandspit east of Highway 1, where they could move without restriction until reaching the evacuation column north of Hai Van Pass. The effort proved futile, and as panic grew, the withdrawal, compounded by PAVN pressure became a rout. On 24 March, Quang Ngai and Tam Ky fell to the PAVN. On 25 March, the PAVN captured Hoi An. On the night of 25 March the sealift from Chu Lai began. Panic quickly took over as soldiers fought for places on the first boats. Sufficient order was restored, however, to move about 7,000 soldiers up to Da Nang. The remnants of the 4th Infantry and the almost nonexistent 6th Infantry were regrouped on Ly Son Island, while the 12th Ranger Group, down to only 500 men, and the few remaining soldiers of the 5th Infantry, were assembled near Da Nang. This left Da Nang as the last line of defense. The massive influx of civilian refugees into the Da Nang area precipitated a breakdown in law and order. Attempts to establish a defensive perimeter around the city met with little success, and on 30 March, by now in total chaos, Da Nang collapsed with barely a shot being fired. Trưởng and his staff swam to a boat and were evacuated to Saigon and the PAVN occupied all of MR1 which ceased to exist. ==Divisions==