This patent covers a design that became the first Durex derailleur model. It was essentially a chain tensioning arm that could be shifted by hand. Note the lack of control cable. I believe that it really made it into production - there are convincing photos of it.

• Publisher: Deutsches Patent- und Markenamt
• Inventor: Erich Lucas
• Country: Germany
• Date: Priority date September 1932
• Derailleur brands: Durex
• Derailleurs: Durex