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 sensational reports and speculations of a cover-up. A small number of 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. This event inspired the film Battle: Los Angeles.
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 a.m. 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 a.m. The "all clear" was sounded and the blackout order lifted at 7:21 a.m.
In addition to several buildings damaged by friendly fire, three 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: "The Battle of Los Angeles" During the night of 24/25 February 1942, unidentified objects caused a succession of alerts in southern California. On the 24th, a warning issued by naval intelligence indicated that an attack could be expected within the next ten hours. That evening a large number of flares and blinking lights were reported from the vicinity of defense plants. An alert called at 1918 [7:18 p.m., Pacific time] was lifted at 2223, and the tension temporarily relaxed. But early in the morning of the 25th renewed activity began. Radars picked up an unidentified target 120 miles west of Los Angeles. Antiaircraft batteries were alerted at 0215 and were put on Green Alert—ready to fire—a few minutes later. The AAF kept its pursuit planes on the ground, preferring to await indications of the scale and direction of any attack before committing its limited fighter force. Radars tracked the approaching target to within a few miles of the coast, and at 0221 the regional controller ordered a blackout. Thereafter the information center was flooded with reports of "enemy planes, " even though the mysterious object tracked in from sea seems to have vanished. At 0243, planes were reported near Long Beach, and a few minutes later a coast artillery colonel spotted "about 25 planes at 12,000 feet" over Los Angeles. At 0306 a balloon carrying a red flare was seen over Santa Monica and four batteries of anti-aircraft artillery opened fire, whereupon "the air over Los Angeles erupted like a volcano." From this point on reports were hopelessly at variance. Probably much of the confusion came from the fact that anti-aircraft shell bursts, caught by the searchlights, were themselves mistaken for enemy planes. In any case, the next three hours produced some of the most imaginative reporting of the war: "swarms" of planes (or, sometimes, balloons) of all possible sizes, numbering from one to several hundred, traveling at altitudes which ranged from a few thousand feet to more than 20,000 and flying at speeds which were said to have varied from "very slow" to over 200 miles per hour, were observed to parade across the skies. These mysterious forces dropped no bombs and, despite the fact that 1,440 rounds of anti-aircraft ammunition were directed against them, suffered no losses. There were reports, to be sure, that four enemy planes had been shot down, and one was supposed to have landed in flames at a Hollywood intersection. Residents in a forty-mile arc along the coast watched from hills or rooftops as the play of guns and searchlights provided the first real drama of the war for citizens of the mainland. The dawn, which ended the shooting and the fantasy, also proved that the only damage which resulted to the city was such as had been caused by the excitement (there was at least one death from heart failure), by traffic accidents in the blacked-out streets, or by shell fragments from the artillery barrage. Attempts to arrive at an explanation of the incident quickly became as involved and mysterious as the "battle" itself. The Navy immediately insisted that there was no evidence of the presence of enemy planes, and [Secretary of the Navy], Frank Knox announced at a press conference on 25 February that the raid was just a false alarm. At the same conference he admitted that attacks were always possible and indicated that vital industries located along the coast ought to be moved inland. The Army had a hard time making up its mind on the cause of the alert. A report to Washington, made by the Western Defense Command shortly after the raid had ended, indicated that the credibility of reports of an attack had begun to be shaken before the blackout was lifted. This message predicted that developments would prove "that most previous reports had been greatly exaggerated." The Fourth Air Force had indicated its belief that there were no planes over Los Angeles. But the Army did not publish these initial conclusions. Instead, it waited a day, until after a thorough examination of witnesses had been finished. On the basis of these hearings, local commanders altered their verdict and indicated a belief that from one to five unidentified airplanes had been over Los Angeles. Secretary Stimson announced this conclusion as the War Department version of the incident, and he advanced two theories to account for the mysterious craft: either they were commercial planes operated by an enemy from secret fields in California or Mexico, or they were light planes launched from Japanese submarines. In either case, the enemy’s purpose must have been to locate anti-aircraft defenses in the area or to deliver a blow at civilian morale. The divergence of views between the War and Navy departments, and the unsatisfying conjectures advanced by the Army to explain the affair, touched off a vigorous public discussion. The Los Angeles Times, in a first-page editorial on 26 February, announced that "the considerable public excitement and confusion" caused by the alert, as well as its "spectacular official accompaniments," demanded a careful explanation. Fears were expressed lest a few phony raids undermine the confidence of civilian volunteers in the aircraft warning service. In Congress, Representative Leland Ford wanted to know whether the incident was "a practice raid, or a raid to throw a scare into 2,000,000 people, or a mistaken identity raid, or a raid to take away Southern California’s war industries." Wendell Willkie, speaking in Los Angeles on 26 February, assured Californians on the basis of his experiences in England that when a real air raid began "you won’t have to argue about it—you’ll just know." He conceded that military authorities had been correct in calling a precautionary alert but deplored the lack of agreement between the Army and Navy. A strong editorial in the Washington Post on 27 February called the handling of the Los Angeles episode a "recipe for jitters," and censured the military authorities for what it called "stubborn silence" in the face of widespread uncertainty. The editorial suggested that the Army’s theory that commercial planes might have caused the alert "explains everything except where the planes came from, whither they were going, and why no American planes were sent in pursuit of them." The New York Times on 28 February expressed a belief that the more the incident was studied, the more incredible it became: "If the batteries were firing on nothing at all, as Secretary Knox implies, it is a sign of expensive incompetence and jitters. If the batteries were firing on real planes, some of them as low as 9,000 feet, as Secretary Stimson declares, why were they completely ineffective? Why did no American planes go up to engage them, or even to identify them?... What would have happened if this had been a real air raid?" These questions were appropriate, but for the War Department to have answered them in full frankness would have involved an even more complete revelation of the weakness of our air defenses. At the end of the war, the Japanese stated that they did not send planes over the area at the time of this alert, although submarine-launched aircraft were subsequently used over Seattle. 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. This theory is supported by the fact that anti-aircraft artillery units were officially criticized for having wasted ammunition on targets which moved too slowly to have been airplanes. After the firing started, careful observation was difficult because of drifting smoke from shell bursts. The acting commander of the anti-aircraft artillery brigade in the area testified that he had first been convinced that he had seen fifteen planes in the air, but had quickly decided that he was seeing smoke. Competent correspondents like Ernie Pyle and Bill Henry witnessed the shooting and wrote that they were never able to make out an airplane. It is hard to see, in any event, what enemy purpose would have been served by an attack in which no bombs were dropped, unless perhaps, as Mr. Stimson suggested, the purpose had been reconnaissance.
– The Army Air Forces in World War II, prepared under the editorship of Wesley Frank Craven, James Lea Cate. v.1, pp. 277-286, Washington, D.C. : Office of Air Force History : For sale by the Supt. of Docs., U.S. G.P.O., 1983
Every February, the Fort MacArthur Museum, located at the entrance to Los Angeles Harbor, hosts an entertainment event called "The Great LA Air Raid of 1942."