The Arado Ar 231 was designed to go into a six foot diameter tube that went on top of a submarine. The Arado Ar 231 could be assembled in six minutes.
The Arado Ar 231 could fly for about 4 hours.
The Arado's weak point was that it couldn't take off if a wind was more than 20 knots.
The project was cancelled in favor of the Focke-Achgelis Fa. 330, which was a helicopter.