Just after 3 a.m. on Feb. 25, 1942, the skies over Santa Monica, California shook to the thunder of an anti-aircraft barrage.

At six minutes after the hour, four batteries of the 37^th Coastal Artillery Brigade opened fire on what spotters believed were enemy aircraft.

Only three months earlier, the Japanese had struck the American naval base at Pearly Harbor. The population along the U.S. west coast feared they’d soon be in the enemy’s bombsights sights too. Could this be the attack Californians were dreading?

Earlier that evening, the gunners had noted a strange red light in the distance, possibly a signal flare presumably lit to guide enemy planes in to the darkened shoreline.

Then shortly after 2:30 a.m., lookouts 30 miles to the south at Long Beach radioed in a sighting of more than two-dozen aircraft heading inland towards the city of Los Angeles at an altitude of 12,000 feet. Minutes before that, radar crews were tracking an unknown object, or group of objects, more than 100 miles out over the Pacific. The operators followed the signal as it moved towards the mainland and then vanished.

The reports were dutifully passed along to the Western Defense Command, which within minutes ordered a total blackout for L.A. All anti-aircraft batteries were brought to alert and air raid wardens fanned out across the city to enforce the ban on lights. Meanwhile, 60 miles inland, pilots of the 4^th Interceptor Command at March Field, were briefed while crews readied their planes.

To the commanders on the ground, the evidence seemed all too clear: California was moments away from being struck by the Japanese.

As the gunners at Santa Monica opened fire at 3:06, their bursts were answered by gun emplacements farther inland. Soon more batteries joined in. For the next hour, the airspace over greater L.A. filled with the flashes and reports of more than 1,400 artillery shells. Air raid sirens pealed adding to the din, while searchlights swept the skies, their crews desperate to illuminate a formation of enemy bombers. City residents scrambled from their beds amid the cacophony; some seeking shelter from the maelstrom, others racing to their roofs to watch the excitement. At least one civilian died of panic-induced heart failure; as many as four others were killed in traffic accidents.

As the battle raged, reports (some of them quite hysterical) filtered in to the commanders. “Swarms” of planes had been spotted, said some observers; “several hundred” were overhead reported others. A number of eyewitnesses claimed that as many as four enemy aircraft had been blasted from the skies by the withering barrage — one had reportedly even slammed into a Hollywood street. Frustratingly, none of these reports could be verified.

Amid the torrent of chatter, little if any mention was made of bomb damage from the raiders. As far as commanders could determine, no targets had been struck — no ports, rail facilities, airfields or factories were ablaze.

After several deafening minutes, the tempo of fire tapered off. By 4:15 a.m., the all clear was sounded and an erie calm descended onto the city. There were no signs of any Japanese aircraft. By sunrise the alert had been suspended. What became known as the Battle of Los Angeles was over.

The following day, the press and the rattled citizenry of Southern California searched for an explanation for the mysterious incident; the military scrambled to provide one.

Frank Knox, Secretary of the Navy, flatly denied that any enemy aircraft had been detected. He called the entire incident a “false alarm”.

The army declared that most sightings were either based on hearsay or exaggerations, although in spite of the navy’s announcement, it wouldn’t rule out the possibility that at least one enemy aircraft could have penetrated California airspace.

Even the War Department speculated that Japanese planes might have been spotted over L.A. and if so they would have had to have been launched from enemy subs or even flown from secret airfields in Mexico or the California desert.

Reporters on scene, including none other than war correspondent Ernie Pyle himself, claimed to have seen a lot of fireworks that night, but no Japanese planes.

Soon major daily newspapers were chalking the entire affair up to incompetence and jitters on the part of gun crews, air spotters and controllers. But to be fair, such anxiety was hardly unjustified. Only two days earlier, a Japanese submarine had surfaced off Ellwood, Calif., nearly 100 miles up the coast from L.A., and fired a dozen shells at an oil refinery causing light damage. Were local defences simply on a hair trigger after the recent bombardment?

Perhaps, but the lack of a definitive official explanation about the L.A. Incident spawned all manner of speculation.

Some surmised that the pre-dawn conflagration was touched off by nervous crews who had spotted a commercial flight.

One California congressman, Leland Ford, reportedly wondered aloud if the entire affair had simply been staged so as to facilitate the relocation of vital war production plants farther inland.

In subsequent years even more outlandish theories were posited.

UFO enthusiasts and conspiracy theorists alike have long maintained that coastal defences had actually unleashed a barrage on extraterrestrial visitors and that Washington had quickly moved in to suppress the whole story to stave off panic.

Yet, judging by the mass-hysteria that followed the 9/11 attacks, it was probably a mix of darkness, fatigue, frayed nerves and paranoia all brought to a head by something entirely mundane… like a stray weather balloon. At least that’s the conclusion of an official U.S. Air Force history of the incident written 40 years later.

“A careful study of the evidence suggests that meteorological balloons—known to have been released over Los Angeles—may well have caused the initial alarm,” wrote the authors of a 1983 military report on the Battle of Los Angeles.

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Comedy of Errors
The Battle of Los Angeles served as the backdrop to the little known Robert Zemeckis, Steven Spielberg comedy 1941. Set in the days the following the attack on Pearl Harbor, the film shows how panicky civilians and gung-ho soldiers unwittingly unleash bedlam into the streets of the L.A. amid mounting fears that the Japanese are poised to strike the city at any moment. Little do the characters realize, a real Japanese submarine is in fact cruising the waters off the coast looking for something (or rather anything) to attack. Despite the all-star cast and the state of the art special effects, 1941 did poorly at the box office. The complete film (with commercials) is available here on YouTube.