North Vietnamese regulars are fighting in South Vietnam - Jul 14, 1964 - HISTORY.com

U.S. military intelligence publicly charges that North Vietnamese regular army officers command and fight in so-called Viet Cong forces in the northern provinces, where Viet Cong strength had doubled in the past six months. Only the day before, South Vietnamese Gen. Nguyen Khanh had referred to the “invasion” by North Vietnamese Army (NVA) forces.

There would soon be other evidence that North Vietnamese troops were operating in South Vietnam. In August, South Vietnamese officials would claim that two companies from the North Vietnamese army had crossed the Demilitarized Zone in Quang Tri province. A battle ensued, but the North Vietnamese forces were defeated with heavy casualties. It became known later that Hanoi had ordered its forces to begin infiltrating to the South. This marked a major change in the tempo and scope of the war in South Vietnam and resulted in President Lyndon B. Johnson committing U.S. combat troops. North Vietnamese forces and U.S. troops clashed for the first time in November 1965, when units from the newly arrived 1st Cavalry Division engaged several North Vietnamese regiments in the Battle of the Ia Drang Valley in the Central Highlands.