For Reverend Archie Mitchell, the spring of 1945 was a season of change. Not only were the minister and his wife, Elsie, expecting their first child, but he had also accepted a new post as pastor of the Christian and Missionary Alliance Church in the sleepy logging town of Bly, Oregon. Seeking to deepen their newly planted roots, the Mitchells invited five children from their Sunday school class—all between the ages of 11 and 14—on a picnic amid the bubbling brooks and ponderosa pines of nearby Gearhart Mountain on the beautiful spring day of May 5, 1945.

After lumbering up a one-lane gravel road, Mitchell parked his sedan and began to unload picnic baskets and fishing rods as Elsie, five months pregnant, and the children explored a knoll sloping down to a nearby creek. When 13-year-old Joan Patzke spied a strange white canvas on the forest floor, the curious girl summoned the rest of the group. “Look what we found,”

Elsie called to her husband back at the car. “It looks like some kind of balloon.” The pastor glanced over at the group gathered in a tight circle around the oddity 50 yards away. As one of the children reached down to touch it, the minister began to shout a warning but never had a chance to finish.

A huge explosion rocked the placid mountainside. Elsie, the unborn baby and the five children were killed almost instantly by the blast. When a forest ranger in the vicinity came upon the scene, he found the victims radiating out like spokes around a smoldering crater and the 26-year-old minister beating his wife’s burning dress with his bare hands.

What U.S. military investigators sent to the blast scene immediately knew—but didn’t want anyone else to know—was that the strange contraption was a high-altitude balloon bomb launched by Japan to attack North America. After American aircraft bombed Tokyo and other Japanese cities during the Doolittle Raid of 1942, the Japanese military command wanted to retaliate in kind but its manned aircraft were incapable of reaching the West Coast of the United States. What the Japanese military lacked in technology, however, it made up for in geography.

Since the 13th century when a pair of cyclones foiled the fleets of Kublai Khan’s Mongol invaders, the Japanese had long believed that the gods had dispatched “divine winds,” called “kamikaze,” to protect them. During World War II, the military thought the winds could save them once again since its scientists had discovered that a westerly river of air 30,000 feet high—known now as the “jet stream”—could transport hydrogen-filled balloons to North America in three to four days.

For two years the military produced thousands of balloons with skins of lightweight, but durable, paper made from mulberry wood that was stitched together by conscripted schoolgirls oblivious to their sinister purposes. Using 40-foot-long ropes attached to the balloons, the military mounted incendiary devices and 30-pound high-explosive bombs rigged to drop over North America and spark massive forest fires that would instill panic and divert resources from the war effort.

Between November 1944 and April 1945, the Japanese military launched more than 9,000 of the pilotless weapons in an operation codenamed “Fu-Go.” Most of the balloons fell harmlessly into the Pacific Ocean, but more than 300 of the low-tech white orbs made the 5,000-mile crossing and were spotted fluttering in the skies over the western United States and Canada—from Holy Cross, Alaska, to Nogales, Arizona, and even as far east as Grand Rapids, Michigan.

In March 1945, one balloon even hit a high-tension power line and caused a temporary blackout at the Hanford, Washington, plant that was producing plutonium that would be used in the atomic bomb dropped on Nagasaki five months later. None of the balloons, however, had caused any injuries—until Mitchell’s church group came across the wreckage of one on Gearhart Mountain.

Citing the need to prevent panic and avoid giving the enemy location information that could allow them to hone their targeting, the U.S. military censored reports about the Japanese balloon bombs. Although many Bly locals knew the truth, they reluctantly followed military directives and adopted a code of silence about the tragedy as the media reported that the victims died in “an explosion of undetermined origin.”

By the end of May 1945, however, the military decided in the interest of public safety to reveal the true cause of the explosion and warn Americans to beware of any strange white balloons they might encounter—information divulged a month too late for the victims in Oregon.

Ultimately, Fu-Go was a military failure. Few balloons reached their targets, and the jet stream winds were only powerful enough in wintertime when snowy and damp conditions in North American forests precluded the ignition of large fires. The only casualties they caused were the deaths of five innocent children and a pregnant woman, the first and only fatalities in the continental United States due to enemy action in World War II.

The balloon bombs, however, presaged the future of warfare. In his book Fu-Go: The Curious History of Japan’s Balloon Bomb Attack on America, author Ross Coen called the weapon “the world’s first intercontinental ballistic missile,” and the silent delivery of death from pilotless balloons has been referred to as World War II’s version of drone warfare.