With South Vietnam in chaos, hardliners in Hanoi seize the initiative and send combat troops to the south, accelerating the insurgency. Fearing Saigon’s collapse, President Johnson escalates America’s military commitment, authorizing sustained bombing of the north and deploying ground troops in the south.
http://www.pbs.org/video/the-river-styx-january-1964-december-1965-wayhiw/