Originally Posted by EPPaar
True, but the Retina I manual shows the shoe and illustrates it with their "Pocket Rangefinder".
The "accessory" (aka "flash") shoe began life as a mount for accessory RFs and later VFs. Flash units were originally too large for such a small mount and only later evolved into units that could mount in the shoe.
I'm not sure where/when the shoe began life, but I do believe it was the original Leica that gave the now common size its start. There, it was the attachment point for the accessory RF. Accessory VFs weren't needed for a number of years until models with interchangeable lenses were introduced.
The same goes for the Retinas. The Retina's original design followed several leads from Leitz. Nagel Kamera Werke designed the Retina to be somewhat Leica compatible, utilizing a Kodak cassette that was compatible with the Leica cameras.