Still largely unknown, these armaments were a byproduct of an atmospheric experiment by the Axis power. In the 1940s, the Japanese were mapping out air currents by launching balloons attached with measuring instruments from the western side of Japan and picking them up on the eastern side.

The researchers noticed that a strong air current traveled across the Pacific at about 30,000 feet.

Using that knowledge, in 1944 the Japanese military made what many experts consider the first intercontinental weapon system: explosive devices attached to paper balloons that were buoyed across the ocean by a jet stream.

Experts estimate it took between 30 and 60 hours for a balloon bomb to reach North America's West Coast.

Atmospheric uncertainty made for an uncontrolled attack. "An