In Images at War, the historian Michèle Martin mentions the difficulties the Prussians had in stopping French messengers/ spies from escaping sieges using balloons during the Franco-Prussian War. She mentions that the French newspaper Le Monde Illustré ran a story alleging that the Prussians devoted a cavalry unit to pursuing balloons to intercept them where they landed, given their failure to reliably shoot them down. However, Martin does not go into detail on whether or not this claim is substantiated. At first glance it appears a little farcical, do we know if this is propaganda or a real tactic they considered?
The article cited by Michèle Martin is this one, dated from 22 October 1870. Author Pierre Véron claimed that the Prussians had "installed units of flying cavalry responsible for pursuing the balloons as far as they could see them." It's a single line in the article, and it seems to be derived from a equally short bit of news printed in the French newspapers since the 17 October, which was itself a translation from a dispatch by the Times correspondent sent from Berlin on 8 October that went like this:
Balloons are daily sent off from Paris, and are carried by the prevailing easterly winds to the provinces which are unoccupied by the Germans. They are followed by light cavalry as long as they continue in sight.
The line by Véron about the Prussians having put special cavalry units in place to chase the balloons seems to be a slight exaggeration, made to push his point that the Prussians were desperate to capture the balloons, and that it was necessary to enforce operational security, and if possible to send the balloons at night (which was eventually done).
Note that when the Times dispatch was written on 8 October, only 7 balloons had been sent. We do have a direct testimony about a close encounter with the Prussian calvalry, told by aeronaut Gaston Tissandier, who flew the Céleste on 30 September 1870 (it was the fourth flight).
Departing from the gas factory of Vaugirard at 9-10 am, Tissandier was flying westward, reaching 1800 m. When he was above the palace of Versailles, he saw German officers below looking at him with spyglasses. He dumped a packet of 1000 anti-German propaganda flyers (the proclamations) on them, and flew over a German camp, where he was shot at (he dumped another packet of flyers). Over the Hourdan forest, his balloon started leaking gas:
I quickly grab a ballast bag and empty it overboard, but my barometer tells me that I am still descending; the cold penetrates me to the bones. The balloon quickly reaches altitudes of 1000 metres, 800 metres, 600 metres. It descends again. I successively empty three bags of ballast to keep my balloon at only 500 metres above the forest, because it refuses to go any higher.
At this moment, I hover over a crossroads. A group of men is gathered there. Great God! they are Prussians. Here are others; uhlans, cavalrymen are riding along the paths. I have only a bag of ballast left. I launch my last packet of proclamations into space. But the balloon has lost a lot of gas, through solar dilation and through its leaks; it is cooled, its ascensional force is singularly diminished.
I am only 420 metres high, a bullet could well hit me.
Fortunately for me the wind is strong; I fly like an arrow over the trees; the uhlans look at me astonished, and see me pass without any rifle shot threatening me. I continue my route above green meadows, gracefully framed by hawthorn hedges.
Tissandier landed safely in Dreux at about 11-12 am.
As the balloons flew too high to be shot down by rifles, unless they lost altitude by accident as almost had happened to Tissandier, the Prussians developed the first anti-aircraft weapon, Krupp's Ballonabwehrkanone or BaK (shown here in Tissandier's book), a 37-millimeter breech-loading cannon mounted to the bed of a carriage (so it was also the first "technical", more than a century before the Toyota Hilux!). According to Tissandier, this mousquet à ballons was installed in Versailles, where it was paraded "triumphantly" in the streets. As soon as spotters saw a ballon rising above Paris, the news was transmitted by telegraph to Versailles and the horse-drawn gun was moved as fast as possible to a position where an experienced artilleryman could try to shoot the balloon. Tissandier says that many French aeronauts heard projectiles whizzing by at altitudes as high as 800 to 1000 m. The Daguerre was brought down and captured by a Prussian cavalry unit on 12 November 1870, though the French Army later believed that it was shot by rifles, not by the mousquet à ballons (Dufaux, 1886). In any case, German attempts to shoot the balloons out of the sky were not very successful, and did not prevent the transmission of several millions of messages from and to Paris. Out of the 64-67 balloons that left Paris during the war, only 5 were downed and captured by the Prussians. So: even if the Prussians did not have special cavalry units to capture balloons, they invented anti-aircraft warfare to shoot them.
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