Franz Helm

Franz Helm ( – 1567) was an artillery master who lived and worked in what is now Germany in the first half of the 16th century. By his own account, he was born in Cologne, perhaps around 1500. Described as a "shooter, cannonier and fireworker," Helm fought with the armies of the Holy Roman Emperor Charles V against the Ottoman Empire. He subsequently moved to Landshut in the then Duchy of Bavaria, where he served the dukes William IV, Louis X and Albert V. He later served John II, Count Palatine of Simmern.

Works Two of Helm's works have survived to the present day. In the 1520s he wrote a comprehensive description of an 'ideal' armoury which, though it has not survived as a stand-alone work, is found incorporated into some texts of his later surviving work, the Buch von den probierten Künsten ("Book of the practical arts"). This was given in manuscript form to his patron, Duke Albert V, some years before the end of Helm's career. Whether it had any practical influence on the duke's army is unclear but it is possible that the later construction of the royal armoury at Munich's Marstallplatz followed Helm's recommendations. The book follows a format that had become quite traditional by that point, albeit with the inclusion of modern elements. It is organised in the same fashion as the highly influential Feuerwerkbuch of 1420, reproducing many of the earlier book's instructions verbatim. Helm writes in several places that he had drawn on old "art books" in compiling his own book. Although he treats the older material respectfully, he does not shy away from criticising outdated methods – for instance, describing some old-style artillery pieces as curiosities and calling one method of shooting described in the Feuerwerkbuch as "strange" – and provides updated information on modern methods and equipment. In various places, he explicitly calls new artillery methods "novel" and "superior".

Rocket cat

One method described by Helm has attracted attention for its illustration of what has been dubbed a 'rocket cat' The same illustration also shows what appears to be a rocket-propelled dove. The illustration appears in various forms in different manuscript versions of Helm's book, as well as in the 1625 printed edition. The images appear in a section titled "To set fire to a castle or city which you can't get at otherwise," in which Helm describes ways of using incendiary devices strapped to animals to set fortified places on fire.

The concept was until the 18th century circulated. But Helm was not the first to propose or use incendiary animals; the Biblical figure Samson is described as attaching torches to the tails of three hundred foxes, leaving the panicked beasts to run through the fields of the Philistines, burning all in their wake. Early Sanskrit texts, early Scandinavian sources and the Primary Chronicle mention cats and birds bearing incendiary devices, while the 10th century Chinese manual Hu Chhien Ching and its 11th century successor Wu Ching Tsung Yao describe and illustrate a series of "fire animals". These include "apricot-stone fire sparrows" carrying burning tinders attached to their legs inside an apricot stone, with the hope that they would fly into the enemy's granaries and set them on fire, and "magic-fire flying crows", artificial birds powered by four rocket tubes. Most often Chinese or Japanese sources talked about forcing oxen or horses for attacks.