Ed D sends us the Kugelpanzer (“spherical tank”) - a mysterious, one-person, ball-shaped armored vehicle built by Nazi Germany during World war II.  Featuring just 5mm of steel armor and a tiny 25-horsepower engine - it remains a historical anomaly.  Only one prototype is known to exist.  It was captured by the Soviet Red Army in 1945, and today is on display at the Kubinka Tank Museum in Russia.  The tank’s secrets are closely guarded by the Russians. Its original olive green paint was covered in a gloss-grey. Its internal components, including the engine, were completely stripped - and taking metallurgical samples is completely forbidden. After almost 80 years, no one knows what it is even made of. The Kubekpanzer will likely remain one of the larger mysteries in tank design.
More pics and information here.