Operation Thayer (13 September 1966 – 1 October 1966), Operation Irving (2 October 1966 – 24 October 1966) and Operation Thayer II (24 October 1966 – 11 February 1967) were related operations with the objective of eliminating People's Army of Vietnam (PAVN) and Viet Cong (VC) influence in Bình Định Province on the central coast of South Vietnam. The operations were carried out primarily by the United States (US) 1st Cavalry Division against PAVN and VC regiments believed to be in Bình Định. South Korean and Army of the Republic of Vietnam (ARVN) forces also took part in the operation.
The sustained operations were deemed a success by the US, which claimed that more than 2,500 PAVN/VC killed at a loss of about 329 American dead. Many areas under PAVN/VC influence were abandoned by the rural population as non-combatants fled the fighting or were forced by American and South Vietnamese forces to leave their homes. The PAVN/VC were able to break up into smaller units and evade open-battle against an overwhelming air-land-sea deployment of US forces, and much like in Operation Masher which preceded it, they were able to return and contest the region once the operation had died down.
Background Bình Định Province, on the central coast of South Vietnam, was a long-time communist stronghold with the VC, and increasingly the PAVN, controlling most of the rural areas. Bình Định, with a population of about 875,000, was characterized by a heavily populated narrow coastal plain out of which rose several mountain massifs. Inland, the many rivers ran through narrow valleys separated by heavily forested mountains. The area of the province was . The ARVN controlled little more than the larger towns and Highway 1, the main north–south thoroughfare of South Vietnam, and Highway 19 which led from the coast to the highland city of Pleiku.
The 1st Cavalry Division began operations against VC and PAVN forces in Bình Định shortly after its arrival in South Vietnam in September 1965. From its base at Camp Radcliff near An Khe, Gia Lai Province, the 1st Cavalry had launched operations several operations into nearby Bình Định Province which resulted in large numbers of PAVN/VC soldiers being killed in search and destroy missions, but, with the withdrawal of US forces from the province after each incursion, the PAVN/VC quickly reestablished their control or influence over many rural areas in the province.
On the night of 3 September 1966 a VC platoon launched a mortar attack on Camp Radcliff. The base was hit by 119 mortar rounds over a 5-minute period, killing 4 soldiers and wounding 76, while 77 out of the 1st Cavalry's 400-plus helicopters were damaged. The VC were believed to have escaped. In early September, the PAVN/VC also attacked several ARVN military bases and ambushed an ARVN convoy. The attacks illustrated the fragility of the control of the area by the South Vietnamese government and the need to suppress the PAVN/VC forces.
Operation Thayer and follow-on operations Irving and Thayer II were called the "Binh Dinh Province Pacification Campaign" and had the objective "to clean up, once and for all, all regular PAVN/VC units in the area as well as uprooting the long established VC infrastructure."
Operation Thayer
Operation Thayer was the largest air assault undertaken up until that time in the Vietnam War. The focus of Operation Thayer was the Kim Son Valley where seven small rivers, separated by mountains, came together in what the Americans called the Crow's Foot. The 1st Cavalry had previously encountered stiff resistance in the Crow's foot during Operation Masher in February 1966. It now appeared that the PAVN/VC had re-established their base areas. After two days of B-52 air strikes near the valley, on 13–14 September General John Norton airlifted 5 battalions into the highlands surrounding the Kim Son valley. The Americans then descended into the valleys, hoping to catch large numbers of PAVN/VC in their net. They found few enemies to fight, but determined that the PAVN/VC forces in the Kim Son valley had escaped to the east.
Operation Thayer ended on 1 October. The Americans claimed to have killed 231 PAVN/VC at a loss to themselves of 35 dead and missing. Contrasting the success of this operation, was S.L.A. Marshall who privately declared that Operation Thayer I was a "complete bust", that artillery was shooting at "clay pipes" that the enemy was "either not there or so adroit and clever" as to completely avoid US search-and-destroy and that from first-hand observation that the 231 killed was a complete fabrication.
Operation Irving
Operation Irving immediately followed Operation Thayer. The focus of the offensive moved east to the small mountain ranges near the coast of Bình Định where the PAVN 12th Regiment which had fled the Kim Son Valley was believed to be. To "find, fix, and finish" the PAVN Norton had five American, five South Korean and 2 South Vietnamese battalions, a total of some 6,000 men. Each national contingent would search a different mountain massif rising more than out of the coastal plain over a north–south area of more than and extending more than inland from the sea. The allied forces attempted to prevent the PAVN/VC from exfiltrating this area.
A problem faced in Operation Irving was the large number of non-combatants, mostly farmers, in the heavily populated coastal area. Leaflets and radio programs instructed the civilians to stay put in their villages or if caught in a battle for the village to leave only in the direction of allied soldiers.
Operation Irving had an immediate success on 2 October. The Americans observed PAVN/VC in the village of Hoa Hoi, near the coast, and sent in by helicopter a platoon-sized group to investigate. The platoon took heavy fire and suffered casualties and reinforcements were rushed to the area to encircle the village. Villagers were offered the opportunity to leave Hoa Hoi and about 200 did. Nightfall came before an attack could be organized. The US Navy offshore fired illumination shells all night to prevent the PAVN from escaping through the American lines.
The next morning two American companies advanced on the village from the north, forcing the PAVN to either stand and fight or to attempt to break through the Americans lines encircling the village. The American attackers searched and destroyed the village and rooted out the PAVN. By the end of the day, the battle was over. The Americans claimed to have killed 233 PAVN and taken 35 prisoners out of a total force of 300 men. American losses were six dead.
Following the successful Hoa Hoi battle, the 1st Cavalry searched for additional PAVN/VC forces, shifting the focus westward to the mountainous Kim Son and Suoi Ca valleys. The South Korean and South Vietnamese forces also clashed with the PAVN/VC, the South Vietnamese, with US helicopter gunship support, accounting for 135 PAVN/VC in a battle on 13 October. The Allied forces, however, could not find and bring to battle large elements of PAVN/VC.
Operation Irving was declared a great success, with the Allies claiming they had killed 681 PAVN/VC and captured 1,409 with losses to the allies of 52 dead The US accounted for 681 of those killed, while suffering 19 dead. The success of this operation contrasted with previous ones, but this was described as "result of a fluke shot" rather than a deliberate search and destroy, noting the previous battles in which the US rarely had tactical or strategic initiative against the PAVN/VC.
Operation Thayer II
Operation Thayer was focused on searching the Kim Son valley and southwards to the Suoi Ca Valley for PAVN/VC, which were believed to have broken into smaller units due to the successes of Operation Irving. The operation was hampered by heavy monsoon rains which impacted both American and PAVN/VC forces. In early December the decision was taken to empty the Kim Son Valley of its non-combatants and declare it a free fire zone in which any unidentified person was considered to be a combatant and unrestricted artillery and air strikes were permitted. About 1,100 people were forced or enabled to leave the valley. Many others chose to stay, either because they were VC loyalists or refused to abandon their homes and land. On December 17, American forces fought a battle east of the Kim Son valley, killing 95 PAVN/VC at a cost of 34 American dead and three helicopters shot down.
The PAVN/VC demonstrated they were still capable of offensive action with an attack on Firebase Bird in the contested Kim Son Valley. The firebase had been hurriedly constructed and, due to a Christmas truce, had less than one-half of its authorized manpower present. Bird was occupied by C Battery 6th Battalion, 16th Artillery and B Battery, 2nd Battalion, 19th Artillery and defended by elements of the 1st Battalion, 12th Cavalry. On the early morning of 27 December after preparatory mortar fire Bird was attacked by 3 Battalions of the 22nd Regiment. The PAVN quickly breached the perimeter and occupied all the 155mm and some of the 105mm gun pits. The remaining guns of 2/19 Artillery were then used to fire Beehive rounds directly at the PAVN stopping the attack. Supporting artillery fire was called in from nearby Firebase Pony () and helicopter gunships also arrived to give supporting fire, forcing the PAVN to retreat The 1st Cavalry sent in a battalion of troops to pursue the retreating attackers. US losses in the attack were 27 dead and 67 wounded. The US estimated that PAVN/VC losses in the attack and pursuit were 267 dead.
To prepare for the move into northern Bình Định, General Norton continued to consolidate his position farther south during Thayer II. He assigned Colonel James Shanahan's newly arrived 3rd Brigade, 25th Infantry Division to the Suoi Ca and Vinh Thanh Valleys, regions known to contain an important enemy trail complex. Norton retained his 1st Brigade in the Kim Son Valley and assigned his 2nd Brigade responsibility for the Cay Giep and Mieu Mountains in the northern sector. To improve control of these forces, on 9 January he established a forward division command post at LZ Hammond (), 40 km northwest of Qui Nhon.
On 19 January in the Suoi Ca Valley, patrols from one of Shanahan's units, the 1st Battalion, 14th Infantry Regiment, discovered a series of caves among large granite boulders. Double- and triple-canopied vegetation hid the caves from aerial observation. They turned out to be the VC political headquarters for Bình Định Province. The Americans heard the voices of women and children coming from one cave and ordered them out. When there was no response, a company commander and one of his sergeants crept in and found themselves in a large cavern. The company commander was shot dead and the sergeant dragged the body out. Immediately, the battalion commander, Lt. Col. William H. Miller, had his men surround the area and used Tear gas and smoke grenades to flush out the cave. As the smoke swirled, the VC fired rifles and lobbed grenades out of the entrance. Only after flamethrowers depleted the oxygen and suffocated those within did the resistance end.