______In 1870 the Franco-Prussian War broke out, changing the balance of power on the European continent. Prussia and its allied German states quickly destroyed or outmanuevered the French armies on the frontier and captured Emperor Napoleon III, ending his "imperial" rule.
______Under normal circumstances this would have ended the war. But a scratch force of militia called the Garde Mobile was raised to replace the defeated armies. This force retreated into Paris. The Germans placed them under siege.
______A means to communicate with the rest of unoccupied France was sought. Carrier pigeons were used to a small degree, but hunting birds employed by the Germans had a meal of many of them. Then the besieged Parisians hit upon using hydrogen balloons. These balloons worked most of the time (one ended up in Norway) and some government officials were even able to escape by such means, most notably Leon Gambetta who organized further resistance with the Provisional Government that initially met at Tours.

______Needless to say, the Prussians were not pleased by this development. They attempted to engage the balloons using small arms and conventional artillery, but rifles could not be aimed accurately at such an angle, even when the balloon was within range, and artillery pieces super-elevated so that they could be brought to bear on aerial targets were also ineffective. So another solution was sought.

______The solution reached was the design of a special gun, one specifically designed to shoot down balloons. This was the ballongeschutz, the balloon gun designed and manufactured by the famous arms company Krupp. The weapon was a wagon-mounted breech-loaded 20mm gun. The gun was attached to a swivel on top of a pedestal, allowing the weapon to be aimed at very high angles. The wagon could be moved rapidly to pursue airborne balloons and continue to engage them.
______This was the world's first anti-aircraft gun. The Krupp gun was primitive and used simple sights similar to any rifle of the day, but it was the beginning of a field in which Krupp would dominate right into World War II. Unfortunately for the Prussians, it never succeeded in shooting down any balloons, although they did force them to continue their flights at night, with much greater risk to the crewmen.