Continuing with Body of Secrets by James Bamford...

In the penultimate days before the North Korean attack on the Pueblo, NSA's focus was on another troubled land severed along a degree of latitude: Vietnam. For the 2 million people packed as tightly as bullet casings into the twenty square miles of Saigon, the morning of January 22, 1968, began with a frenzy of activity. Emergency vehicles, rushing to a trio of separate terrorist incidents, performed pirouettes around fruit laden shoppers. Overhead, a swarm of helicopter gunships, like heavily armed locusts, searched back and forth across an open field for Communist guerrillas. In front of a cloud of hazy blue exhaust fumes, an American-made tank tore at a downtown pavement as the driver took a shortcut to a convoy of vehicles heading north.

Amid the war, life went on as normal. At a restaurant near the Central Market, passersby inspected the barbecued chickens with their shiny lacquer like coatings, hanging from hooks in an open window. U.S. Air Force commandos in big hats and low-slung revolvers sipped bitter espresso at a stand-up counter, like gunslingers at a Wild West saloon. In the malodorous Ben Nghe Canal, gray wooden sampans pushed slowly past shacks perched on narrow, spindly legs. Policemen in tropical whites directed swirls of traffic at the broad circular intersections.

In the far north on that Monday in January, at Firebase 861 near Khe Sanh, enemy soldiers lobbed mortar rounds and rifle grenades. American troops fought back through mailboxlike slits in the thick cement walls that protected them. Between explosions, a Marine battalion arrived to reinforce the garrison. Landing nearby were pallets containing 96,000 tons of ordnance. The day before, North Vietnamese Army forces had begun a siege of the hilltop outpost, and the United States was engaged in an all-out effort to save it.

In charge of the American war was Army General William Westmoreland. On the afternoon of January 22, at his Saigon headquarters, his major worry was the powerful attack in the north on Khe Sanh. He compared it to the bloody assault on the French at Dien Bien Phu more than a dozen years earlier. But Westmoreland was intent on proving that massive firepower would allow the United States to succeed where the French had dismally failed. He believed that sometime prior to Tet— the Vietnamese New Year, nine days away—the guerrillas would launch a major attack in the far north, at Khe Sanh and some of the surrounding bases.
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