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bombing runs, once led Rivolo inadvertently to bomb the huge American base at Da Nang.
    Most important of all, Task Force Alpha was not confronting a fixed target that would faithfully behave as predicted but a living enemy skilled in camouflage and deception that could watch, think, and adapt. Even before the arrival of Task Force Alpha, large sections of the trails system led nowhere, decoys that were purposely put in place to confuse American reconnaissance planes. Fake bridges were erected to draw attack, while real ones, resting on inflated inner tubes, lay invisibly submerged during the day. Back in Santa Barbara, the Jasons had entertained the possibility that the enemy might eventually adopt countermeasures of some kind against the sensors, though they were confident that this would take “some period of time.”
    It took the Vietnamese a week.
    General Dong Si Nguyen, a veteran revolutionary and transportation genius who commanded the entire Ho Chi Minh Trail for most of the war, later reminisced how “the devices were dropped over an area as large as 100 kilometers covering our transportation network. We spent seven days trying to arrive at a solution. We brought vehicles to the area and ran them back and forth throughout the day (to make listeners believe the area was active) … While we distracted the Americans in this manner, the actual convoys were then able to safely move by means of a different route.”
    Specialized teams were meanwhile set up in every section of the trail to hunt for sensors. “They were hard to find,” one hunter said later. “Sometimes they were in an area that was not really important to us, so we deliberately triggered them.” Otherwise, the Vietnamese ran herds of cattle down the trail to simulate troop columns to fool infrared cameras or bottles of human and animal urine to confuse the sniffer-sensors.
    The electronic barrier cost almost $2 billion to set up and roughly $1 billion a year to operate. The funds for the secret operation were so artfully hidden in the defense budget that for years Congress had almost no knowledge or oversight of the operation for which it was voting huge sums of money. There was therefore little official incentive to undercount the amount of damage being inflicted on the enemy. To calculate enemy losses without sending men to look for themselves, deemed an impossibly dangerous task, the air force simply multiplied the number of bombs dropped by the number of people who could in theory be killed by varying types of bomb, such as the SADEYE. The tally produced by this arithmetic—20,723 for Igloo White’s first season—conveyed an air of precision that had little basis in reality. “This process,” an official U.S. Air Force historian tartly noted some years later, was “based on so many assumptions that the end product represented an exercise in metaphysics rather than mathematics.”
    Truck kills were assessed by similarly esoteric methods, even though year after year the Vietnamese still seemed to have the necessary number of trucks on hand to supply their armies in the South. Partisans of the electronic fence explained this away by suggesting that North Vietnam simply replaced lost trucks with imports from Russia and other communist allies. As the same air force historian pointed out, “estimates of North Vietnamese truck imports tended to keep pace with the claims of trucks killed and disabled.”
    Finally, in April 1972, the North Vietnamese launched a devastating offensive using hundreds of tanks and thousands of trucks that had passed down the trail completely unnoticed. When General Lucius Clay, commander of the Pacific Air Force, asked how this mass of vehicles and weapons had totally escaped Igloo White scrutiny, he was told that the matériel must have come by routes “we don’t know about.” In fact, for much of the war, the North Vietnamese had moved a considerable portion of their supplies by sea via the Cambodian port of