Just for the record, Bertoni designed the exterior. French engineers designed the suspension and mechanicals. The engine was the same as the one used in the Traction Advant. The DS was a combination of Italian-penned styling and French engineering. By the way, the Traction Advant was solely designed by the French, and it represented a huge step forward in design and engineering when it came out in the late 1930s.
There was a D-21 running around Iowa City in 1970 and I got a chance to drive it for about 15 minutes. I noticed the steering wheel seemed to ooze into the steering column and the brake pedal looked like a small mushroom. Very strange.