Yuri Pasholok published another interesting piece of history on blog, this time concerning the E-100. First a bit of info from the allied sources:
This is an excerpt from the report the western allies managed to assemble on the state of the E-100 program. Notice the gun - 15cm and 17,4cm guns. That must be a typo, right?
Well, actually, it is not. Initially, the vehicle was supposed to be equipped with a "simplified" turret (the same that is currently modeled in World of Tanks), characterized by the guns being located above one another instead of next to each other - this turret was also equipped with a rangefinder, proposed in Autumn 1943 for the "regular" Maus. So far so good.
And then the German military went mental and demanded a 174mm gun to be installed into the very same turret, using the turret sketch from what was basically the good old Tiger-Maus.
Just to be clear: this gun would never ever fit inside the turret. It was way too big - which didn't bother the Germans in the slightest, they just re-drew the gun to a higher caliber and that was it. Even the 150mm gun, intended at that point for the E-100 was ridiculously big - the project counted on 15cm L/63 (!) and 17cm L/53. How "realistic" these plans were was anyone guess - even if the gun was by some miracle fitted inside the turret, there would be no space left for the crew. It was theoretically possible to make the hull and the turret even bigger, but then the vehicle would no longer be rail-transportable. The only way to make this crazy plan happen was to turn the vehicle into a SPG using this gun:
...and that was it. In July 1944, Hitler stopped the super-heavy tank development and even though the companies tried to make the project happen on their own as a private venture of sorts, nothing ever came of it except for one partially assembled hull. The work on the vehicle stopped during the winter of 1944.