Foo Fighters reportedly pursued aircraft during World War II. They were described as small, fast moving balls or disks of light that would surround the plane. Some pilots believed them to be enemy inventions sent to distract them from their mission.

One of the first reports happened in October 1943 when US B-17s were flying over Schweinfurt, Germany. During the bombing run dozens of small, silvery disks suddenly appeared. The disks were about an inch (2.5cm) thick and four inches (10cms) in diameter. One of the aircrew saw one of the disks hit the tail of one of the planes but it had no effect on the aircraft.

A year later over Sumatra a B-29 bomber was followed by a red throbbing sphere. It was constantly on the starboard wing and paced the bomber at 210mph before turning at a right angle and accelerating at high speed in a different direction. There are dozens of reports of the Foo Fighters from Allied, German and Japanese pilots.

Sceptical scientist Donald Menzel believed the fighters were light reflections, but this does not account for the cases where Foo Fighters caused tangible, physical effects on the aircraft. They remain one of the most intriguing UFOs of the 20th Century.