During the preparation for Operation Seelöwe - the invasion of England - it soon got clear, that the Kriegsmarine needed a high number of landing crafts. Therefore all branches of the German Army made proposals for such a craft - the Luftwaffe proposal was is known as the Siebel-Fähre (Siebel Ferry) named after its inventor, Oberst Siebel.
The Siebel-Ferries were constructed from existing material, pioneer pontoon originally used ot build auxiliary pontoon bridges. Two of those pontoons were connected side-by-side, a propulsion unit with BMW aircraft engines was added in the back and a large platform mounted on top of the pontoons was used to carry the payload. Vehicles could enter or leave the craft over a ramp on the bow of the ferry.
There were multiple version of those crafts build, from transport crafts over artillery ferries to staff command ships or hospital ferries. The drawing shows one version of a transport ferry.