Armor Protection
GENERAL COMMENTS: This was the most complex category in terms of trying to
quantify and simplify a rating. After all, each of these vessels was designed to operate in a different anticipated threat environment than the others. Bismarck, for instance, was designed for combat in the North Atlantic. Her designers anticipated weather and visibility conditions such as had prevailed at Jutland in WWI. As a result, she was optimized for short-range, flat-trajectory combats. Her armor scheme reflects this, with an armor layout that makes it fantastically difficult to put a shell into her vitals at short range, but which is vulnerable to long-range fire, and which reduces the total amount of protected volume in the vessel by carrying her armor deck lower in the ship than her contemporaries. By the same token, Yamato was simply built to stand up to and utterly outclass any conceivable American or British opponent by sheer weight of gunfire, and elephant-like armor. As such, hers is a sort of 'brute force' approach to protection. Her armor layout isn't the most efficient, but she has a lot of armor, so it doesn't really matter. American and French battleships were designed to do less with more, with the South Dakota, for instance, being perhaps the best protected warship, pound for pound, ever built. One reason the Americans in particular came out with such good designs is that they could afford to. America poured tons of money into making the propulsion plants of their vessels more efficient, meaning that the resulting ships were relatively smaller and armor box correspondingly small. This, in turn, led to the ability to use the armor more heavily in the protected region. By the same token, American BBs, alone of contemporary battleship designs, had hull plating and interior works which were constructed entirely of Special Treatment Steel (STS), a very tough light armor steel, whereas contemporary designs usually reserved such steels for important splinter-proofing locales. The United States alone was capabe of affording such extravagances.
I based my ratings extensively upon the work of Nathan Okun. From his
paper detailing the usage of Bismarck's 15"/47 gun to shoot at all seven of 'The Contenduh's', I extracted a quantification of the total zones of vulnerability, for both deck and belt armor, of each of the seven ships. If you want the really gory details on how I did this,
click here. Suffice it to say that I am surprised as you that Iowa has the most effective belt armor of the lot; I would have bet on Yamato any day. But Iowa's combination of an inclined belt, and a highly effective STS-steel shell plate outboard of the belt (which has just enough resistance to strip the AP cap off of an incoming shell) tips the score in her favor. Richelieu also had this same design, and very good protection as a result. Bismarck, despite the reputation of her side armor, fares very poorly in this category. From a deck armor perspective, Yamato comes out on top, followed closely again by Richelieu and Iowa. Vittorio Veneto is very vulnerable to high-angle fire, and Bismarck is as well. Yamato thus emerges as the best armored of the lot, followed closely by Iowa and Richelieu. This makes perfect sense to me, as Yamato also had the distinction of carrying the only armor plates which were completely impervious to any battleship weapon ever mounted afloat -- her 660mm turret faceplates. She was, indeed, an awesome beast. It makes the American and French feats of achieving protection within a hair as good, on much smaller displacements (particularly the South Dakota, which has the second smallest displacement of the seven warships detailed here), a very impressive feat as well. On the bottom of the heap, Vittorio Veneto and Bismarck were both penalized for their inability to cope with a long-range gun duel. Bismarck also suffered from the poorest belt armor of the lot.
http://www.combinedfleet.com/b_armor.htm