Christie had a few crazy designs, like a flying tank. I think it was called the M1919 or something...
Anyway, it had no turret and had only three MGs pointing out of the sides. It had a biplane frame attached to the top and a prop powered by the tank's engine. The Russians also tried it out after hearing about it.
A fantastic read about massive WWII war machines that were near-impossible is "My Tank is Fight!" by Zack Parsons. It has the Horten 229 (used that part for a school project), the Landkreuzer, the USS Habbakkuk, the V3 supergun, and the German space and nuclear programs, and a few others. I definitely recommend giving it a read.