1966 to 1967 

In the late 1960s, the United States began to escalate its military involvement in Vietnam.

In 1966, the number of United States military personnel in Vietnam topped 300,000. This influx of troops into South Vietnam was countered by the DRV with an increased presence of Viet Cong—an insurgent group of communist forces that operated separately from, but under the direction of the regular North Vietnamese army, called the People’s Army of Vietnam (PAVN). Operating within the Republic of Vietnam since the signing of the Geneva Accords of 1954, the Viet Cong recruited soldiers in South Vietnam throughout the war.

In 1967, American and South Vietnamese forces focused on eliminating the Viet Cong with Search and Destroy missions below the 17th parallel.  During these operations, a massive tunnel system was discovered, used by communist forces to move men and supplies south to aid the Viet Cong. By the end of 1967, U.S. Secretary of Defense Robert MacNamara testified before Congress that the movement of supplies from north to south had not slowed as a result of United States military actions.