4. Northrop XB-35

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This is another one that probably set off a flurry of UFO reports if it ever wandered out and around in the public airspace. Designed as a heavy bomber for use by the U.S. Army Air Force in the late 1940’s, this weird ancestor of the modern-day B-2 flew numerous test flights before the idea was ultimately scrapped in favor of work to develop a jet-powered version known as the YB-49.