*>If two numbers are separated by a dash (-), they represent a range of values, with the larger usually for the thinner plates of the type. A slash (/) means "face maximum/back average."<*

MATERIAL Name of armor/construction material in common use at the time by the people using it. If "AVE." is in name, then the material is the average of two or more materials of the same kind made at the same time by more than one manufacturer for the same purpose, but for which separate data either is not known or is not important since the material is used interchangeably and which manufacturer's plate is used is not known.

COUNTRY Nation making this particular kind of armor/construction material.

COMPANY Manufacturer of the armor/construction material.

TIME FRAME Years that armor was manufactured or used aboard ship, as relevant.

TENSILE TENSILE STRENGTH. Test sample's minimum slow stretching force per unit original cross-sectional area needed to tear the sample into two separate parts, in pounds/square inch. The higher that this is, the stronger the metal is against slowly-increasing, non-impact loads.

YIELD YIELD STRENGTH. Test sample's minimum slow stretching force per unit original cross-sectional area needed to make the sample permanently lengthen by 2%, in pounds/square inch. The higher that this is, the stronger the metal is against slowly-increasing, non-impact loads, but only against impact loads if the tensile strength is going up by the same percentage.

Y/T Yield strength to tensile strength ratio. The closer to "1" that this value is, the less "give" the material has and more brittle the material will be if all else is equal.

% EL PERCENT ELONGATION. Percent by which the sample's length had increased just as it snapped in two. The larger the value, the more ductile the sample.

% RA PERCENT REDUCTION IN AREA. Percent of the sample's original cross-sectional area by which the narrowest point of the sample had shrunk just as it snapped in two. The larger the value, the more ductile the sample.

BRINELL BRINELL HARDNESS NUMBER. Developed in the early 20th Century in Sweden as a measure of the resistance of a material to local deformation under a near-point stress, here a tiny tungsten (wolfram)-carbide ball under a 3,000 Kg (6,614.4 lb) load. A formula for the size of the pit formed gives the Brinell Number, with wrought iron being about 100 (actually, 105 is the average) and 700 being as hard as the hardest pure cementite (actually, as the hardness goes above 650, the tiny ball begins to flatten out and the values give a greater difference than is actually there, while above 700 the tiny ball flattens out so badly that it cannot be used). This is only one of several competing hardness scales, but one of the most widely used, so I use it in place of such possibly more accurate Rockwell "C" or Vickers Pyramidal hardness scales.

USES Portions of the ship that the material is used on and why.

METALLURGICAL TERM DEFINITIONS

BRITTLE Failure of a material by sudden change from essentially no effect to total collapse in little or no time as the applied force goes above a threshold. Usually caused by the material having its yield and tensile strengths too close together, so that any yield at all immediately results in the unyielding portion of the sample next to the yielding portion having its burden increase past its tensile strength, starting an avalanche of failure as less and less of the object must try to support the entire load. If the material can "give" under the load fast enough, it can keep its net force below the tensile strength and not break or tear open until there is literally no more metal left to stop the force (soft taffy or high quality wrought iron can approximate this). Most materials have a maximum rate that a force can be applied before the object acts in a brittle manner.

DUCTILE Ability to be slowly stretched and twisted without cracking. Slowly-applied-force equivalent of tough (see below).

HARD Ability to resist being permanently deformed by an applied force on a small area.

HOMOGENEOUS Having the same metallurgical and physical properties everywhere within and on it.

SHEAR Force applied like a scissors so that it all lies in a single plane without the rest of the object being involved in the resistance to that force. Very different mechanical properties from tensile forces (see below) and much more susceptible to brittle failure. Cracks form by shear between two layers of molecules and anything that can divert or spread out the forces causing the crack can stop it in its tracks. Tough metals tend to have high shear strength, but the two are not always in line with each other; non-metallic fibers, for example.

TENSILE Force applied as a pull at each end of an object in a straight line so that it does not bend. In tests, the force is usually gradually applied to show both yield and tensile strengths.

TOUGH Resistance to cracking under sudden impact loading so that the metal has time to adjust to the force before it breaks or tears open. Usually considered the opposite of brittle (see above). The Charpy and Izod toughness tests were developed after WWI to measure how tough a material is: They take a long sample, hold one end in a vice, put a notch or groove in the sample just above the gripping point and then hit the sample sideways just above the notch/groove with a calibrated swinging or dropping hammer so that the sample must fold sharply at the notch/groove. How hard the hammer must hit the sample before it breaks or tears at the notch/groove and the manner in which the failure occurs measures the metal's toughness--tough materials should fold virtually double before splitting in two, while brittle materials snap off like pieces of a china cup dropped on a hard floor.

Laboratory specimens only. Pure ferrite (body-centered cubic crystal) at under 723° C and pure austenite (face-centered cubic crystal) above this temperature. Austenite has a hollow center in each cube cell that can hold up to 2%, by weight, Carbon, while ferrite can hold at most 0.15% Carbon. Adding Carbon to molten Iron will insert up to its maximum 2% as it solidifies into austenite, but further cooling to ferrite will attempt to expel the excess Carbon into the spaces between the individual ferrite crystals as they form. Very slow cooling will allow most of the Carbon to be so expelled, leaving only a relatively small percentage trapped in the ferrite, while fast cooling traps more and more Carbon as the cooling rate increases. The trapped Carbon chemically combines with the Iron in the ferrite to form the extremely hard and brittle cementite crystals, each cell of which is a four-sided pyramid rigidly combining one Carbon atom with three Iron atoms, with these cells interlocked like tinker-toys to form an unbending geodesic lattice of up to Brinell 700 hardness (as high as the Brinell scale goes). Mixed cementite-ferrite forms steel. The high-cementite form of steel is represented by martensite and the lower-cementite forms being bainite, pearlite, and so forth, depending on how the cementite and ferrite interleave and how much cementite exists. The optimum mixture has the ferrite acting as a support and shock-absorber and the cementite acting as the rigid back-bone and the primary strength and hardness provider. "Tempering" is the post-hardening heat-treatment where the metal is kept cool enough to prevent any austenite formation (which will allow the cementite to dissolve back into Carbon and Iron), but hot enough to allow the metal to stretch and deform to take out as many "kinks" as possible that formed during the rapid hardening water and/or oil "quench." This greatly reduces brittleness even in the hardest martensite, though the higher the Carbon content, the harder the steel is and the more brittle it will be no matter what tempering is done. Wrought iron has under about 0.08% Carbon (can be ignored) and has a very high melting point, though much less than pure Iron due to Silicon (sand) added during smelting, while cast iron has over 2% Carbon and has a very low melting point allowing it to be poured easily into molds. Steel is in the middle and its melting point varies with its Carbon content (assuming no other alloying elements to change things). Wrought iron is similar to pure Iron, being very soft but tough, while cast iron is rigid and brittle due to a large amount of cementite no matter how much it is tempered. Again, steel will go from one of these extremes to the other as its Carbon content changes, though by mechanical working and heat treatment the crystals in steel can be adjusted to combine the best of both kinds of Iron, which is why steel is so useful. Pure Iron rusts easily, so it is a poor material to use in any normal environment.

Mixture of Iron and up to 7% Silicon (from clean sand added during smelting process to lower melting point and to assist in fusing multiple plates into one). Very rust-proof due to the silicon forming an oxygen-proof surface film, though not impervious to corrosion under some conditions.

Wide range in quality. Older steels very brittle, but eventually became the high-quality material used today for most ship construction. First armor was 22" (55.88cm) vertical plates for 1876 Italian battleships manufactured by French Schneider & Co. of Gâvre, which literally fell apart when hit by large projectiles, but which could shatter any of the standard chilled cast iron projectiles then in use, preventing them from penetrating this armor even if the armor did break to pieces in the process..

Later versions used more alloying elements, but only a little Nickel was used in original "recipe." Usually used in multi-layer laminates of 1-2" (2.54-5.08cm) per layer.

Small percentage of Chromium and Nickel, but otherwise like Krupp "High-% Nickel-Steel" armor (see below). Used in Germany as HT steel was used in Britain, except that German shipbuilders tended to use much less HT-grade steel and used other methods to increase the strength of the ship structure while using regular mild/medium steels.

Developed by British Colville Co. in 1920's as "DuCol" (British Navy "D" or "D.1" grade) low-alloy, top-grade construction steel. Widely used in British, Japanese, and Italian post-WWI warships. Germany and the U.S. did not use this material through the end of WWII, preferring full armor-grade materials (STS or "Wotan" steels) when the usual mild/medium steels or HTS were not sufficient or ballistic protection was needed. After WWII, these steels became the basis of the highest grades of the commercial shipbuilding steels. (Many WWII Russian tanks were made of this steel type due to lack of sufficient Chromium and Nickel supplies.)

Up to 7% Nickel added to otherwise standard mild steel to drastically improve toughness under projectile impact. Retained as a high-strength armor support material after STS-like armors (see below) replaced it as the primary ballistic protection material. Even after being superseded by the later Chromium-Nickel-steel armors, it was used as the underlying support layer for many armored areas--U.S. battleship deck armor using STS originally had a bottom layer of Nickel-steel under the one- or two-layer STS plating and in armor-attachment bolts, nuts, and rivets. Introduction of Nickel-steel armor in 1889 by French Schneider & Co. was the reason British-developed "Compound" armor (hardened mild-steel face fused to a thick wrought iron back plate) became completely obsolete. Also, it was used as the basis of U.S.-developed Harveyized Nickel-Steel face-hardened armor introduced in 1891 (see below).

HOMOGENEOUS CHROMIUM-NICKEL FULL ARMOR-GRADE STEELS:

Also known as "Krupp Soft" or, in Krupp's own nomenclature, "Qualitat 420 Stahl." It was the same high-quality steel used for Krupp's KC face hardened armor (see below), but without the face hardening applied. Used for full ballistic protection when highly oblique impacts were expected or plate thickness was below the minimum possible for reliable KC armor manufacture (circa 3.2" (8cm) in the WWI German Navy, but later raised to at least 4.1" (10.5cm) or even higher in all nations)--"Low-%" material was considered good enough for decks because more than one layer of laminated and spaced decks and bulkheads would have to be pierced to reach the ship's "vitals" (this logic was refuted later as long-range "plunging" fire using improved projectiles with reliable delay-action fuzes became the norm after WWI). This material formed the basis of all subsequent highest-grade armor steels for ships and armored land vehicles. Also, super-strong modern U.S. Navy "HY-80" through "HY-180" submarine hull construction steels are also direct descendants of this Krupp steel armor, which alloyed Chromium for hardness with Nickel for toughness into a combination that could be heat treated to virtually any level hardness without loss of minimum toughness when properly prepared. Maximum thickness of this kind of armor used for heavy vertical plating was restricted due to an erroneous idea that ductile, homogeneous armor steel was always inferior to face hardened forms of the same steel at near-right-angles impact conditions. Testing by the U.S. Navy of such thick plates of both types showed that the face hardened armor only had an advantage when the damage that it caused the projectile was above a certain level (shatter of uncapped projectiles was always well above this level); if not, the hard, brittle face either did nothing to help or, in many cases, actually made the armor inferior to its unhardened form. As projectiles improved, the conditions where face hardening was the preferred solution became more and more limited. In fact, the U.S. Navy retained homogeneous armor for its heaviest turret faces during WWII when they discovered that it was better than any face hardened armor against their own virtually indestructible armor-piercing projectiles when hit nearly square-on, as would be the case for a turret pointed directly at an enemy warship (face hardening was retained for thinner cruiser turret faces because the hard face caused less of a problem in these lower thicknesses and because uncapped projectiles were more likely to be used against the ship). All Krupp-type Chromium-Nickel-steels were relatively corrosion-resistant due to its high 1.5-3%, by weight, Chromium content. They used 2-4% Nickel for toughness and usually circa 0.25-0.4% Carbon, though a few used 0.55-0.6% Carbon to allow easier heat treatment at some cost in toughness. All other elements except, of course, Iron were reduced to as little as possible, especially sulphur and phosphorus, which softened the metal (they were used in some non-armor steels with success).

Improved "Krupp Soft" with Molybdenum added to make it easier to process steel when red to white hot without cracking (originally Molybdenum was introduced circa 1912 by the French firm of Schneider & Co., who first developed mild steel and Nickel-steel for armor use). Equal to the best non-German homogeneous armor.

Special extra-hard form of "Wotan" armor for use on the spherical anti-aircraft directors used by WWII German heavy warships and in similar lightly-protected areas. Similar in principal to the extremely hard British and American "Homogeneous Hard" aircraft armor of thicknesses up to 0.5" (1.27cm) used to protect fighter and bomber crews, but not as extreme due to its greater thickness. Manufacture was possible because thin metal plates can be hardened (and thus strengthened) to a high level while retaining enough toughness.

British form of "Krupp Soft" high-grade armor used under similar restrictions, though the minimum thickness of British "Krupp Cemented" (KC) face hardened armor (see below) was raised slightly to make it easier to get a reliable product (face thickness was somewhat variable and the thinner the plate, the larger the effects became of such small variations) For most purposes, laminated and spaced HT steel was used in its place since WWI-era projectiles could not penetrate very deeply into a target in most cases due to over-sensitive explosive fillers (picric acid or trinitrophenol--British "Lyddite," French "Melanite," Japanese "Shimose," etc.--being the most common of cause of this problem), non-delay fuzes, and very poor penetration ability, especially at oblique impact. Also formed the basis of Japanese and Italian armors of similar type.

British high-Molybdenum-content naval armor directly replacing previous "KNC" (0.4% Molybdenum used in all NCA, the highest amount used by any manufacturer and close to the highest that can be used without degrading the plate's quality). Same composition as the standard British WWII face hardened Cemented Armor (see below) without the hard face. "D"-steel was used extensively in plates up to 2" (5.08cm) instead of NCA to reduce costs. Normally equal to any foreign armor of its type, but quality control seems to have been lax for the thinner grades during WWII, possibly due to war-time supply problems and rushed manufacture.

Italian armor replacing WWI British Armstrong KNC-type armor previously used by Italy. "D"-steel was used extensively in plates up to 1.97" (5cm) instead of PO to reduce costs. To my knowledge, this armor was equal to all foreign armors of this type, but I have little data.

U.S. Navy Bureau of Construction and Repair (later Bureau of Ships) form of "Krupp Soft" used on all portions of a warship needing homogeneous direct impact protection armor, except gun mounts and conning towers, where the very similar U.S. Navy Bureau of Ordnance "Class 'B'" armor (see below) was used. Somewhat more ductile than the average for any other form of "Krupp Soft" armor, even Krupp's post-WWI "Wotan Weich" armor. Prior to 1930, armored decks using STS were of 2- or 3-ply laminated construction using a thick underlayer of Nickel-steel armor. After 1930, STS was lavishly used for amidships hull construction above the waterline and as the foundation-layer for heavy armor plate of any kind, including more STS. Originally introduced by the Carnegie Steel Corporation (the largest of the three major naval armor manufacturers in the U.S. through the end of WWII, when it was called the Carnegie-Illinois Steel Corporation) for thinner armor, tests in 1921 of 13" (33cm) STS plates showed that homogeneous armor was superior to heavy face hardened (U.S. "Class 'A'" (see below)) armor when projectiles that neither armor could damage appreciably were employed (the Midvale Co., who also made high-quality armor-piercing (AP) projectiles, had just introduced its new 8-16" (20.3-40.64cm) "Midvale Unbreakable" soft-capped AP projectiles, which were virtually impervious to damage by most WWI face hardened armors at right-angles impacts, of which the 12" (30.5cm) Mark 15 Mod 6 was used here). Equal to the best foreign armors of its type. Note that Molybdenum was never used in this armor by any U.S. manufacturer, to my knowledge, unlike most contemporary WWII foreign manufacturers of this kind of armor.

Armor manufactured by Carnegie Steel Corp., Bethlehem Steel Corp., and the Midvale Co. was mixed together in a "crazy-quilt" arrangement, so each plate could be from any manufacturer, but homogeneous armor tended to be similar in any case (this was not true for Class "A" armor prior to 1930!). Rather high hardness. Equal to all foreign armors.

Armor still manufactured by the same three steel makers (Carnegie was now Carnegie-Illinois Steel Corp.), but now all armor of a given type was made by the same manufacturer on a given single ship, with no more mix-and-match. Significantly improved steel, but only a slight improvement in ballistic protection, since this form of armor had always had plenty of toughness (Class "A" armor (see below) benefitted much more from these improvements). The use of homogeneous Class "B" armor in turret faces (either as a single thick plate or as a not-quite-so-thick plate laminated to a 2" (5.08cm) Class "B" support plate) was an extension of the results of the 1921 tests of 13" (33cm) STS (see above), where the even more indestructible WWII U.S. armor-piercing projectiles made the situation even worse for Class "A" armor compared to Class "B" armor. (It turned out that most foreign projectiles were not nearly as good as U.S. designs at oblique impact, but this was not known at the time and might not have made enough of a difference in any event to alter the turret face plate material.) The thinner face plates used on U.S. cruiser turrets had less of a resistance difference between Class "A" and "B" and much more chance of being hit by uncapped projectiles that might be able to penetrate if the hard face was not there to shatter them, so Class "A" armor was retained. Also, Class "A" was retained on the sides and rear of the all turrets and on the cylindrical barbettes under the turrets, where the armor was thinner and was much more likely to be hit at a medium-to- high obliquity (30° and up) where the face could destroy even a high-quality projectile, though at over about 55° obliquity a ductile Class "B" armor plate would again be desirable because a ricochetting projectile might punch out a very dangerous, cork-like armor plug from a Class "A" plate, which rarely happens with good Class "B" armor, especially at high obliquity. Only Bethlehem Steel Corp. used a small amount of Molybdenum for a small range of thicknesses. Equal to the best foreign armor of this type.

High-Carbon (0.55%) replacement for both British Vickers KNC-type armor and KC-type face hardened armor (called Vickers Cemented (see below) in the Japanese Navy), in the

latter case its face hardened form was called Vickers Hardened (VH) (see below). The high Carbon content was the highest used by a successful homogeneous armor and equaled

the highest used for a successful face hardened armor (pre-WWI U.S. Midvale Non-Cemented face hardened armor (see below) had an equal amount of Carbon). This allowed

easier heat treatments to obtain a given level of hardness, but caused the plates to be somewhat brittle, though no worse than the WWI-era armor that they replaced. This armor was

kept at the same quality level as its British-developed predecessor, being somewhat inferior to most WWII-era homogeneous armors made by other countries.

Replaced older NVNC only in this single capacity; NVNC was used everywhere else in the YAMATO Class. Only slightly better than NVNC, it is not obvious whether this armor is a copy of British NCA or German Wh--the only other armors that I know used Molybdenum (I assume the French did, too, but I have no data)--or a completely in-house product. Production plates were mostly in the thickness range of 7.87-9.06" (20-23cm), though a huge 14.96" (38cm) thick MNC grating plate with many cylindrical holes was placed over the openings of the funnel uptakes to keep out projectiles; from U.S. tests, this plate would only be about 40% as resistant as a solid plate, so the effective thickness of it is only about 6" (15.2cm) of solid MNC armor (a large, inclined, several-deck-high, 1.97" (5cm) CNC plate was wrapped around most of the lower portion of the funnel above the grating, so there was less likelihood of a direct bomb hit and the CNC plate would add some small additional protection to the grating against projectiles hitting at high obliquity). As with NVNC and VH, 0.5% Copper was substituted for that amount of the strategic material Nickel as a conservation measure, with no noticeable loss of strength to my knowledge.

Nickel was in relatively short supply in Japan and a major attempt was made to reduce the amount of it in all high-grade armor. A small amount of Copper could be substituted for Nickel in the heavier plates--up to 0.5% of Nickel could be so replaced, but no more since the loss in toughness was unacceptable. However, for plates below 3" thick, it was found that Copper could replace much and, in the later CNC1 and CNC2 grades introduced during WWII, most of the Nickel without lowering the toughness below the minimum specification level because thin plates had more inherent toughness due to various scaling effects (German Wsh and British/U.S. "Homogeneous Hard" aircraft armor are examples of this). This was thus a moderately successful effort, as much more thin armor was used than thick armor (the latter was restricted to battleships in most cases). Until WWII, when combined U.S. and British efforts resulted in major breakthroughs in low-alloy steels (rarely applied to armor, however), this was the only such successful attempt by any nation.

PRE-KC FACE HARDENED ARMORS:

The armor was cast and hardened simultaneously in crescent-shaped wedges, widest and thickest in the middle where they were vertical and narrowest and thinnest at the top and bottom edges where they were sharply cut-off parallel to the ground. The wedges were soldered together with a zinc-based low-temperature solder to form a wedding-band-shaped ring with a curved profile that had a smaller diameter at the top and bottom edge than at the center of the side. The upper edge was grooved to seat a 3"-thick open-umbrella-shaped wrought iron protective roof that fit flush with the upper edge of the cast iron side and the lower edge was hidden behind a flattened-cone-shaped cement glacis that completely surrounded the turret. Two adjacent wedges had oval holes in them for gun ports and the turrets were mechanically trained in any direction. Guns ranged from 6" (15.2cm) up. The hardened face was roughly 33% of the plate's total thickness in depth and was formed by using a running-water-cooled metal mold to shape the face portion of the plate, while the rest of the plate was formed using the standard sand mold--the metal plate cooled the face very rapidly to harden it while the rest of the wedge cooled slowly. Grüson armor was of the highest quality even though the metal used was normally quite brittle. This armor could shatter even the best uncapped steel projectiles of the period with virtually no damage to the turret, even when hit in the same spot again and again. Though never used aboard ship (much too heavy), this armor formed the basis of Krupp's later "Krupp Cemented" (KC) armor after Krupp bought Herr Grüson's factory to learn his secrets. Brinell hardness values are estimates based on my knowledge of similar cast iron materials.

British answer to French Schneider & Co. solid homogeneous mild steel armor that had been introduced in 1876. At the time only the French company could make thick mild steel armor at all--22" (55.88cm) plates were made in 1876--and even they had severe breakage and brittle behavior problems that were only accepted because the steel armor could stop projectiles that wrought iron could not. The British, who could not allow the French to eclipse them and who had just had their vaunted "100-Ton Gun" defeated by the 22" French armor (the plates disintegrated in the process, but the gun could not pierce the French mild steel), decided to get the advantages of hardened mild steel without as many of the brittleness problems. They made a thick wrought iron plate and a separate 1%-Carbon steel plate, glued them together with liquid steel, heated them red-hot and rolled them into a single plate with 67-75% of the plate's thickness being the wrought iron back, and then heated the entire plate above the austenite-forming temperature and quenched it cold. The steel face hardened at its surface to about 400 Brinell (probably dropping down to circa 200 Brinell at its back where it joined the wrought iron plate), while the wrought iron plate was not changed by this heat treatment. Later Compound plates were fused together more tightly by using the wrought iron plate as the bottom of the mold for pouring the steel face, so that they fused together from the start. The Compound plate's hard steel surface caused much more damage to any of the projectiles then used than homogeneous mild steel did and this compensated for the weaker wrought iron and brittle steel face, as well as the fact that plain mild steel has never been very tough under impact shock and such all-steel plates of the period tended to break apart and not always stop the better steel projectiles. However, this complete reliance on poor projectile quality eventually killed Compound armor when Schneider & Co. introduced Nickel-steel armor (see above) in 1889 and tests by the U.S. Navy at Annapolis, Maryland, in 1890 showed the absolute superiority of the new extra-tough French Nickel-steel against the high-quality projectiles used in the test. Compound armor was made under license by all nations except France at the time, since making it was easier than solid mild steel and, until Nickel-steel and good steel projectiles arrived, just about as good. The back layer was of regular wrought iron (see above).

Mr. Harvey of the Bethlehem Iron Company (later Bethlehem Steel Corporation) was the first to develop an all-steel, single-plate, face hardened armor. It was also the first unqualified success of this kind of armor used on warships, since British Compound armor (see above) never completely proved itself superior to French solid homogeneous mild steel armor (see above). The superior performance of Grüson Chilled Cast Iron armor (see above) was due to the super-hard face shattering the projectile on its surface, prior to the projectile doing anything significant to the plate. Mr. Harvey reasoned that steel was stronger than cast iron so that the deep face was not as important as making the surface as hard as possible, even if the hard region was very thin--once the projectile nose shattered, penetration ability dropped precipitously. Mr. Harvey adopted the old "cementation" process whereby a shallow surface layer of an Iron or steel object was saturated with Carbon by packing it up against bone charcoal powder and leaving it in an air-tight, red-hot oven for several days and then heating the object above the austenite-forming temperature and quenching it, forming a thin super-hard "cemented" (or "case hardened" or "carburized") surface layer--circa 1" (2.54cm) in a Harveyized plate)--while the much lower Carbon content in the rest of the object allowed it to get only slightly harder if properly controlled.

Simultaneously with applying the Harveyizing process to mild steel plates (see above), Mr. Harvey applied it to the superior Nickel-steel armor just introduced by Schneider & Co, of France. It was obvious that a superior steel would give better results than plain mild steel if both were Harveyized. This proved to be true and Harveyized Nickel-steel armor became the armor of choice for vertical protection by all nations during most of the 1890's, being only gradually replaced by the superior "Krupp Cemented" (KC) armor that was more expensive to make due to the use of expensive Chromium in the alloy and due to the necessity of introducing and perfecting the deep-face hardening process that KC armor used. Actually, it was the introduction of soft-capped armor-piercing projectiles during this time frame that was the major deciding factor, since KC was significantly superior against them, while it was not nearly as obviously superior against uncapped projectiles that KC and Harveyized Nickel-steel armors both shattered. In both cases, the armor got an effective bonus of 30% of its thickness if it shattered a projectile at right-angles impact, with the deep face of the KC plate adding a few more percent to this, but this made the difference between the two armors less by almost a third against shattered projectiles compared to against unshattered (capped) projectiles, which were rapidly becoming the threat.

BACKING LAYER DATA ON CHROMIUM-NICKEL-STEEL FACE HARDENED ARMORS:

Later called in the German Navy "KC a/A" ("KC Old Type"), this armor was developed by Friedreich Krupp of Essen, Germany, using Herr Grüson's process for making Grüson Chilled Cast Iron armor. It was one of the first non-French major metallurgical strides in steel-making and it became the basis for virtually all later steel armors of either face hardened or homogeneous forms. It combined the Harvey "cementing" process for a thin, super-hard face to shatter projectile noses with a deep Grüson-Chilled-Cast-Iron-type face to smash the rest of the projectile after its nose was destroyed (the thin face layer was usually destroyed along with the projectile's nose and did not contribute any more to the penetration-limiting damage that the projectile suffered). As with the Grüson armor, a thick (65-67% of the plate's thickness), unhardened, extremely tough steel back layer acted as a buttress and shock absorber to keep the plate from breaking during the period when it was demolishing the projectile. Nickel toughened the plate ("High-% Nickel-steel," see above), so that a higher face hardness could be tolerated, but it did not change the rate of softening of the steel as heat was withdrawn during the quenching process, so the center of the plate would not harden properly if it was of any appreciable thickness. By adding Chromium, the plate could be hardened more easily, since Chromium also forms carbides and it changed the rate of softening, allowing the plate's center to harden even if the plate was very thick. Also, the drop in hardness between the face's surface and the depth where the soft back was reached had to be carefully controlled to keep the face from breaking (spalling) off of the back at the joint--loss of the thin cemented layer of a Harveyized plate had little effect on plate resistance, since it had done its job before the rest of the plate began to resist the shattered projectile, but loss of an appreciable part of the deep face in a Grüson-type plate radically reduces the plate's strength. By simply heating the face to above the austenite-forming temperature and keeping the back below it, and then timing how long the plate was allowed to "soak" in this condition, the point where the critical austenite-forming temperature was and the plate's inner temperature contour could be carefully controlled, allowing a deep (also called "decrementally hardened") face of practically any desired depth as well as a hardness drop at the transition layer between the fully-hardened face layer and the unhardened back that prevented any sudden crack-forming drops. If the surface was first cemented as in a Harveyized plate, the end result was a thin super-hard (600-700 Brinell) Harvey-like layer, backed by a 500-Brinell-or-so face layer just behind the cemented layer that dropped off in hardness as one went further and further from the face's surface in a hardness pattern that could be practically anything (and was as different manufacturers experimented over the years!), ultimately reaching the hardness level of the unhardened back, which was usually from 200-240 Brinell, depending on the manufacturer and date manufactured. Krupp allowed plate down to 3.2" to be face hardened using his process, as did the Austro-Hungarian firm of Witkowitzer, but most other manufacturers needed more slack, so they raised the minimum thickness to roughly 4" or higher (after WWI even Krupp itself eventually realized that 3.2" was too difficult and good homogeneous armor was not much different at such a low thickness, so Krupp raised its minimum to over 4", too). Krupp kept the depth of face almost exactly the same as Grüson Chilled Cast Iron, circa 20% of the plate, with the transition region being 13-15%, behind that (the cemented surface layer of circa 1" was considered part of the plate's face portion), and ended up with a hardened layer of 33-35% depth. Against uncapped projectiles, at normal impact this deep face added an additional 10-20% of effective thickness to the 30% effective thickness increase that the thin-faced Harvey plates got because of projectile shatter. Against capped projectiles, where the 30% shatter bonus did not occur at normal, the 10-20% increase became a more-substantial 13-26% increase.

Krupp added Molybdenum to improve ease of manufacturing, greatly increased the metal's cleanliness (general improvement in metallurgical skill by most nations), increased the steel's toughness considerably (it could now shatter soft-capped projectiles used by most nations in WWI, but not by Germany or Austro-Hungary or, after the projectile improvements due to the Battle of Jutland, Britain), increased the average back hardness, and increased the face thickness slightly to 41% total, changed the hardness contour so that the hardness drop was continuous from the back of the cemented layer to the joint of the face with the unhardened back, and increased the minimum thickness from 3.2" (8cm) to about 4.13" (10.5cm). As with the original KC a/A (see above), the surface of the face was kept as hard as possible, without the slight dip due to tempering that other foreign armor's had--they were usually hardest at about 0.25-0.5" (0.635-1.27cm) behind the face's surface. The armor was equal to the best of any other manufacturer in quality, significantly above the KC a/A level. First used as 6" (15.2cm) turret face plates on the KM DEUTSCHLAND Class pocket battleships.

Modified versions of Krupp KC a/A (see above) as made by British Armstrong, Vickers, Brown, etc. Somewhat softer face and back than KC a/A. Curved plates found to be rather brittle when hit by ricochetting German projectiles at high obliquity during WWI battles (this was not true of German KC a/A armor, as post-WWI British tests on BADEN proved).

Greatly improved KC-type armor. Thinnest--only 15% face plus a 10% transition layer--and softest (only 600 Brinell) hardened region of any WWII-era cemented face hardened armor, which made this armor the best for large thicknesses. All of the metallurgical improvements mentioned in KC n/A, including use of Molybdenum in large quantities (0.4%), employed here also. Highest backing tensile strength of any WWII-era face hardened armor.

Italian improvement of WWI KC. Somewhat lower yield strength than any other improved WWII-era KC. Assumed to still use 35% face thickness and to be up to other WWII-era KC-type armors in quality. First used on reconstructed WWI battleships. Also used for thicker vertical armor on new heavy cruisers (rare outside U.S. Navy).

Highly modified form of original Vickers Cemented (VC) armor (see above) introduced to Japan with the purchase of the IJN KONGO in 1912. Used same Vickers deep-hardening process, but increased Carbon content to 0.55% and eliminated the cementing process so that face never goes above deep-face maximum hardness. Increased average hardness of the face slightly, but kept its depth the same 35% level as VC. Minimum thickness raised to over 11" (28cm) and maximum thickness raised to 26" (66.04cm) on turret face plates. By using the Vickers water/oil quenching process on such thick plates, all VH plates from 17-26" (43.18-66.04cm) thick had a brittle crystal called upper bainite form at the center of the plates, which did not make them less effective as armor, but did cause them to snap in two through the impact point on any solid hit, which could result in secondary effects such as jamming a turret (the Japanese investigated the problem and came up with a solution, but by that time no more battleships were being built). Experimental VH plates were made and tested by the Japanese during WWII and some of these were brought to the U.S. Naval Proving Ground, Dahlgren, Virginia, after the war for testing. Most plates tested showed that they were no better than their WWI VC counterparts (which was not really that bad considering this was the best showing of any non-cemented armor production plate and that the Japanese were not trying to make better armor than VC, just make the same quality of armor cheaper). One experimental 7.25" (18.42cm) VH plate (no production VH armor on the IJN YAMATO was ever made so thin) was found to have a hardness contour very close to that of German KC n/A (without the cemented layer, of course), but was otherwise the same as all of the other VH plates in composition. However, it was found to be the best face hardened plate of its thickness ever tested at the U.S. N.P.G.! It required the late-WWII improved U.S. super-hard-capped (650-680 Brinell all the way through) 8" (20.3cm) Mark 21 Mod 5 AP projectiles to penetrate the plate in effective condition at 30° obliquity--the older Mod 3 projectiles, with a maximum cap hardness of 555-580 Brinell, were torn up badly when they penetrated and needed a significantly higher striking velocity to do so. (The U.S. test personnel were at a loss to explain this.) NOTE: The 26" VH turret face plates on the IJN YAMATO Class were inclined back 45° and were the only plates that could not be completely penetrated by any gun ever put on a warship (they could be holed at point blank range, but no projectile could pass through the hole afterwards)!

Average value of the armors made by the three major U.S. naval armor manufacturers of the time--Carnegie Steel Corporation (the largest), Bethlehem Steel Corporation, and the Midvale Company (the smallest)--based primarily on Carnegie Krupp Cemented (CKC), a slightly modified version of original Krupp Cemented armor, which was similar to the average KC-type armors made by the other two during this period. However, in an attempt to get more of this market, the two smaller armor manufacturers developed several radically different forms of face hardened Chromium-Nickel-steel armor. Bethlehem introduced in several ships from 1906-1910 a form of face hardened armor that relied completely on its deep face without the cemented layer (Bethlehem Non-Cemented Class "A" armor), which had a very large percentage of Chromium (circa 4%) and Carbon (circa 0.6%) and a rather low percentage of Nickel (circa 2%). It turned out to be very brittle and many plates cracked after installation, so it was discontinued in 1910 and a CKC-like armor was re-introduced. Later testing of 12-13.5" (30.5-34.29cm) plates of this armor in 1920-21 using the new, improved 12" "Midvale Unbreakable" soft-capped armor-piercing projectiles showed that this armor barely met minimum requirements and had no redeeming characteristics, being noticeably inferior to CKC plates. During this same time frame, Midvale also came out with its own Midvale Non-Cemented Class "A" armor (MNC) which had some rather unusual properties (see below). It too was brittle (though not nearly as bad as the Bethlehem Non-Cemented armor) and it too was discontinued in 1910, after which Midvale also reverted to a CKC-like Class "A" armor. In 1921, some problems with its armor plant, the invulnerability of the new Midvale projectiles to the CKC-type armors then in use, and the good showing of the experimental Carnegie 13" (33cm) STS plates (see above) made Bethlehem develop a form of cemented face hardened armor with only a 15% face and transition layer combined, similar to Harveyized plate, called Bethlehem Thin Chill Class "A" armor (BTC) also with unusual properties (see below) that was used in some of the last U.S. battleships and in the ships canceled by the Washington Naval Treaty. It was also made by Midvale under license in 1922 and 1923. Only Carnegie kept to its gradually improved version of CKC during this time period.

Used as portions of the armor on almost all U.S. battleships built during the 1906-1910 time frame, especially 12-13.5" (30.5-34.29cm) belt armor. Extremely constant face hardness to 25% plate depth and then a very gradual "ski-slope-shaped" hardness drop-off to the 200 Brinell level at only 18% of the plate's thickness from the back (the deepest face plus transition layer combination of any plate type that I know of). The plate used a high 0.55% Carbon to ease the hardening process somewhat, but was otherwise more-or-less standard KC composition. The high Carbon content and the very thick hard face made these plates somewhat brittle, as noted above, but not extremely so. At the time that this armor was manufactured, it, along with rival Bethlehem Non-Cemented armor (see above), was not considered unusual in any way ballistically. When some of this kind of armor was re-tested in 1921 using the new 12" (30.5cm) Midvale Unbreakable projectiles, which had remained unbroken in 90% of their tests at right-angles against any other kind and thickness of face hardened armor (including British KC and German KC a/A), the projectiles completely shattered, acting as if their armor-piercing caps were not there at all! Midvale made some more plates using their old MNC recipe, but adding a cemented face layer, and got the same result, though it was found that only a specific range of heat treatment temperatures worked (this was later understood as "temper brittleness" in the 1930's when metallurgical expertise had improved). Midvale actually made a single lot of cemented MNC-type plates that was accepted for one of the canceled battleships. However, re-testing of these plates using the newer 14" (35.56cm) and 16" (40.64cm) sizes of the Midvale Unbreakable projectiles showed that the projectiles still shattered, but the improvement in resistance dropped very steeply with increasing projectile size; a huge "scaling" effect that completely nullified any ballistic improvements when the 14" projectile size was used and actually resulted in the armor being no better than Harveyized Nickel-steel armor against soft-capped projectiles when the 16" projectile size was used (even with shatter!). The super-thick face, which failed by fracture along surfaces, not by deformation and tearing through a volume of ductile material, was the culprit. Needless to say, with 16" guns being used on all new U.S. battleships, Midvale had to abandon its MNC-type armor for a second time and started making Bethlehem Thin Chill (see below) under license until all heavy armor manufacture stopped in 1923. WWII testing with the very good hard-capped U.S. 14" Mark 16 Mod 8 armor-piercing projectile type showed MNC armor to be unable to shatter these projectiles and to be very poor ballistically, in line with the poor showing of the large-caliber projectile tests of 1921.

Developed in 1921 after some problems with the manufacture of standard CKC-type Class "A" armor (see above) halted production. During this time the very good showing of the Carnegie 13" (33cm) STS plates (see above) occurred and it also became evident that the new Midvale Unbreakable armor-piercing projectiles were practically invulnerable to damage at up to 15° obliquity (the maximum obliquity test standard during this period was circa 10° for caliber-thickness armor from any nation) from any form of then-current face hardened armor (the unusual results of the testing of MNC (see above) were not yet known). It was decided by Bethlehem Steel Corporation that a better form of Class "A" armor should be developed reflecting these facts, rather than just continuing with the current very standard slightly-modified-original-KC-type armor (see above) being manufactured in the U.S. and abroad. Since the face was not working very well against the Midvale projectiles, yet at oblique impact even Harveyized Nickel-steel armor would shatter them (it was not yet known that only soft armor-piercing caps were limited to 15-20° obliquity and that replacing them with hard--well over 300 Brinell at their forward surface--caps and then carefully controlling the projectile's hardness pattern could greatly expand the oblique impact ability of projectiles against even the heaviest face hardened armor), and since Class "B"/STS armors (see above) of similar thickness were equal to or better than Class "A" armor at low obliquity (under 20° when there was no shatter) and are high obliquity (over 55° obliquity, especially when shatter occurred, which inhibited ricochet), the designers at Bethlehem simply made a normal cemented face hardened Class "A" plate with the depth of hardened face behind the cemented surface layer reduced to only about twice as thick as the cemented layer (circa 15% of the entire plate's thickness for most plates in the 9-16" (22.86-40.64cm) range made at the time). The face was not eliminated completely since it was better than a non-face-hardened plate in the critical 20-55° obliquity region where most impacts would occur at long range due to the angle of fall if nothing else (the U.S. Navy was already specifying long-range fire supported by aircraft spotting as the "wave of the future" in naval gunnery) and since it was better against smaller uncapped projectiles under almost any conditions. When the (short-lived) good results of the very-thick-faced MNC armor occurred and the Midvale Company made a new batch of that armor with a cemented surface, the U.S. Navy had the unusual "honor" of having both the thickest-faced and thinnest-faced forms of KC-type armor ever made, as well as a more-or-less normal KC-type armor in Carnegie's CKC, being produced for its ships at the same time! When the new MNC armor type was found to have a huge scaling effect that degraded it against larger projectiles, Midvale gave up on it and began making BTC under license. The cancellation of all of those post-WWI battleships and battle-cruisers resulted in a very large amount of excess armor of all kinds being stored at the U.S. Naval Proving Ground in Dahlgren, Virginia, and other places. Some of it was used as experimental plates comparing improved projectiles between WWI and WWII and it was found that BTC armor made by either Bethlehem or Midvale could not damage the new hard-capped armor-piercing projectiles introduced by the U.S. during the 1920's, 1930's, and 1940's until the impact obliquity was increased to at least 40°, an obliquity well above the ability of any foreign projectiles to handle, as was determined by post-WWII testing of British, Japanese, and German projectiles of various types. However, since there were so many plates available, acceptance testing of large-caliber armor- piercing projectiles was performed using BTC plates at 40° obliquity during most of WWII, after an experimental period calibrating the damage these plates gave compared to modern U.S. Navy Class "A" armor, which had a very thick face (see below), of similar thickness.

When U.S. naval armor again began to be developed and manufactured for new ships and for rebuilding older battleships, the lack of ability of BTC (see above) to cause enough damage to the improved U.S. hard-capped armor-piercing projectiles being developed and introduced continuously was well known, so the trend was to increase the face depth to increase the damage-causing ability of the Class "A" armor, which was already undergoing a major improvement by the increase in toughness brought about by better metallurgical skill in general (the new plates could shatter the now-obsolete Midvale Unbreakable projectiles (see above) even at right-angles, which only Midvale's unusual pre-WWI MNC armor (see above) was known to be able to do before)--German KC n/A (see above) did the same thing, though to a much lesser degree. Unfortunately, the projectiles just kept getting better and better, so the face thickness just kept getting thicker and thicker, until a average of about 55% of the plate was face and transition layers (35-40% face and 15-20% transition layer). Even with this level of face thickness, which was the heaviest face ever used except by MNC armor, the better U.S. armor-piercing projectiles eventually became so unbreakable that the test specifications near the end of WWII said in some cases that, if the projectile could not be damaged by the armor, do not worry about it and go on to other kinds of tests! I know of at least one test where a U.S. 14" (35.56cm) Mark 16 Mod 8 hard-capped armor-piercing projectile (introduced in 1943 by the Crucible Steel Company, the largest and best U.S. naval projectile manufacturer for many years, and probably the best all-round naval armor-piercing projectile used during WWII) completely penetrated in effective bursting condition (no significant lower or middle body or fuze damage) a 13.5" (34.29cm) brand-new Class "A" armor plate at 49° obliquity at just above the Navy Ballistic Limit velocity, where the projectile just barely makes it through the plate and where maximum damage usually occurs to a completely penetrating projectile. (Such a result would be almost impossible to even imagine with any foreign projectile design!) The thick face added to the scaling effect, though not nearly as much as the face of MNC had, making thick U.S. WWII Class "A" armor somewhat inferior to German KC n/A or British CA, but also working in reverse so that U.S. WWII Class "A" armor 7" (17.78cm) or less in thickness was the best face hardened armor used by anyone ever. The replacement of Class "A" armor by Class "B" armor in the heaviest grades that were used in WWII battleship turret face plates demonstrates that the U.S. Navy was aware of the relative inferiority of its thick-faced Class "A" armor in such heavy grades against high-quality projectiles. The steel quality of this armor was equal to the best foreign armor and quality control was rather good, though Midvale armor tended to crack more than the other two manufacturers' Class "A" plates (Carnegie-Illinois Steel (later U.S. Steel) Corporation and Bethlehem Steel Corporation).

ADDITIONAL BITS AND PIECES OF NAVAL ARMOR INFORMATION:

20th-CENTURY FRENCH NAVAL ARMOR

My knowledge of French naval armor is very limited, but I know that it introduced many of the basic metallurgical improvements used by armor and construction steel during the 19th and early 20th Centuries. The following are some information that I know of concerning French naval armor in the 20th Century:

1) France introduced Molybdenum in 1912 to improve the manufacturing process for naval armor by increasing the hardenability and toughness of the steel and by making the metal tougher when in its high-temperature solid austenite form. This indicates to me that French WWI-era armor was the equal to the best foreign armor, at least in standard manufacturing processes, steel quality, and so forth.

2) French naval designers decided during the 1930's that steeply-falling armor-piercing aircraft bombs would be more of a threat than more shallow impacts by medium-to-long-range naval gun projectiles and they therefore had face hardened armor used for all plates over 4" (10.2cm) on turret and conning tower roofs where layered protection (spaced decks) was not possible. To my knowledge, no other nation did this. Ironically, while this idea turned out to be absolutely true in almost every case in WWII, the one case where a French main turret roof--a 5.91" (15cm) roof plate on the battle-cruiser DUNKERQUE--was hit was not by an aircraft bomb, but by a 15" (38.1cm) 1938-pound hard-capped armor-piercing projectile at about 70-75° obliquity fired by the HMS HOOD at close range. The projectile broke in half and the nose ricochetted off, but the plate had a large, projectile-shaped hole in it (it actually seems to be an outline of the British projectile on its side pushed into the plate!), throwing a large amount of plate material into the turret at high velocity, followed by the lower portion of the projectile, which then exploded (probably a less-than-full-strength explosion, but what difference did it make?) inside the turret, knocking out the right half of the split 4-gun mount (each turret was divided by heavy internal armored bulkheads into two adjacent 2-gun turrets on one mount, a unique French design). If the armor had been homogeneous, the projectile would have ricochetted off in one piece and probably no armor would have been ejected from the plate hit.

3) French WWII-era armor test results (I have a couple) give their face hardened armor a perfect fit for an armor of the best WWII-era plate quality using the 35% face of original German KC armor (i.e., Krupp WWII KC n/A with a Krupp WWI-era KC a/A face).

WWI-ERA AUSTRO-HUNGARIAN KC-TYPE ARMOR MADE BY WITKOWITZER

The firm of Witkowitzer made all of the face hardened armor for the last Austro-Hungarian battleships. The minimum thickness was, just like Krupp's own KC a/A, 3.2" (8cm) for vertical plate and the heaviest plates were 11" (28cm) thick. Tests by the Austro-Hungarian Navy using their own latest Skoda 12" (30.5cm) armor-piercing projectiles, which closely resemble Krupp's latest 12" projectiles (Krupp's "30.5cm Pzgr.m.K. L/3,4") indicate that these plates were significantly superior to all other face hardened plates made through the end of WWI, being almost as good as WWII-era face hardened armor was (about 95% as good compared to Krupp KC a/A which was only about 83% as good) when it used the standard 33-35% face of original KC a/A. In fact, I would give it virtually all WWII-era properties, making it the first of the super-tough face hardened armors that would always shatter soft-capped armor-piercing projectiles in the same way that U.S. Midvale Non-Cemented (MNC) (see above) did, but without the plate quality and scaling effects that cost the U.S. MNC armor effectiveness against larger or better-designed, hard-capped projectiles. The composition of Witkowitzer plates is the same as normal KC a/A plates, but Witkowitzer seems to have been the first to have developed a toughening process combined with a good post-hardening temper that prevented the face layer from prematurely cracking under initial impact shock, which occurred with all other armors of the period except MNC (due to MNC's face being so thick that the needed shock to crack it all of the way through was large enough to ensure that the soft-capped projectiles would shatter first and to the lucky accident that the Midvale Company had discovered how to avoid "temper brittleness" by the correct heat treatment temperatures, which was only generally understood well after WWI).

PRE-WWI KRUPP KC a/A ARMOR TESTING LIMITATIONS

Krupp never improved their KC a/A armor from its initial 1894 state because they continued to test the armor with uncapped armor-piercing projectiles (to keep a consistent data base and because Krupp was conservative almost to the point of psychosis!) though by 1898 the primary threat was from capped armor-piercing projectiles, which could survive the initial impact shock and thus required the plate's face layer be toughened to keep it from shattering if the projectile didn't first. (The post-WWI statements that British armor was better than German armor was indeed true for KC plates, though absolutely not true for any other kind of armor.) The drastic improvements that led to WWII KC n/A show that Krupp had no technical reason for their inferiority. (Tests MUST always be designed to make sure that the thing being tested performs its purpose (e.g., its reason for existing), not something that is easy to test, but which is not the actual thing that must be done!)