Flettner FI 282
Most people don’t associate the development of helicopters with World War II, but in fact, prior to the beginning of the war the German Luftwaffe experimented extensively with choppers, and the first accepted design was the open cockpit Flettner FI 282.
One of the oddest features of the aircraft was its intermeshing rotors, which meant that the two main rotors angled away from each other though the arc of the blades crisscrossed. But they were very carefully synchronized so as not to collide with each other. This design gave the chopper the advantage of not needing a tail rotor in order to offset the engine torque on the main rotors. And as you can see from the picture above, the helicopter was designed with just a minimal frame attached to an engine.
The Luftwaffe was nevertheless impressed with it and ordered 1,000 FI 282s. The German air service envisioned using the new aircraft for observation and reconnaissance, anti-submarine warfare, and other roles.
But by the time the chopper was ready for full production, it was 1944 and the Luftwaffe was occupied fighting a defensive air campaign against encroaching Allied bombers and fighters. As such, the ordered fleet of Flettner choppers was never built. And in any event, shortly after production began, the Allies bombed the production facility, destroying it.
The good news — for the Allies — was that after the war the engineer who designed the FI 202, Anton Flettner, immigrated to the U.S. and helped design choppers for the U.S. military.