The Battle of Los Angeles took place on the night of 24 February 1942. It was more of a 'battle' than a battle: only one side did any shooting, and it's not at all clear that there was a second side. The defenders of Los Angeles thought there was: they claimed they were shooting at aircraft of mysterious (but presumed to be Japanese) origin. This is where I come in.
The incident is mainly known now by a photograph showing ... something... trapped in searchlight beams, which appeared in the Los Angeles Times on 26 February 1942. Its authenticity has never been questioned, but it was clearly heavily retouched. Recently, an earlier copy of the photo turned up in the archives of the LA Times. It's definitely been retouched less, if at all. I'm not even going to reproduce the better-known-but-retouched version (which can be seen elsewhere); instead, here's the newly-found-and-less-retouched version:
This photo (or rather its retouched version) has been used to argue that there was in fact ... something... over Los Angeles that night (most likely an extraterrestrial spaceship, obviously). Unlike Kentaro Mori, I do think there is... something... there. But it's not a Zeta Reticulan battlecruiser. It's a cloud.
Firstly, there must be an actual, physical object being illuminated here. Crossed searchlight beams alone wouldn't produce the effect seen here, at least with contemporary photographic technology. The following photo (taken at Bremerton, Washington state, also in 1942) shows this:
The photographic film (or plate) is already saturated due to the brighter beams; and you can't get whiter than white.
Secondly, searchlights shining on clouds do produce irregular shapes of light. Here's another contemporary photo, of searchlights illuminating the base of a cloud deck (again, coincidentally, this was taken in southern California too, roughly contemporaneously):
You can tell it's a cloud deck (or at least a big cloud) because of the way the beams just stop going vertically and diffuse away horizontally a little. All of their light has been absorbed and scattered by the cloud. In the Battle photo, the beams do continue through the object, though much diminished; the object's edges are a bit better defined than in the above photo. Both of these would be consistent with a small cloud. (See here for similar arguments.)
Thirdly, see those little blobs surrounding the object in the Battle photo? They're due to bursting anti-aircraft shells. The question is, are they actual flashes of light from the explosions themselves, or are they the puffs of smoke left behind, showing up because of the lightshow? I think it's mostly the latter, because nearly all appear to be in searchlight beams (though that could be a coincidence of perspective). However, the blobs above the object aren't, and I think that's because they are being illuminated by light being scattered upwards from the cloud. That wouldn't happen if the object were solid: being lit from underneath, it would reflect light down and to the sides, not up. But a small cloud will scatter light in all directions, including up. (But it's possible, too, that the blobs above the object are actual shell explosions: they are noticeably bright, after all.)
So, that's my take on the Battle of Los Angeles photo. But it's worth remembering that the photo only represents one aspect of what happened that night. And the Battle itself came after a series of events which heightened alarm on the West Coast. (The Bremerton photo above may have been taken during one of these scares.) Most obviously, of course, there was the Japanese attack on Pearl Harbor on 7 December 1941. There then followed reports of an aircraft carrier off San Francisco combined with radar tracking of aircraft coming in from the sea (8 December); reports of a group of 34 Japanese warships near Los Angeles (9 December) The next few months were relatively quiet, but the loyalties of ethnic Japanese living on the West Coast were coming under increasing suspicion. Meanwhile, the other side of the country was having scares about German attacks: an air raid alert in New York (9 December) turned out to be a false alarm; but U-boat shellings of oil refineries on Aruba (a Dutch colony, but in America's backyard) were quite real (16 and 19 February 1942). Back in the west, an oil refinery at Ellwood, California, was similarly shelled, this time by a Japanese submarine (23 February). A report by naval intelligence warned that an attack of some kind could be expected on 24 February; reports of 'a large number of flares and blinking lights' were seen near armaments factories that day; and then the Army's radars detected an aircraft 120 miles to the west of Los Angeles, approaching the coast. Air defences were naturally put on the alert; a blackout was put into effect. The official US Air Force history describes what follows:
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.1
Four aircraft were claimed to have been shot down for the 1440 AA shells fired, though no wreckage was found. Several civilians died (from falling shrapnel and/or heart attacks, accounts seem to vary). The next day, the Secretary of the Navy, Frank Knox, said it had all been a false alarm; Henry Stimson, Secretary of War (responsible for air and coastal defence) maintained that up to five aeroplanes had been over Los Angeles. Perhaps they were launched from Japanese submarines; or perhaps Japanese secret agents were flying civilian planes over Los Angeles for some sort of psychological warfare operation. (All of which confirmed the need to intern ethnic Japanese Americans, of course.) But there's no evidence that there were any aircraft (or spacecraft) over Los Angeles that night. It was another mystery aircraft scare, a repeat in pattern if not in detail of the Russian balloon scare half a century before.