People have been trying to defend against hail since time immemorial. In the Middle Ages there were numerous processions. In the 18th century special cannons were used. The clouds were shot at with a mixture of soot.

In the 1940s, the chemists Irving Langmuir, Vincent Schaefer and Bernard Vonnegut discovered silver iodide as a defense agent. Laboratory tests have produced positive results. People started using rockets to bombard the clouds. The new technology spread very quickly in the West. It was not used in the Soviet Union until the 1960s and from there it spread to the Eastern bloc.

The rockets were later replaced by airplanes. A so-called hail plane can hit the hail cloud better.

The hail protection provided by hail defense is often criticized, however. Critics claim that silver iodide has no effect on hail. Numerous studies have therefore been carried out. Dr. Pachatz studied and recorded hail defense in detail in his doctoral thesis. He could confirm in the laboratory that silver iodide has an effect on the hailstones. Silver iodide dissolves hailstones or makes them smaller. In practice, however, an unexpected problem has arisen. We currently have no measuring device with which we could measure the hailstones in the clouds. Radar can show a hail cloud, but it cannot detect hailstones. We cannot therefore scientifically assess the use of silver iodide.

Source

Günther C. Pachatz, Analyse der Effizienz der Hagelabwehr in der Steiermark anhand von Fallbeispielen, Doctorthesis, University Wien, 2005.
Kurt Werth, Geschichte der Hagelabwehr: Raketen, Kanonen, Wetterläuten, Wolkenimpfung, Versicherung und Netze zum Schutz gegen den Hagel, Retina, 2021.