Eight years later, on another hot and sticky spring night, I would lie in bed in that same hotel with the sound of incoming rockets landing in the city. And when my helicopter rose from the American embassy at dusk on the war’s last day the airport really was under attack, and the fires I saw burning on the ground really were the ravages of war.

But that March, 50 years ago this month, the mood of American officials was all upbeat, get-on-the team optimism. We were winning. Secretary of Defense Robert McNamara famously said that “every quantitative measurement we have shows we are winning the war.” From Ambassador Henry Cabot Lodge in his elegant white suits to Gen. William Westmoreland in his starched and immaculately creased uniforms, the word was that even the most hardened doubters would become believers before the year was out.

Two years earlier President Lyndon B. Johnson had escalated the war, replacing mere advisers with main force fighting units, with more American troops and equipment pouring into the country every day. The Communists responded in kind: 1967 saw the war changing from Viet Cong “punji” stakes of sharpened bamboo and booby traps to North Vietnamese infantry battalions backed by heavy Russian artillery firing from across the Demilitarized Zone, one of the war’s more ironic oxymorons. A.R.V.N., the Army of the Republic of South Vietnam, would still go on fighting, but it was America’s soldiers that would now be taking the lead, easing our Vietnamese allies to the side. It was America’s war now.

It would be my job to make some sense of all of this, and I spent the next several months crisscrossing the country, in the rice fields of the Mekong River delta, with the well-equipped American Army in the forested hills of the Central Highlands and with the Marine Corps in the northern reaches of South Vietnam. I rode in Jeeps, trucks, four-engined transport planes and countless helicopters in and out of fire fights, often riding in with ammunition resupply and out with the American dead zipped in their body bags.

But mostly I traveled on foot with the soldiers, getting to know officers and enlisted men. I saw how elusive the enemy could be, how devastating our fire power, and how McNamara’s quantitative measurements were an illusion. The military called these operations “search and destroy” missions, but it became clear to me that although we could destroy, we could not win. With every village burned we were making more enemies, and despite our frequent bombing north of the DMZ there was no evidence that the other side was going to quit.