Repeatedly during my years in Vietnam, senior military officers didn’t believe me when I told them their unit was about to be attacked. The troops believed me—I was working side by side with them and they saw what I and my fellow SIGINTers were doing, intercepting and exploiting North Vietnamese communications. But colonels and generals couldn’t grasp how a handful of guys, known more for their spit than their polish and abetted by a civilian under cover as a soldier, could use radios and a tangle of antennas to divine the intentions of the enemy.
After many instances, I came to call the recurrence of nonbelief “the Cassandra Effect,” named after the Greek mythological heroine who was given the gift of true prophecy and cursed with never being believed.
Maybe the most monumental case was in the highlands in the autumn of 1967—the battle of Dak To. Through intercepted communications, I could see that several North Vietnamese divisions had covertly moved into position and were preparing to assault the U.S. 4th Infantry Division and the 173rd Airborne Brigade. I warned the commanders, but they waved me away in disbelief.
Then the enemy struck. One battalion was virtually destroyed. The U.S. counterattacked, and one of the largest battles of the Vietnam war followed. By the time it was over, both sides had suffered huge numbers of casualties, but no ground had changed hands.