The terrain within I Corps favored the enemy. The rugged, jungle-blanketed mountains that cover the western pan of the region hid Communist supply bases and the camps of main force units and facilitated the infiltration of North Vietnamese replacements and reinforcements. East of the mountains, a narrow rolling piedmont quickly gives way to a flat, wet coastal plain much of which is covered by rice paddies and beyond which lie beaches of the South China Sea. Most of the Vietnamese inhabitants of I Corps live in the flatlands, either in the thousands of villages and hamlets interspersed among the rice fields or in the large cities of Hue and Da Nang. Concealed among the civilians were the enemy's political agents and guerrillas, and from the populated areas the enemy drew recruits and supplies.

An estimated 78,000 enemy troops operated in I Corps. According to allied intelligence, the Communist order of battle included about 49,000 North Vietnamese Army (NVA) regulars, perhaps 6,000 main force Viet Cong (VC), over 12,000 VC guerrillas, and about 11,000 supply and administrative personnel. Almost half of these troops, some 42 infantry and 11 support battalions, were believed to be massed along or near the DMZ, while the second largest concentration-16 combat and 4 support battalions-threatened Da Nang in Quang Nam Province.

Three different headquarters directed enemy operations in I Corps. The B5 Front controlled the troops along the DMZ; Military Region (MR) Tri Thien Hue had charge of Quang Tri and Thua Thien Provinces; and MR 5 oversaw the campaign in the rest of I Corps, assisted by a separate headquarters subordinated to it, Front 4, which was responsible for Quang Nam. American and South Vietnamese intelligence officers believed that all three of these commands received orders directly from Hanoi, rather than through the Central Office for South Vietnam (COSVN), which commanded the enemy troops in the other three corps areas.

A year of heavy and constant allied pressure, guided by improved intelligence and by an increasingly sophisticated understanding of the enemy's methods and weaknesses, had left the NVA and VC in I Corps battered and exhausted at the end of 1969. Here, as elsewhere in South Vietnam, the allied war effort at last seemed to be moving forward steadily and systematically. Throughout the year, American, ARVN, and Korean troops had driven deep into well-established enemy base areas. They had inflicted heavy losses on main force units, seized or destroyed tons of supplies, and wrecked carefully constructed fortifications, bunkers, and tunnel complexes. At the same time, an intensified pacification campaign had reduced enemy guerrilla strength. By the end of the year, according to the statistical hamlet evaluation system then being used, about 90 percent of the civilians in I Corps lived in secure localities.

Especially impressive to American commanders in I Corps was the improvement of the South Vietnamese regular and militia forces. The ARVN, benefiting from intensive American efforts to improve its equipment, training, and leadership, had displayed increasing willingness and ability to seek out and engage the enemy. While still short of heavy artillery, aircraft, and good small-unit commanders, the ARVN divisions were steadily moving closer to assuming the burden of combat. The RFs and PFs, in the words of Major General Ormond R. Simpson, who finished a tour in command of the 1st Marine Division late in 1969, "they have a long way to go, but they're coming on strong." Rearmed with M16 rifles and often reinforced by combined action Marines these once unreliable troops were fighting with increasing effectiveness against the small enemy units that prowled the populated lowlands.

The North Vietnamese and Viet Cong were still able to mount heavy attacks, especially in northern I Corps, but supply shortages and growing allied combat effectiveness were increasingly forcing them to revert to harassing tactics. During late 1969, the number of engagements with major enemy units steadily declined while the number of rocket and mortar attacks and sapper raids on allied installations and civilian targets increased. In many pans of I Corps intelligence reports indicated severe shortages of food and medicine among the enemy. General Simpson declared in December 1969 that in Quang Nam "the enemy is in very bad shape at the moment. He is very hungry, he is ridden with malaria. Hunger is an over-riding thing with him, he is trying to find rice almost to the exclusion of anything else. He is moving to avoid contact rather than seek it." While the North Vietnamese and Viet Cong in I Corps and throughout South Vietnam remained determined to carry on the fight, their capacity to do so effectively showed every sign of declining.

Beginning in June 1969, the first two redeployments, codenamed Keystone Eagle and Keystone Cardinal, took out of Vietnam about 65,000 American military personnel including over 26,800 Marines. The entire 3rd Marine Division redeployed, as did one attack squadron, one observation squadron, and two medium and one heavy helicopter squadrons from the 1st MAW and proportional contingents of support and service troops.

In January 1970, the III Marine Amphibious Force (III MAF) was responsible for defense of the five northernmost provinces of South Vietnam. Constituting I Corps Tactical Zone (I CTZ), these provinces were from north to south Quang Tri, Thua Thien, Quang Nam, Quang Tin, and Quang Ngai. Marines had operated in these provinces since 1965 and had taken a valiant and costly part in some of the war's heaviest fighting, including the sieges of Con Thien and Khe Sanh and the house-to-house fighting in Hue City.