Arado's Tiny Folding Seaplane Was Impressive, But Useless
The Imperial Japanese Navy made considerable use of submarine-launched seaplanes during World War 2. Although less well-known, the Kreigsmarine also laid down a small number of aircraft carrying submarines just before the war.
Their aircraft was to be the Arado AR-231, which was an impressive feat of engineering, but ultimately one that tried to do too much in too small a package. It did, however, play a small role in the sinking of the Stephen Hopkins, one of the most valiant last stands made by a ship during the Second World War.