[3] 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.

The 1st Cavalry Division began operations against VC and PAVN forces in Bình Định shortly after its arrival in South Vietnam in September 1965.

[6] 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 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.

[4]: 263–9 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.

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.

[8]: 89–92 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.

To improve control of these forces, on 9 January he established a forward division command post at LZ Hammond (14°04′34″N 109°02′38″E / 14.076°N 109.044°E / 14.076; 109.044), 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.

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.

Miller's men cautiously entered the cave and discovered many connecting tunnels that led to exits and storage areas for food, equipment, and ammunition.

They found an unusual collection of records, including a complete local order of battle; personnel rosters; weapons and equipment lists; ammunition supply status reports; and a map showing the locations of caches throughout the province.

Over the next several days, repeated attempts to destroy the rest of the complex were only partially successful, so the engineers finally settled for sealing the entrances.

The main supply route for the 1st Cavalry Division during Thayer II had extended north from Qui Nhơn over Highway 1 to LZ Hammond.

In December a second supply base was built at Landing Zone English, on the southern Bồng Sơn Plain, just 5 km north of the Lai Giang, to support the 2nd Brigade.

A combination of heavy rain and air traffic soon reduced the top layer of earth under the airstrip's steel matting to a thin mud that squirted up through the mesh and obscured the pilots' vision and made the runway extremely slippery.

Deep ruts quickly developed underneath the steel surface, forcing the partial closure of the aerial supply terminal throughout January.

Because of English's unreliability as a fixed-wing supply base, the 1st Cavalry Division increased its normal three-day stockage level at Hammond to five days as insurance against heavy rains washing out the roads.

During the last two weeks of January the ARVN fought two major battles against the 7th and 8th Battalions of the 22nd Regiment and, with timely American assistance, claimed to have killed or captured over 250 PAVN.

Then, on 2 February Norton received an agent report indicating that two PAVN battalions would attack Pony, an American firebase in the northern Kim Son Valley, sometime during the next seven days.

In view of what had happened at Bird in the same general area, Norton reacted quickly and airlifted the 3rd Brigade headquarters with one battalion from Camp Radcliff to Pony.

Another intelligence source, a defector from the 9th Battalion, 22nd Regiment, revealed that his unit was understrength but had plenty of ammunition and was planning to attack English after the Têt truce, between 8 and 12 February.

On 6 February the ARVN 40th Regiment, 22nd Division, met a PAVN battalion 4 km north of English and routed it in a short, violent fight.

Throughout these inconclusive engagements, General Norton impatiently waited at his new command post at Landing Zone Two Bits, 3 km south of English, for the truce to end.

However, another Department of Defense report said that "Refugee movement is highly visible evidence of the failure of the government to protect the rural population from the Viet-Cong.