In The Line, Scott Van Wynsberghe outlines the history of balloons in wartime and (as many are now aware from recent events) in peacetime:

China’s balloon spying is shocking on so many levels that you can take your pick. There is the ultra-flagrant violation of foreign sovereignty, the stunningly surreal air of denial exhibited by Beijing, and the fearful sense that something in the world order just lurched. There is also puzzlement: what, balloon spying is still a thing? Indeed it is, and its centuries-long history is instructive as to what China is now doing. It also makes clear that the U.S. is no innocent victim here but rather a past offender with a cleaned-up act.

Among the first major studies of aerial reconnaissance was a book brought out by military author Glenn B. Infield way back in 1970. In a way, Infield was charting unknown territory. When he addressed balloons in particular, he traced their use in spying to the many wars associated with the French Revolutionary and Napoleonic eras. In 1794, he related, the French military officer Jean-Marie-Joseph Countelle made an ascent at the city of Maubeuge in order to monitor enemy forces in the area. In the process, Countelle became the first balloon spy.

As technology improved, other firsts followed. By the 1850s, cameras were mounted on French military balloons. In the 1860s, during the American Civil War, Union forces battling the Confederacy used balloons trailing telegraphic wires, which transmitted immediate updates from the balloonists. Yet technology cut both ways. By the early 1900s, balloons had a nemesis in sight, in the form of winged and powered aircraft.

The inevitable showdown occurred in the First World War, and it was ugly. Large numbers of observation balloons were used by all sides in the conflict, and WWI historian Denis Winter claims the Germans alone deployed 170 of them in France by 1917. Typically, such balloons were tethered in place near the frontline, floating at several thousand feet, with telephone wires dangling to the ground. Although they seemed vulnerable, they were actually protected from below by anti-aircraft units, which blasted at any enemy plane that got too close. However, the reverse was also true, with balloons themselves being fired at from the ground. By 1915, says aviation writer Ralph Barker, the British were losing at least a dozen balloons a month from all forms of enemy action. Those balloonists who were not shot to pieces often had to bail out, putting their faith in parachutes that did not always work. (Horrified onlookers called them “balloonatics.”) The fighter pilots responsible for much of this mayhem — which they called “balloon-busting” — may not have had an easy time, but some of them scored heavily, with one Frenchman named Coiffard tallying 28 balloons. Although observation balloons managed to make it to the end of the war, it was a near-run thing. According to author Linda Hervieux, nobody after the war was talking about repeating that experience in any future fighting.

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Once the Second World War was underway, some propaganda leafleting did occur, but secret balloon activity seemed to be at a low level. That was very misleading, because one of the tensest moments in ballooning history was playing out in the background, but it occurred amid so much security that the entire tale took years to emerge. In 1944, Japan launched the first of over 9,000 bomb-rigged balloons​ across the Pacific. Robert C. Mikesh, in a comprehensive 1973 monograph issued by the Smithsonian Institution, noted that almost a thousand of the balloons may have reached North America, but the true number is unknowable, because so many came down in remote wilderness. (One was found by forestry workers in British Columbia as late as 2014.) Mikesh tabulated 285 known incidents, ranging from Alaska all the way south to Baja California and as far inland as Manitoba. Both the U.S. and Canada clamped down hard on any news about the balloons, for fear of providing Tokyo valuable feedback about the results of the campaign. (In other words, balloon counterintelligence became a priority.) In general, the balloons did not cause a lot of harm, but one of them slaughtered six people in Oregon in 1945. By a strange fluke, one of the few groups in the U.S. that knew the full story of the balloons was an element of the Black community. The all-Black 555th Parachute Infantry Battalion was sent to the U.S. West to handle emergencies caused by the balloons.

The remains of a Japanese balloon bomb found in the Monashee Mountains near Lumby, BC in 2014. It was detonated on-site by the bomb disposal unit of Maritime Forces Pacific of the Royal Canadian Navy.

There is a strong temptation to blame the Japanese balloon bombs for what happened next, because the U.S. unaccountably entered the Cold War as the most pugnacious exponent of clandestine ballooning up to that time. Whatever the explanation, the epic struggle between the United States and the Union of Soviet Socialist Republics plunged U.S. ballooning into a tangle of psychological warfare, shadowy science, under-the-table finances, and clandestine belligerence indistinguishable from military attacks. Plus, UFOs and breakfast foods were involved (seriously).