In February 1942, the entire west coast of the United States was on edge.

Only two months before, the Japanese had successfully executed a surprise, devastating attack on Pearl Harbor, thrusting the United States into war. The Imperial Army seemed unstoppable, as Pacific island after Pacific Island fell under Japanese control. Many in California, Oregon, and Washington believed it was only a matter of time before that same army turned its sights on the U.S. mainland. Rumors abounded, causing schools to close, black-out orders to be enacted, and radio silence to be imposed.

These fears were not ungrounded. Secretary of War Henry Stimson warned that American cities should be prepared to accept “occasional blows” from enemy forces. And, for the past few months, Japanese submarines had been patrolling the western seaboard. They had sunk two merchant ships, damaged six others, and engaged in skirmishes with the U.S. Navy. Beach goers kept their eyes on the ocean; the enemy was out there, they knew. And it wouldn’t take long before what seemed like a distant war would land upon their shores.

And land it did on February 23, 1942.

Shortly after seven that evening, residents began to hear what they believed to be thunder. Only it wasn’t thunder. An I-17 Japanese submarine, under the command of Kozo Nishino, had opened fire on the town of Goleta, near Santa Barbara, home to the Ellwood Oil Field, the largest oil field in California. Although aiming their deck gun at the oil storage tanks, many shells missed their targets. The Japanese shells destroyed a derrick and pump house. The Ellwood Pier and catwalk suffered minor damage, while one shell narrowly avoiding hitting nearby Wheeler’s Inn. The entire episode lasted only about twenty minutes before the shelling ceased and the submarine disappeared into the night.

The physical destruction was minor. The psychological damage, however, was meteoric.

The following night, on February 24, the Office of Naval Intelligence (ONI) issued a warning that an attack on mainland California could be expected within the next ten hours. Units on the California coast were put on alert.

Shortly after 2 a.m. the next day, military radar picked up what appeared to be an enemy contact some 120 miles west of Los Angeles. Air raid sirens sounded across Los Angeles county at 2:25 a.m. and a citywide blackout was put into effect. Air wardens were called to their posts and, within minutes, troops had manned anti-aircraft guns and begun sweeping the skies with searchlights. 

At 3:16 am, the 37th Coast Artillery Brigade in Santa Monica began firing .50-caliber machine guns and 12.8-pound anti-aircraft shells into the air at reported aircraft. Before long, many of the city’s other coastal defense weapons had joined in. By the time the “attack” was over an hour later, over 1,400 shells had been fired.

Smoke and searchlights filled the skies. Chaos filled the streets. Conflicting reports poured in from all over the city. Some described Japanese aircraft flying in formation, bombs falling and enemy paratroopers descending to the ground. There was even a claim of a Japanese plane crash landing in the streets of Hollywood. Others, including Coastal Artillery Corps Colonel John G. Murphy later, expressed confusion, as neither he nor those around him saw “no planes of any type in the sky—friendly or enemy.”

The “all clear” was eventually sounded and the blackout order lifted at 7:21 a.m. But, as exhausted and nerve-stricken residents emerged from their homes, they discovered something curious: there appeared to have been no enemy attack. “Although reports were conflicting and every effort is being made to ascertain the facts, it is clear that no bombs were dropped and no planes were shot down,” read a statement from the Army’s Western Defense Command. 

The only damage had come from friendly fire. During the “attack” anti-aircraft shrapnel shattered windows and ripped through buildings in the city. One dud careened into a Long Beach golf course, and several residents had their homes partially destroyed by 3-inch artillery shells. In addition, at least five people died during the night as result of heart attacks or car accidents that occurred during the black-out. Even worse, many Japanese-Americans were arrested for allegedly trying to assist or signal enemy aircraft, a chilling beginning to the paranoia-induced “internment camps” that soon dotted the west coast.

So, if it hadn’t been a Japanese attack, what was it?

Over the next few days, government and media outlets issued contradictory reports on what later became known as the “Battle of Los Angeles.” Secretary of the Navy Frank Knox dismissed the firefight as a false alarm brought on by “jittery nerves.” But what about the claims by the thousands of people who believed they saw something in the skies that night?

Secretary of War Henry Stimson maintained that at least 15 planes had buzzed the city and put forth the idea the phantom fighters might have been commercial aircraft “operated by enemy agents” hoping to strike fear into the public (though he later backtracked on this claim). There were no shortage of conspiracy theories, from UFOs to a government-led exercise to help defense industry complexes achieve their goal of moving further inland.

The most likely explanation, however, is the one put forth by the Office of Air Force History in 1983. On the night of the “attack,” the United States Coast Artillery Association recognized a meteorological balloon that was released around 1:00 a.m. to help determine wind conditions. Itchy trigger fingers and heightened paranoia combined with the lights and silver color on the balloon to create the illusion of enemy aircraft. Once the shooting began, the disorienting combination of searchlights, smoke and anti-aircraft flak might have led gunners to believe they were firing on enemy planes even though none were actually present. 

The irony of the “pretend battle” occurring in Los Angeles was not lost on journalists. In an article from March 1942, the New York Times wrote that as the “world’s preeminent fabricator of make-believe,” Hollywood appeared to have played host to a battle that was “just another illusion.”