The smart Ar 231 was an ultra light-weight floatplane conceived in the early WW2 years to be carried and operated from submarines. Its main unusual feature was an offset wing design to enable its two wing panels to fold aft flat in its watertight stowage tube without interfering with each other, the inner section was designed on a slant so the right wing was in fact lower than the left. Tested thoroughly during 1940, the design couldn’t get over its inherent fragility, lack of power and awful air/seaworthiness qualities. Only a bunch of prototypes were built.
At any rate, a superbly elegant failure with some clever engineering behind it.