It was quiet in Saigon the night of Jan. 31, 1968, when Air Force Capt. David McNabb settled into his job as duty officer for a clandestine organization conducting special operations in the region.
Suddenly, explosions shattered the night, signaling an attack that would help turn public opinion back home against the war in Vietnam and bring American commanders to the realization they couldn't win it.
The night before, Army Col. John Singlaub — McNabb's commander and a founding member of the CIA — had ordered him to send a secret message to military leaders.
At 1:30 a.m. the next morning, the Tet Offensive will begin.
It happened just as predicted.
More than 80,000 enemy troops attacked more than 100 South Vietnamese locations.
"Oh yeah," recalled McNabb, 82, who now lives in Tampa. "It lit up the city."
He bristles at the notion that Tet was surprise attack, but he wouldn't know for 50 years whether his early warning did any good.
• • •
McNabb was working for a group that reported directly to the Pentagon — the Military Assistance Command, Vietnam, Studies and Observations Group, SOG for short. The command provided intelligence, conducted guerrilla warfare and ran covert "black" psychological operations, according to Singlaub, writing in his book Hazardous Duty.
McNabb found his way to the group after falling out of favor with a propaganda unit in Saigon for complaining to superiors about problems he saw.
"I had contrary opinions on many things, and I wasn't afraid to speak up."
First was a propaganda program that relied on college students from North Vietnam who were attending a Catholic university in South Vietnam and trying to persuade Buddhist villagers to support the government.
Next was the excessive volume of material handed out at one camp by the U.S. Agency for International Development. "I think it probably went to the Vietcong," the North Vietnamese guerilla group, he said.
His reward for blowing the whistle? "I was told do not do that sort of thing again."
Finally, in June 1967, McNabb got a chance to clear his name.
"They wanted me to show that B-52 strikes were rallying the Vietcong to the side of the South Vietnamese government."
But he didn't.
"My conclusion was that bombs dropped from 35,000 feet are probably counterproductive and looked like abject terror."
He was dismissed.
• • •
Thanks to contacts he made in the military mess halls of Saigon, McNabb found his way to the Studies and Observations Group.
With about 2,000 members at its peak, according to the Army, SOG had high casualty rates — more people killed and injured in 1968 than it had positions. Fifty members still are missing in action. Members received more than 2,000 individual awards for heroism, including 10 Medals of Honor and 23 Distinguished Service Crosses.
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McNabb became an action officer, helping recover U.S. personnel captured or missing in action. One way was distributing so-called "50 Kilos of Gold" pamphlets over Laos and North Vietnam, offering a reward for information.
In June 1967, with a half-million U.S. troops in Vietnam and anti-war protests raging back home, McNabb's unit released a message based on intelligence gathered by SOG: There would be a massive attack by the North Vietnamese Army and the Vietcong during the lunar New Year, known as Tet.
In November, with just a couple months to go, SOG sent out another message.
"It said that during the summer and fall, there had been a lot of infiltration into villages, hamlets and cities," McNabb said. "And that come the first week of Tet, they were going to use those people, plus supplies smuggled in during weddings and funerals, to launch a general attack."
The enemy "took great pains to conceal his intentions," according to a now-declassified CIA report from April 1968. Even most North Vietnamese soldiers taking part in the attack had no idea.
Still, few U.S. or Vietnamese officials believed the enemy would strike during Tet, according to the CIA document. Vietnamese military leaders let half their troops take leave for the holiday.
"There was good reason for this," according to the CIA document. "Tet symbolizes the solidarity of the Vietnamese people."
• • •
Solidarity was up in flames in Saigon by 1:30 a.m. Jan. 31.
As duty officer, it was McNabb's job to run communications and reach SOG personnel scattered around the capital.
"I started calling people and telling them we would pick them up."
But when Singlaub arrived around 2 a.m., he countermanded the order.
"Singlaub was very disappointed that the rest of the staff hadn't beaten him in. He said, 'I came here, they can come here.' "
McNabb, who finished his career in 1988 at MacDill Air Force Base as the first inspector general of U.S. Special Operations Command, said he has long wondered whether the warnings SOG issued had any impact beyond his command.
Army Gen. William Westmoreland, commander of U.S. forces in Vietnam, suspected a major attack, but not during Tet. After a premature strike the day before the Tet Offensive, he alerted commanders an attack was imminent, according to the CIA memo.
Intelligence developed by SOG did thwart the attack's objectives, the memo said: "With the exception of Hue, the enemy failed to hold any of his major military objectives."
• • •
Caught off guard, U.S. and South Vietnamese troops still regained most of the territory lost during Tet. But the offensive brought lasting damage to the war effort, weakening support for President Lyndon Johnson and generating news reports that showed no victory was imminent, according to the State Department historian.
In March 1968, Johnson halted the bombing of North Vietnam and announced he would not seek re-election. In April 1975, Saigon fell, ending a war that claimed the lives of 58,000 Americans and millions of Vietnamese.
Fifty years after the attack, McNabb said, he didn't know who paid attention to the intelligence developed by SOG.
When handed a copy of the CIA report, his eyes lit up.
"This gives me a sense of pride and success," he said. "It is a vindication of the fact that we knew what would happen."
Contact Howard Altman at email@example.com or (813) 225-3112. Follow @haltman.