Initially, the target of the aerial barrage was thought to be an attacking force from Japan, but speaking at a press conference shortly afterward, Secretary of the Navy Frank Knox called the incident a "false alarm." Newspapers of the time published a number of reports and speculations of a cover-up. Some modern-day UFOlogists have suggested the targets were extraterrestrial spacecraft. When documenting the incident in 1983, the U.S. Office of Air Force History attributed the event to a case of "war nerves" likely triggered by a lost weather balloon and exacerbated by stray flares and shell bursts from adjoining batteries.
Air raid sirens sounded throughout Los Angeles County on the night of 24-25 February 1942. A total blackout was ordered and thousands of air raid wardens were summoned to their positions. At 3:16 am the 37th Coast Artillery Brigade began firing 12.8-pound anti-aircraft shells into the air at reported aircraft; over 1,400 shells would eventually be fired. Pilots of the 4th Interceptor Command were alerted but their aircraft remained grounded. The artillery fire continued sporadically until 4:14 am The "all clear" was sounded and the blackout order lifted at 7:21 am.
In addition to several buildings damaged by friendly fire, four to five civilians were killed by the anti-aircraft fire, and another three died of heart attacks attributed to the stress of the hour-long bombardment. The incident was front-page news along the U.S. Pacific coast, and earned some mass media coverage throughout the nation.
Within hours of the end of the air raid, Secretary of the Navy Frank Knox held a press conference, saying the entire incident was a false alarm due to anxiety and "war nerves". Knox's comments were followed by statements from the Army the next day that reflected General George C. Marshall's belief that the incident might have been caused by commercial airplanes used as a psychological warfare campaign to generate panic. Some contemporary press outlets suspected a cover up. An editorial in the "Long Beach Independent" wrote, "There is a mysterious reticence about the whole affair and it appears that some form of censorship is trying to halt discussion on the matter." Speculation was rampant as to invading airplanes and their bases. Theories included a secret base in northern Mexico as well as Japanese submarines stationed offshore with the capability of carrying planes. Others speculated that the incident was either staged or exaggerated to give coastal defense industries an excuse to move further inland. Representative Leland Ford of Santa Monica called for a Congressional investigation, saying, "...none of the explanations so far offered removed the episode from the category of 'complete mystification'... this was either a practice raid, or a raid to throw a scare into 2,000,000 people, or a mistaken identity raid, or a raid to lay a political foundation to take away Southern California's war industries.
In 1983, the Office of Air Force History concluded that an analysis of the evidence points to meteorological balloons as the cause of the initial alarm.
Many witnesses claim to have seen not meteorological balloons, but something else. Some witnesses lived right on the beach and say that the object was so close at one point before the shooting began, that they could reach out and practically touch it. Witnesses even claim that shortly after the incident, a squadron of planes appeared and searched the area over the ocean where it was believed the object that was shot down, landed. Naval ships were also reported in the same area.
Did the military find what it was they shot down? If so, why aren't they saying they did? What did they recover?
UFOligists say that this incident beats Roswell all to hell. Not just because this incident in Los Angeles occurred 4 years before Roswell, but for the fact that millions of people saw this lighted object and described it as moving intelligently on its own through the night skies.
But like Roswell, the military insists on covering this incident up. Meanwhile, those who were there know that they witnessed more than just a "Battle of Los Angeles" - they witnessed a real life "War of the Worlds".
In later investigations, it was shown that there were meteorological balloons in the area, however, experts have since come out and said that those balloons would have been to high up in the atmosphere for to be seen with the naked eye at night. Not to mention that after the shellacking that the military unleashed upon it, it would have been in complete shreds and floating on the ocean waters or washed ashore onto the sand in the early morning tide. No debris ever washed ashore.
So the speculation persists. Those who were there, including military officials, will tell you that something was flying in the skies that night. Officially, however, the military personnel will tell you it was a weather balloon. That same story (excuse) came in handy four years later at Roswell.
Source: Wikipedia