It's little wonder that people get such funny ideas about German engineering in the WWII era. I mean, look at Wikipedia's partial list of "Wunderwaffe":
Type XXI U-boat
Type XXIII U-boat
Panzer VIII "Maus"
Landkreuzer P. 1000 Ratte
Landkreuzer P. 1500 Monster
Jets and rocket-propelled aircraft
Heinkel He 280 - the first jet fighter
Messerschmitt Me 262 the first operational turbojet fighter/bomber
Messerschmitt Me 163 "Komet" the first operational rocket-propelled fighter
Focke-Wulf Ta 183 jet fighter
Arado Ar 234 - the first jet bomber
Horten Ho 229 "flying wing" jet fighter/bomber
Bachem Ba 349 manned rocket-propelled interceptor
Silbervogel sub-orbital antipodal bomber
Heinkel He 162 jet fighter
Flettner Fl 282 "Kolibri"
Focke Achgelis Fa 223 "Drache"
Bombs and explosives
Fritz X air-to-ship glide bomb
Henschel Hs 293 glide bomb
German nuclear energy project
V-3 cannon "Hochdruckpumpe" (a multi-stage cannon)
Fi 103 (V1) - the first cruise missile
A4 (V2) - the first mid-range ballistic missile
Rheinbote - the first short-range ballistic missile
Wasserfall supersonic ground-to-air missile
Hs 117 Schmetterling ground-to-air missile
Enzian ground-to-air missile
Ruhrstahl X-4 wire-guided air-to-air missile
Fliegerfaust/Luftfaust hand-held automatic rocket launcher
Sturmgewehr 44 - the first assault rifle
Sturmgewehr 45 - prototype
Zielgerät 1229 Vampir night-vision equipment
FG 1250 Tank Mounted night-vision equipment
(Links to articles on at least most of these can be found in the article.)
You may have heard of some of these; if you follow this blog, you might have heard of the Schwerer Gustav (seen in a video in this post about GaoGaiGar). While not the longest ranged or absolute largest-caliber gun ever built, it was the biggest. (It didn't see much action-it mostly just demolished some fortifications and an ammo dump or two during a very heavy artillery action.) It wasn't a very practical weapon; when assembled, it needed two parallel sets of train tracks in order to move. But this was hardly the craziest place German engineering went during the war.
Aside from many innovations that became common, Hitler called for the construction of other weapons comparable to Gustav. (Trivia note: If you've ever heard of a cannon called "Big Bertha," Bertha Krupp was the wife of Gustav Krupp, and the original guns were named for them. No joke.) One of the more ambitious, not to mention totally insane, was the Landkreuzer Ratte.
What was the Ratte? Well, first, its name probably comes from another relatively similar (although less ambitious) vehicle called the Maus (also in the above list). The Maus was the largest tank ever built. Maus=mouse, and Ratte=rat. This should begin to give you an idea of how the Ratte compared to the Maus, which weighed 188 tons. The Ratte, had it been built, would have been a minimum of 1000 tons, and analysis indicates it would have been more likely to come out to a final weight of around 1800 tons-ten times the size of the Maus. (The Maus, incidentally, never saw combat-mechanical problems bogged the prototype down while it was in transit, and it was blown up in an effort to keep it out of Russian hands.)
The Ratte would have been armed with a naval turret, so massive that ordinary tank shells would have been worthless against it, and armed with a bank of anti-aircraft guns-much like a naval vessel of the time, hence the name "Landkreuzer" (landcruiser).
While hardly the first megatank concept, the Ratte is probably the most impressive. It also came in a time when it was already obsolete-as air power proved in the WWII naval combat theaters, battleships, which the Ratte basically was, were rapidly becoming obsolete. Not only did the Ratte suffer from being an obsolete concept, it further suffered from being a poorly considered one-the Ratte's sheer size would have made it very, very slow, meaning it could have been bombed from very high altitudes with reasonable accuracy. Travel would have been awkward in any case-it would have been far too heavy for any bridge, although its clearance would have let it ford rivers, and it would have destroyed any road or town through which it might have travelled. (Incidentally, the Ratte and other crazy proposed superweapons are documented in a book called My Tank is Fight!, a book that I must read at some point.)
Is it any wonder that comic book authors came up with this kind of stuff? I think not.