In early 1942 the United States was still reeling from the Attack on Pearl Harbor. They'd declared war upon the Empire of Japan, but had thus far fought unsuccessfully in every engagement. The West Coast was wary, and prepared for a seemingly inevitable invasion. Cities from Seattle to San Diego had invasion plans including things from air-raid sirens to blackout procedures. Nerves were drawn taut, and there was no shortage of false alarms.
On the night of 24 February 1942 the Air Raid sirens sounded, and the Coast Guard Anti-aircraft guns were ordered to "green alert," putting them in readiness to fire. From the time the battle began until it ended in the early hours of the morning, thousands of people had witnessed the search lights around Los Angeles fix on a target hovering above the city, and anti-aircraft rounds detonate in the sky. Reputable news agencies reported the attack, complete with eye-witness accounts. But the Japanese claim that they never attacked, and there was no wreckage to indicate that anyone actually did. These conflicting accounts cast uncertainty on the nature of the unidentified aircraft that caused the Battle of Los Angeles.
The first sightings of the incoming aircraft came from the Coast Guard shortly after 11:00 PM. Because commercial and private aircraft were fairly common, the Civil Defense Service reacted cautiously to the initial sighting. As reports of the incoming plane--or sometimes fleet--continued and progressed nearer to land, artillery posts were put on alert. By the time they started getting reports of an overhead object from people inland, things were put into action, and the Air Raid Wardens were called in to put the city into blackout. Thousands of volunteer Air Raid Wardens began calling the homes of people in their areas, and ordering them to douse the lights; in so doing they incited people to go out and seek the object that was crawling slowly through the sky.
Some witness accounts describe the interloper above the city as a tremendous single object, while others stated that it was a dispersed group of smaller objects. Many people reported to the papers that they were certain they'd seen US planes approach the object before the shelling began, however the army reported that 4th Interceptor Command was only on alert, and no planes were ever launched. Spotlights lit the skies and illuminated an object moving slowly--sometimes hovering.
At 3:16 AM the 37th Coast Guard Artillery Brigade opened fire while the target was over Culver City. With the city lights all snuffed for the blackout, the barrage of AA shells was the center of attention. The firing continued intermittently through the night until the blackout lifted at 7:21 AM.
The morning papers were filled with details of the incident. Some reported that two Japanese airplanes had been shot down, but such wreckage was never found. Some buildings had been damaged by shells, and there were six casualties-- all of them were on the ground. There were three killed by friendly fire and three more of stress induced by the attack. The Los Angeles Times ran a front page picture depicting the object caught in the search lights; it is uncertain if this picture is an actual photograph or an artist's depiction because of the lack of clarity, i.e. the fact the search lights terminate on the object rather than cast streams past.
The Secretary of the Navy, Frank Knox, immediately denounced accounts of the affair, calling it a false alarm brought about by "war nerves". Since the battle many have proposed that the mysterious object that was seen moving over Santa Monica to Long Beach was a weather balloon, or perhaps an early Japanese Fire Balloon. However to suggest that the Coast Guard commenced firing at a balloon for over an hour implies a degree of incompetence, to say the least.
There are others who have a less pedestrian explanation for that night: that it was a mass Close Encounter of the First Kind. Some stories have circulated that two downed aircraft were found: one in the sea, and one in the San Bernardino mountains, and that they were of obvious extra-terrestrial origin.
The variation in personal accounts contribute little to the solving of this mystery. Some saw one large object in the sky, some saw many smaller objects. Reports on the object's altitude ranged significantly. However, it seems certain that there was something in the sky that night because despite the disparity in the reports, the fact that there were tens of thousands of witnesses make the existence of the object over LA that night impossible to dismiss.