“One of the assistants who lived in Leonardo’s household at the time was a technician and locksmith named Giulio Tedesco, known as Jules the German, who returned to Germany around 1499 and spread Leonardo’s idea there. The wheellock came into use in Italy and Germany around that time and proved to be influential in facilitating both warfare and the personal use of guns.18.”

“One of the assistants who lived in Leonardo’s household at the time was a technician and locksmith named Giulio Tedesco, known as Jules the German, who returned to Germany around 1499 and spread Leonardo’s idea there. The wheellock came into use in Italy and Germany around that time and proved to be influential in facilitating both warfare and the personal use of guns.18.”

— Walter Isaacson