They weren't "largely inferior" to German armor.

http://www.reddit.com/r/AskHistorians/comments/2rbp07/when_did_the_concept_of_having_separate_tanks_and/cnepj64

Weak on what way? It could kill Panzer IVs and Stugs till the end of the war, and with the upgraded 76mm gun, it could take on Tigers no problem. And battles like Arracourt showed that it really came down to training and experience, and by 44 we undoubtedly had the better crews.

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Neither of those things are true either. The front of the Sherman was 51mm thick and sloped at 56 degrees. This gave it the equivalent of 90mm of armor on the front of the hull and the gun shield was 89mm thick. The thickest armor on a late model Panzer IV was 80mm, and only 50mm on the front of the turret. The Shermans armor certainly wasn't as thick as a Tigers, which had 100mm on the front hull (only 10mm more than the Sherman) and 120 on the front of the turret. But then the Tiger was a heavy tank.

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No. The Panzer IV armed with the 7.5cm KwK L/43 could not penetrate the front of the Sherman above about 500 meters, well within the Shermans ability to kill it. The Panzer IV armed with the 7.5cm KwK L/48 couldn't penetrate the front of the Sherman beyond about 1100 meters, still within the Shermans ability to kill it.

He also posts a great overview in this thread.

This simply isn't true, and when the evidence is examined you will see that US forces did quite well. In a study of 87 tank engagements involving involving the 3rd and 4th Armored Divisions the US actually destroyed more enemy tanks and equipment then they lost, and in these engagements they were quite often fighting Panthers.

In the first 3 examples in the study, which involved a total of 27 engagements, a total of 155 M4s faced off against 114 Panthers. The US lost 10 M4s while the Germans lost 70 Panthers

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And the Sherman had been designed from the get go to fight other tanks. In FM 17-10[11] it states explicitly that both medium and light tanks should be used to fight other tanks. In 1942 the Sherman was more than capable of taking on any tank on the battlefield. Its 75mm gun could kill any German tank at the time and with 90mm of armor on the front of the hull (effective) it was mostly impervious to any German tank except at close range.

This situation remained about the same until mid 44, yes the Panzer 4 was upgunned, but even the 7.5cm KwK L/48 couldnt penetrate the front of the Sherman beyond 1100 meters while the Panzer IV remained vulnerable from about the same distance.

It is an extremely pervasive myth that German armor was this unbeatable juggernaut that the Allies, especially the Sherman, could not touch. The 76mm Shermans could penetrate Tiger armor reliably and they regularly did...but without the added negative of all the issues German heavy tanks like the Tiger suffered from. It's more important to get tanks to the field, not break down while in the field, and able to accompany infantry to the objective, than to have a kick-ass paper weight that sits pretty in the depot waiting for a new transmission. See the Battle of Arracourt wherein the US Shermans with the supposed "puny" 75mm gun inflicted a 3:1 kill ratio against the German Panthers. See the Battle of the Bulge wherein US infantry using mainly bazookas and 57mm guns held up entire Tiger and Panther columns.

Heavy tanks simply did not work. It's been the cold hard reality of war since the Battle of Kursk in 1943. Patton was absolutely correct - and the lightning reconquest of France was largely due to the efforts of Third Army and its Sherman tanks. You do not fight Tigers in head to head combat. You bypass the Tigers, hit their supply depot, and laugh as their transmission conks out and the crew is forced to abandon their expensive and hard-to-maintain heavy tank once it has run out of fuel and spares; German Tiger's took a lift/crane to get its body off to do maintenance, Shermans could be operated on in the field with easily replaced parts; that's the type of disparity of quality we're talking here.

Here's the facts:

• The German armor could only engage M4's in the range where Shermans could engage back.

• The M4 outclassed every German tank (see: North Africa) up until into 1944 and then the upgrade to the 76mm along with general quality of the M4 it was more equalized rather than this brutal surpassing of quality.

• The Tiger Tank was a glorified bunker which spent more time in a depot than on the field. Yes they were fancy but they were hardly capable of performing the action tanks are supposed to do: Take out fortified positions while advancing with the infantry, providing cover for infantry, and exploit breakthroughs with speed.

• Regardless the 76mm M4 Sherman gun could penetrate Tiger armor at 1000 meters.

• The Panzer III, intended to be Germany's main battle tank, was totally and completely outclassed by the M4 Sherman. The IV, the 'Panther', only came into the field in '44 and that was the first tank that could truly and consistently stand up to American produced AFV's.

• While on paper the Panther was superior to the M4 (and T-34) in reality the exact opposite was true; T-34 and M4 crews both shit on Panther crews consistently. The Russians/Western Allies had better trained crews, an abundance of support (especially via air power and infantry which is how war is won, not technical contests), and the fact that it was, as /u/TheHIV123 has said numerous times, was only a minute list of advantages in reality.

So I'd argue the M4 Sherman was far more 'quality' than the Tiger w.r.t. performing duties a tank is supposed to do. It wouldn't break down, it was easily repaired in the field, it had radio communications, it from a technical standpoint was more or less equal with its medium tank contemporary in the German army or superior depending on the year, and it consistently outkilled German tanks in the field.

There is something getting rather lost in this thread.

Tanks are not like fighter aircraft whose sole or main purpose is to destroy other aircraft and binary comparisons of one tank's armour, for example, against another is a very superficial analysis.

Tanks are a part of the combined arms weapons system. Real life is not World of Tanks. There is infantry, aircraft, barbed wire, inclines, infantry, artillery, mine fields, infantry, anti-tank ditches, logistics, infantry, production costs, ease and speed of construction, infantry, reliability, maintainability, infantry and infantry.

Did I mention infantry? Because that's what matters in war. Only infantry can occupy and hold ground and the primary function of all other facets of combined arms warfare is to allow the infantry to occupy and hold ground.

The efficacy of any tank must therefore be measured in a holistic manner, and not in a reductionist stats analysis. For example, one contributor states

A Panther threw it's standard AP round at twice the velocity of the standard 75mm Sherman AP round (936m/sec vs 519m/sec).

And? So what? Is the velocity of the main armament the principle determinant of how good a tanks is? Is armour penetration even the principle determinant of how good a tanks is? And the answer is obviously "No".

If this was the case then the 2pdr and 6pdr guns on early to mid war British tanks would have imbued them with a firm superiority. In fact, these guns were totally unsuitable as tank guns because they could not fire a meaningful HE round and were thus ineffective against infantry, artillery, and just about anything else on the battlefield that wasn't a tank.

Not only that, but these uber high velocity improbably long boom-sticks that the Germans mounted on their late war tanks were a liability in close terrain (hedges, forests, urban areas), while the muzzle blast kicked up dust, stripped leaves from bushes and trees, and were a menace to any supporting infantry who might be in the vicinity.

So a very high velocity gun is useful for shooting up armour, but its less useful for everything else. And how important is shooting up other tanks? Well, analysis conducted by the western allies indicates that only around 14% of all tank casualties were caused by other tanks which is about the same as losses to panzerfausts.

Which simply reinforces the point that primary purpose of a tank is otherwise than killing other tanks. Again, this was a central pillar of pre-war British armoured doctrine and it was proved horribly misguided.

So in evaluating how good a certain tank was against another we need to evaluate everything. Including speed and cost of production, ease of supply, ease of maintenance, reliability, transportability, and value as an infantry support tool.

And in all of those factors, the Panther and the Tiger fall flat on their faces. Hell's teeth, would you buy a new car if the manufacturer estimated it would suffer a catastrophic transmission failure before your first visit to the petrol station? Or a car that had to be fitted with an automatic fire extinguisher in the engine bay because of the frequency of engine fires? Of course you wouldn't, yet this was the kind of design feature built into the Panther.

So while the Panther and Tiger seem good on paper in the world-of-tanks reductionist-stats-analysis kind of way, actual events showed that the rather more humble allied tanks like the T-34, Churchill and M4, were a better weapons system overall.

One interesting thing to note about the Panther tank was that the pre G models (and even a number of Gs due to production problems) came with a shot trap on the gun mantlet. The gun mantlet was theoretically impossible for a 75mm gun on the Sherman to penetrate. However, due to the shot trap, a hit on the lower part of the gun mantlet could ricochet downwards onto the top hull armour which was only about 15mm thick. This was if the Panther turret was facing forwards, which it would probably be due to tanks usually facing what they're engaging.

However, as talked about below, Shermans didn't come with the best optics so hitting a target like the gun mantlet (I'm not aware if the Allies were aware of the shot trap) on purpose would be a tall order at range.

If you're looking for the simplest, most accurate answer, it is this:

Germany invited the United States to the war, but it didn't have the decency to have the war someplace that the U.S. could get to by land. American tanks had to be shipped across an ocean. They had to be as small and as light as possible while still maintaining as much functionality as they could so that as many as possible could be sent with each shipload. German tanks, obviously, were used on the same continent on which they were manufactured, so they could be parked in Dieter's garage at night, and in the morning he just hopped in and carpooled to wherever the boss was holding the battle.

Secondary to that consideration is the fact that there was a majority of high-ranking officers and officials in the War Department and in the Army that did not want to understand before the war how important tanks were in modern warfare. Tanks debuted in the Great War, but as far as many key officials were concerned, the jury was still out as to whether tanks would become an integral part of military doctrine. For that reason, only a small part of the budget was used for developing and producing tanks until later in the war.

The latter situation was not nearly as significant as the former, however.