The U.S. military presence in Vietnam increased regularly between 1960 and 1964. American combat troops were not present, but military advisors were assisting South Vietnamese forces. In 1964, the North Vietnamese attacked U.S. vessels in the Gulf of Tonkin, an area of the South China Sea bordered on the west by Vietnam and on the north by China. Johnson asked Congress for a resolution to increase U.S. military involvement without a formal declaration of war. The measure was passed by both houses.

By February 1965, U.S. planes began regular bombing raids over North Vietnam. On March 6, 1965, American marines landed at the South Vietnam port city of Da Nang, and by year's end the United States stationed two hundred thousand combat troops in Vietnam. Here is the text of Johnson's report to the nation on August 4, 1964, concerning the Gulf of Tonkin incident.

My...