In an alternate 1950s cold war, the Soviet Union and the United States (and their NATO and Warsaw pact allies) are locked in an arms race not unlike our own. What's the difference you ask? Instead of nuclear weapons as the weapon of choice to make bigger and better, the superpowers are competing to create the largest and most powerful battle tank, think along the lines of Super-Heavy tanks such as the Maus, Tortoise or T28.

My question is this- How large can one of these vehicles be without compromising armament or armor so that the tank can move (or so the ground doesn't collapse from the immense pressure of the tank's tracks)?

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    $\begingroup$ What are the limitations? The real-world tanks arms-race started producing lighter & faster tanks instead of slower & heavier ones, I assume you have reasons for that not happening? Do tanks need to be ATVs or can they run on train tracks and similar? Min-Speed? etc. pp. $\endgroup$ – dot_Sp0T Aug 16 '18 at 20:10
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    $\begingroup$ Note that large tanks are simply large targets for any helicopter or ground attack airplane equipped with anti-tank missiles. There is a reason why nobody makes large tanks. $\endgroup$ – AlexP Aug 16 '18 at 20:10
  • $\begingroup$ You are going to want to get your hands on any of the Ogre games by Steve Jackson games. Although most of the tech is late 21st century, some of the ideas expressed could easily be retrofitted on 1950's hardware. $\endgroup$ – Henry Taylor Aug 16 '18 at 20:16
  • $\begingroup$ Maus was almost 200 tons, and it could still move. Further progress in engines can make heavier vehicles viable. You should look into mining excavators. Ground will not "collapse" unless you drive on swamps (see wikipedia entry on Power Shovel). The key constraint was bridges, and threat from airplanes $\endgroup$ – Bald Bear Aug 16 '18 at 20:22
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    $\begingroup$ MBT's evolved to the sizes and weights they are because MBTs have to fit on rail cars, in planes, on ships, on ordinary roads and in tunnels and over bridges (and indeed fit with existing systems and support vehicles). People tried bigger tanks and basically everyone goes for an MBT design now because it works. Massive vehicles have "traditionally" been the products of massive egos - competent engineers and military people don't want them. $\endgroup$ – StephenG Aug 16 '18 at 20:49

There is no real limit as to how large a vehicle could be and still move, assuming that you actually want as big of a vehicle as possible.

Armor of a given thickness actually makes up a smaller percentage of a vehicles weight the larger that vehicle is, because the armor weight only increases by surface area, while the total weight increases by volume. Armor weight increases by the power of 2, other weight by the power of 3. This means that larger vehicles can have thicker armor, or can spend that saved weight on other needs.

Allowing the vehicle to move is relatively simple; just keep adding engines until it can. Divide the tracks into segments and have each engine work a single segment. Sinking into soft soil isn't much concern either, just make the tracks wider. The ground pressure of an M1 Abrams tank is only twice that of a person. If you wouldn't sink when standing on one foot, neither would the Abrams. Crossing rivers isn't either, assuming your tank is truly gargantuan. Who cares about finding a strong enough bridge, just ford the river. But there's a problem. Tanks don't generally drive strategically-relevant distances under their own power. How are you getting your super-tank on a train? What about a ship? A tank this big would be a nightmare to repair, meaning you only want it running (and suffering wear and tear) in battle. Not driving 500 miles to battle.

As others have said, tanks much bigger than real ones are easy targets for airstrikes. Especially before the modern day. Some nations have tested active defenses on tanks to protect against ATGM's, but these are still rare and not super effective. If you can provide your super-tank with some kind of point-defense system to shoot down incoming bombs or ATGM's, it could deal with air attack.

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    $\begingroup$ The smallest bridge that the tank has to reasonably cross is the upper bound on how big a tank can be. (In WW2, the cranes that lifted tanks into ships defined the maximum size of American tanks.) $\endgroup$ – RonJohn Aug 16 '18 at 20:59
  • $\begingroup$ @RonJohn It's the upper bound for sane people, yes. The Germans just invented snorkels for their biggest tanks and had them ford rivers where big bridges were unavailable. en.wikipedia.org/wiki/Deep_wading $\endgroup$ – Ryan_L Aug 16 '18 at 21:03
  • $\begingroup$ That assumes all rivers are less than 10(?) feet deep, which is patently absurd. No wonder they lost the war!! $\endgroup$ – RonJohn Aug 16 '18 at 21:05
  • $\begingroup$ @Ryan_L, are you implying that finding creative solutions to complex problems is a sign of insanity? If you are right, this site is even more of a nuthouse than I already thought! $\endgroup$ – Henry Taylor Aug 16 '18 at 21:05
  • $\begingroup$ @RonJohn, perhaps all rivers deeper than 10 feet had bridges large enough for German tanks. Stop picking on the Germans! They lost the war because the economic advantage was on our side. Prior to nuclear and biotech warfare, economics always determined the victor. $\endgroup$ – Henry Taylor Aug 16 '18 at 21:07

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