Panzer VIII Maus (“Mouse”) was appropriately called “an incredible piece of pointless engineering” (actually, most of Nazi Wunderwaffen deserve this label).
It was intended to punch holes through enemy defenses as an immense “breakthrough tank“, whilst taking almost no damage to any components. Which in 1944 was a wishful thinking because it was vulnerable at least to landmines and on the Eastern front to the 152mm guns of SU-152 and ISU-152 tank destroyers.
Besides, there was a fundamental problem of getting the 188-ton monster to the battlefield as no train could carry it and no bridge could survive it. Crossing any bridge was thus impossible, so it was planned to have the VIIIs operate in pairs, one crossing the stream on electrical power, provided by a cable from the second, the air being supplied through a long snorkel.
However, it was, indeed, an impressive piece of engineering – with 200-220mm frontal armor, two guns (128mm and 75mm) in a rotatable turret it was the heaviest tank (actually, any enclosed armored fighting vehicle) ever built.
Just five tanks were ordered, but only two hulls and one turret were completed before the testing grounds were captured by advancing Soviet military forces.
After the war, the Soviet Commander of Armored and Mechanized troops ordered the hull of V1 (“prototype 1”) to be mated with the turret of V2. The Soviets used six German FAMO-built 18t German half-tracks, the largest half-track vehicles that Germany built in the war years, to pull the 55 ton turret off the destroyed hull.
The combined V1 hull/V2 turret vehicle was completed in Germany and sent back to the USSR for further testing. It arrived there on 4 May 1946. When further testing was completed the vehicle was taken over by the Kubinka Tank Museum for storage where it is now on display.