Walther Toggle-Locked Semiauto Shotgun (ouch!)
11m
Between the world wars, the Walther company designed and marketed a short recoil, toggle-locked 12 gauge shotgun for sporting use. It was patented by the Walther brothers, but actually manufactured by the Deutsche-Werke consortium, which was organized by the German government to employ German workers and export guns for much-needed foreign hard currency (they also made the Ortgies pistols).
The Walther shotgun was not particularly successful though, with only about 5700 made over about a 10-year period in the 1920s. I suspect the problem was as simple as the excessive recoil generated by the action. As I discovered shooting this example, it kicks substantially more than other comparable semiauto shotguns, and was really quite unpleasant to shoot. I cannot blame potential customers for choosing different guns (like, for example, the Browning Auto-5) that would have been available at the time.
Thanks to H. in Sweden for letting me shoot this quite uncommon shotgun!