PzKpfw VI Tiger I, or SdKfz 181.

The frontal vertical plating was massive enough to withstand virtually anything.	The armor was so effective that the Allies had to develop special tactics to deal with the Tiger.

The hull of the Tiger was a comparatively simple welded unit with a one-piece superstructure welded on top. At the front it was 100 mm, around the sides 80 mm, and 26 mm on the top. To assist production all shapes were kept simple. The turret was also simple, and the sides were almost upright. It remains a curious fact why Henschel's engineers came up with what was essentially a square box for the Tiger's hull. The only steeply sloping element on the Tiger was the short glacis plate, forward of the hull upper front plate with its ball-mounted machine gun and driver's vision slots, which was set at 81 degrees to the vertical. However, the vertical plating was massive enough to withstand virtually everything. The mantlet was very heavy, with 120 mm of armor, and carried the long and heavy gun. Below, the armor tables for the Tiger I:

According to Jentz (JENTZ, Thomas L.; Germany's TIGER Tanks - Tiger I and II: Combat Tactics; op. cit.), "The Tiger's armor was invulnerable to attack from most tank guns firing normal armor-piercing shells or shot at ranges over 800 meters, including the American 75 mm and the Russian 76 mm. It is obvious that the 17-pdr. firing normal APCBC rounds could defeat the frontal armor of the Tiger I at most combat ranges for tank vs. tank actions in Europe. However, by 23 June 1944, only 109 Shermans with 17-pdrs. had landed in France along with six replacements. By the end of the war, on 5 May 1945, the British 21^st Army Group possessed 1,235 Sherman tanks with 17-pdrs., while the remaining 1,915 Sherman tanks were all equipped with the 75 mm M3 gun". Below, three more tables from the same source (JENTZ, Thomas L.; Germany's TIGER Tanks - Tiger I and II: Combat Tactics; op. cit.), that show clearly the tactical superiority the Tiger I had over its contemporary adversaries:

The armor of the Tiger I was not well sloped, but it was thick. Here is where many fail to understand that, in terms of World War II tank warfare, thickness is a quality in itself, since armor resistance is mainly determined by the ratio between armor thickness and projectile diameter (T/d). The T/d relationship regarding armor penetration demonstrates that the more the thickness of the armor plate overmatches the diameter of any incoming armor piercing round, the harder it is for the projectile to achieve a penetration. On the other side, the greater the diameter of the incoming projectile relatively to the thickness of the armor plate which it strikes, the greater the probability of penetration. This explains why the side armor of the Tiger I, being 80 mm thick, was so difficult to be penetrated at combat ranges by most Allied anti-tank and tank guns, whose calibers were overmatched by the thickness of the Tiger I armor. The quality of the armor was another major asset of the Tiger I, and it can't be emphasized enough that the Tiger I was a very special kind of Panzer, since it had the best quality of everything, compared to any other German tank. The rolled homogeneous nickel-steel plate, electro-welded interlocking-plate construction armor had a Brinell hardness index of 255-260 (the best homogeneous armor hardness level for WW II standards), and rigorous quality control procedures ensured that it stayed that way. The Tiger I's armor was much superior to that of, for example the Panther, which armor had a much higher Brinell index, and consequently, was very brittle. The Tiger, as a side effect from the usage of this special armor, also was a very expensive tank. The nominal cost of a Tiger was 250,000 Reichsmarks. In contrast, a PzKpfw III cost RM 96,200, a PzKpfw IV RM 103,500, and a PzKpfw V Panther RM 117,000; all these figures are exclusive of weapons and radios.

Another fact that helped the Tigers a lot was the "shatter gap" effect which affectted allied ammunition, a most unusual situation where rounds with too high an impact velocity would sometimes fail even though their penetration capability was (theoretically) more than adequate. This phenomenon plagued the British 2 pounder in the desert, and would have decreased the effectiveness of U.S. 76mm and 3" guns against Tigers, Panthers and other vehicles with armor thickness above 70 mm. It should be noted that the problems with the 76 mm and 3" guns did not necessarily involve the weapons themselves: the noses of US armor-piercing ammunition of the time turned out to be excessively soft. When these projectiles impacted armor which matched or exceeded the projectile diameter at a certain spread of velocities, the projectile would shatter and fail.

Penetrations would occur below this velocity range, since the shell would not shatter, and strikes above this range would propel the shell through the armor whether it shattered or not. When striking a Tiger I driver's plate, for example, this "shatter gap" for a 76mm APCBC M62 shell would cause failures between 50 meters and 900 meters. These ammunition deficiencies proved that Ordnance tests claiming the 76 mm gun could penetrate a Tiger I's upper front hull to 2,000 yards (1,800 meters) were sadly incorrect.

As a general rule, BHN (Brinell Hardness Index) effects, shot shatter, and obliquity effects are related to the ratio between shot diameter and plate thickness. The relationship is complex, but a larger projectile hitting relatively thinner plate will usually have the advantage. There is an optimum BHN level for every shot vs plate confrontation, usually in the 260-300 BHN range for World War Two situations. Below that, the armor is too soft and resists poorly, above that, the armor is too hard and therefore too brittle.

The 13.(Tiger) Kompanie, of Panzer Regiment Großdeutschland, reported on the armor protection of the Tiger: "During a scouting patrol two Tigers encountered about 20 Russian tanks on their front, while additional Russian tanks attacked from behind. A battle developed in which the armor and weapons of the Tiger were extraordinarily successful. Both Tigers were hit (mainly by 76.2 mm armor-piercing shells) 10 or more times at ranges from 500 to 1,000 meters. The armor held up all around. Not a single round penetrated through the armor. Also hits in the running gear, in which the suspension arms were torn away, did not immobilize the Tiger. While 76.2 mm anti-tank shells continuously struck outside the armor, on the inside, undisturbed, the commander, gunner, and loader selected targets, aimed, and fired. The end result was 10 enemy tanks knocked out by two Tigers within 15 minutes"  (JENTZ, Thomas L.; Germany's TIGER Tanks - Tiger I and II: Combat Tactics; op. cit.).

All this considered, and analyzing the tables above, it stands clear that, "based on opposing ranges, without considering other factors, the Tiger I had only been outclassed by the Russian Josef Stalin heavy tank with the 122 mm gun" (Again, JENTZ, Thomas L.; Germany's TIGER Tanks - Tiger I and II: Combat Tactics; op. cit.). The rule of thumb was that it took at least five American M4 Sherman medium tanks to knock out a cornered Tiger. When speaking of opposing ranges, it becomes necessary to take a look at another essential Tiger I feature: the KwK 36 L/56 8.8 cm gun.

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