The Battle of Los Angeles is one of the earliest alleged UFO sightings that fueled conspiracy theories among Americans.
Eye-witnesses claim they saw a mystery object flying in the sky in February 1942 – just weeks after the Japanese air force attacked Pearl Harbor.
Officials received a warning that mainland Los Angeles could be under siege by Japanese forces over a 10 hour period in 1942.
Officers fired rounds of artillery from .50 caliber machine guns into the sky in anticipation that enemy planes would land.
There were no planes but the incident fueled conspiracies about a potential UFO sighting as some reportedly saw a "mysterious" flying object, according to History.
Army officials tried to say that commercial aircraft "sent by Japan" passed over the LA skyline but the Office of Air Force History debunked the theory in 1983 - adding a weather balloon was launched to help with the winds.
Believers say photos of the bright lights reportedly "prove" the phenomenon was an extraterrestrial craft.
Meanwhile, expert and historian Kathryn Dorsch said she wouldn't describe the incident as a "UFO sighting" or "critical to the history of the UFO debate".
She told The Sun: "I also wouldn't talk about it in the same terms as I would later sightings. The post-1947 UFO is a very particular kind of thing that depends on a confluence of post-WWII anxieties, geopolitical tensions, and social concerns."
In an article for Foreign Policy, Dorsch argues that the “modern UFO” can be traced back to 1947 following the alleged sightings by Kenneth Arnold in the Cascade Mountains near Washington State.
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