Reuter designed the J12 as four-seated aircraft. Most parts of this design were taken from the J10, like the wing, the rear and front parts of the fuselage and the undercarriage. The new design feature of the J12 was a new center fuselage, which was wider and higher than on the J10 and which should accomodate the cabin for passengers and the pilot seat. This J12 design was already available in January 1919, but a cabin mockup showed, that the demands for passenger convenience could not be fullfilled with the small J12 cabin. Therefore the complete J12 design was aborted and a new design was started under the designator J13.

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