the thicker plates are stronger than a laminated stack of thinner plates - with rolled hardened steel armor. the flexing is the start of failure, the thinner plates are defeated in detail, thick plates are stronger because they don't yeild as soon
spalling is a problem - they used splinter decks
The Nathan Okun Naval Gun and Armor Data ResourceThus, with plates that follow the Linear Velocity Rule (and ignoring any other effects on the projectile due to the impact at the moment), using anything but single solid plates is clearly inferior to the single solid plate case, with the laminated case varying in its amount of reduction depending on the materials used (I usually spit the difference between the solid plate and the spaced plate cases when I calculate the laminated case, which works for most ductile plates that can form petals or plugs depending on the projectile nose shape and impact obliquity).
please see multiplate pdf
ARMORThe US Navy after WWI, when determining the resistance of two laminated plates of the same type, simply assumed that the upper plate was reduced by 30% -- was only 70% as strong -- as to its thickness and then physically added to the complete thickness of the lower plate. For example, if the upper plate was 5" STS and the lower plate was 2" STS, the total effective deck thickness, regardless of the angle of impact or projectile type, was T(deck) = (0.7)(5) + 2 = 5.5" compared to 7" of total weight. This is quite a loss of strength for the weight, so there had better be a very good reason for not using a solid 7" plate.
http://www.eugeneleeslover.com/ARMOR-CHAPTER-XII-A.html1210. Summary of armor development.-It will be seen from the preceding review that each change in armor has added something, and that modern armor contains all the essentials of each successive product. First, for marine use, we had the simple wrought-iron armor, which was later developed into compound iron-steel armor. Then all-steel armor displaced the compound armor, and was, in turn, improved by the addition of nickel. Next we have a return to the hard face principle, but with homogeneous structure, in the application of Harveyizing. Finally we have the introduction of chromium and the development of decremental hardening as applied to both cemented and non-cemented plates.
here is some data to illustrate - using the most modern battleship gun - the Alaska class 12"
note the lower velocity to defeat a thinner plate - the upper plate will be defeated, and the next plate will be attacked by the remaining velocity in the projectile - the thicker plate requires substantially more velocity to defeat
12” AP PROJECTILE MARK 18 (1,140 LB) (NEW IN REV. “J”):
These were for new ALASKA Class cruiser guns only. The remaining 12”-gunned battleships still used their old 12” Mk 15 MOD 6 “Midvale Unbreakable” (1916-vintage) shells, usually with new Mk 21 Base Detonating Fuzes.
In 500 projectile lots (except for initial lots, as specified by BuOrd).
3 projectiles for ballistic test from each lot;
1 projectile for fragmentation test from 1st lot only (unless further tests needed for some reason);
6 projectiles for flight test from 1st lot of new contract (range table verification) and 3 for flight test from each 5th lot thereafter (quality control).
Maximum Striking Velocity in any test was 2,300 ft/sec.
Ballistic Test Against Class “B” Armor @ 50° Obliquity:
Plate Thickness Striking Velocity (ft/sec)
5.0” 1,300 (1221 adjusted to 35 deg)
Ballistic Test Against Class “A” Armor @ 35° Obliquity:
Plate Thickness Striking Velocity (ft/sec)
Modern laminated tank armor is a different animal - it is thicker and lighter by volume and addresses different threats than were faced by battleships
Last edited by USSWisconsin; 12 Feb 12, at 15:35.
"If your plan is for one year, plant rice. If your plan is for ten years, plant trees.
If your plan is for one hundred years, educate children."
On battleships, the reasons for not always using a thick plate instead of laminated plates was to permit the ships to be built using the methods available at the time - the back plate was typically structural - supporting the thick plate in front of it and adding to the strength of the armored structure or hull. The armor plate at the back of the stack (away from the enemy) was part of the ship's structure. The heavier plates were normally attached with armor bolts. The joints in the rear plate were arranged so they didn't correspond to the joints in the armor facing. so if an enemy projectile hit one of the joints - there would not be another joint behind it - the back plate would be solid with no joints at that point. The front plate would as thick as possible and the rear plate as thin as possible to maximize protection.
This is forged steel armor we are discussing - not Chobham armor or other modern designs - armor has developed greatly since the 1930's designs used in the final battleships. Modern tank armor is still described as RHA equivalent - and modern plates of ~8 or 9" are often rated as 20 or 30 inches of RHA on modern MBT's. Spalling has been addressed in many ways - it is still an issue - but modern armor systems handle it differently than battleships did.
Battleships used splinter armor behind the primary armor, and the use of KC face hardened armor was restricted to the belt on the final battlships, since turrrets and conning towers were located where slinters from the hard face would be very destructive. These structures above the deck or inside the ship normally used NKC armor - a more homogeneous version of KC (Krupp Cemented) armor to reduce the hardened splinters which were caused by an AP projectile impact. Krupp armor evolved greatly during the WWI to WWII period and the final versions were as much improved over the first examples as nickel steel was over wrought iron.
In general battleships evolved using these major types of iron based armor:
- Wrought Iron (first hammered then rolled - the ships using this type were commonly referred to as ironclads)
- Compound armor (steel plates bonded to a wrought iron backing)
- Nickel Steel (other types of solid steel armor were also used - but not as universally, for example: France used other types like Cruesot armor)
- Harvey armor
- Krupp armor
Some medium thickness plates (~ 6") tested at the end of WWII had a equivalence to RHA of 2.8 - the best performance recorded for Krupp armor.Armor Types
Early Efforts: The earliest attempts to construct ships with protection involved thick hardwood, and they were remarkably successful on large ships, and during the Age of Sail this was the usual method well into the 19th century. There are some references to protective bronze plates on warships in antiquity. The use of crude iron plates was recorded as far back as the 12th century. This early armor was primarily used to resist fire and arrows and protect smaller ships which couldn't carry an equivalent protective thickness of hardwood. Cast iron was popular as armor due to its cost, but its brittle nature made it more susceptible to shattering under the impact of even early guns. The high cost of metal armor usually relegated it to a few small ships intended to spearhead an attack, and its use was limited. The impact on buoyancy on these early armored ships was considerable, and there were many failures, which tended to discourage the practice.
Wrought Iron: As artillery improved and cannon balls were replaced with conical shells, often with explosive filling, wooden ships became increasingly vulnerable. Major Paxihans developed the flat trajectory explosive shell firing gun, which saw its first major combat in the Russian Crimean War, after several smaller debuts in other conflicts. The Russians had invested in these guns, and though they were poorly equipped in general, the use of these weapons allowed them several decisive victories over their enemies. France and Britain suffered and hastily began to devise armored ships. Improved cast iron armor was used effectively in land fortifications where weight was not a problem, but in equivalent thicknesses it was decidedly inferior. Considerable testing was undertaken in the late 1850's and the results showed that wrought iron armor was the best available solution. This normally consisted of 4” - 5” of hammered wrought iron attached to a thick hardwood backing. Iron of this thickness was difficult to produce with the technology of the times, so many armored ships used multiple layers of boiler plate to achieve the thickness desired. Boiler plate was the highest quality iron available at the time, and was not used as a cost saving measure, but rather it was the best they could do with the materials at hand. The multiple layer solution was inferior to a single thick plate, as the layers were defeated individually by projectiles, whereas the single plate required higher energy to breach, thus the layered solution, typically using 1” plates, had to be almost twice as thick to achieve the same results. As wrought iron developed, rolling became the preferred method of improving its resistance, rolled plates were also tempered and annealed to strengthen them, with efforts being made to differentially harden the outside face while maintaining a soft backing to resist cracking, these efforts were to resurface later with steel armor.
Mild Steel Armor: As cannon improved through the 1870's the thickness of wrought iron required to resist the effects grew to 22”. At the same time the recently developed Bessemer steel process was making steel available in quantities suitable for the armoring of ships. Steel plates were prepared using rolling and oil quenching and demonstrated a 45% improvement in resisting the effects of contemporary guns, however these plates proved more susceptible to cracking than wrought iron and were not durable enough to withstand repeated hits.
Compound Armor: The desire to produce armor with a hard face lead to the idea of placing a layer of steel on a wrought iron backing in the late 1870's. The methods of welding the steel to the iron included pouring molten steel into the space between the plates, and brazing the plates together with copper. Molten steel was also poured on top of wrought iron to form the hard steel face layer with the resulting plate being rolled to about half of the original thickness. The compound plates were about one third steel and two thirds wrought iron. These methods all saw use and each had some advantages and disadvantages, but in general compound armor was successful at the time, being gradually improved over time and stayed in use for about 10 years as the best available armor type. In general compound armor exhibited a 25% improvement over high quality wrought iron and had no serious disadvantages. Armor piercing ammunition improved at the same time and by the late 1880's forged chromium steel shot was able to defeat compound armor while improved alloy steel armor was able to resist its effects.
Nickel Steel: The use of alloys in steel was the next major step in improving armor. Nickel proved particularly effective as an alloy and the resulting nickel steel represented the next major improvement in armor technology. Nickel steel was not as difficult to produce, though it was expensive compared to compound armor and was about 5% more effective or about 30% better than wrought iron. The primary cost shifted from labor to materials, since nickel was not a commonly available substance at the time. The nickel provided toughness to the steel while at the same time allowing it to be hard enough to shatter incoming projectiles, but it still had some problems with cracking, and had some disadvantages over the previous compound armor. It had a relatively short lifespan due to rapid advances in armor technology, though nickel continued to be used in later types of armor.
Harvey Armor: Starting with a nickel steel plate, Harvey armor applied heat treatments, the face was hardened by carburizing or cementation, and the back was annealed to toughen it. This American development provided all the benefits of compound armor with less chance for delamination. The results were widely acclaimed around 1890 and proved to be about 55% better than wrought iron and almost 20% better than plain nickel steel. The grain pattern was improved and impurities forced out the armor billets by low temperature forging. Once the sprue portion of the billet was trimmed away, the finished ingot was rolled to thickness before final heat treatment. The surface was treated by holding the steel at near molten temperatures for long periods with a layer of powdered carbon on the outside face to produce a high carbon layer about an inch deep. This hard face was able to shatter most armor piercing projectiles while the tough back held the armor together and prevented it from shattering. The process was labor intensive and time consuming, taking months or even years to produce the plates. Water baths gave way to spray jet cooling of the plates, eliminating steam layers which insulated the steel. Additional alloys were introduced to Harvey armor, including chromium, manganese, phosphorus, sulfur and silicon. The processes developed for Harvey armor included many breakthroughs in metallurgy, which benefited the production of the later Krupp armor.
Krupp Armor: This was the final step in battleship armor developed by Krupp in Germany around 1893, and was similar to Harvey armor with some significant advances, the carbon was added by gaseous cementation, using hydrocarbon gas. This allowed the hard surface layer to be more closely controlled and considerably deeper. Improvements were also made to the base alloy with the introduction of greater amounts of chromium and other alloys like manganese and copper. The annealing process was developed to produce a fibrous microstructure in the tough backing portion of the plate. The hard face was up to 40% of the plate's thickness in some examples and Krupp armor was adopted by most battleship makers by the early 20th century. There was a 20% improvement over Harvey steel and about 85% over wrought iron plate, allowing armor to be considerably thinner with the same resistance, saving weight and space. For example 14” Krupp armor was equivalent to 25.5” thick rolled wrought iron armor. Krupp armor itself was continuously improved and its alloy composition and heat treatments updated to produce Krupp Cemented (KC) armor, which had an extremely hard face, this further improved its resistance by ~10% under certain conditions where a shell hit perpendicular to the plate, but had some detrimental effects like spalling when the plate was hit obliquely. This lead to Krupp Non- Cemented (KNC) armor which used a similar alloy composition but did not have the extremely hard face of KC, this proved more suitable for many surfaces where spalling and splinters from the face would cause the most damage, like armored decks, and turret faces. The KC armor continued to be favored for external surfaces like the belt, KNC was used where splinters were a concern like surfaces inside the ship or on deck. Both were a substantial improvement over the original Krupp armor and were up to two and a half times as effective as wrought iron.
STS: Special Treatment Steel was a high yield strength (~110,000 psi) armor grade steel used for structural work on US battleships, it was weldable, machinable, and homogeneous, it did not have a hard face. Other nations developed similar versions but were more sparing in the use of this expensive material. This material was normally used as an attachment surface for heavy KC or KNC plates, but was also used for splinter armor and armored decks and bulkheads and was normally limited to thicknesses under 4”. It was about 70% more effective than wrought iron armor.
Underwater Protection: The double bottom was an early example of underwater protection, this was extended to the double hull, and this system was sometimes extended to triple or even quadruple hull. Multiple watertight compartments to minimize the effect of underwater damage were incorporated into ships as early as the 3rd or 4th century in Chinese junks. The detailed compartmentalization of ships below the waterline became a feature of the best battleship designs. The outer compartments were frequently filled with a buoyant material like cork or wood to exclude water in the event of flooding. Coal bunkers in early steam warships proved to be effective at absorbing the force of underwater torpedo or mine explosions, their exclusion when ships converted to oil caused many concerns over protection. Many different arrangements were tried and the torpedo blister gained widespread acceptance since it could be retrofitted to earlier ships. The main idea was to dissipate the force of an explosion by allowing an expendable space to be consumed in absorbing the force of the explosion, but preventing the ship from flooding. It was found that heavy armor on the skin of the ship was detrimental because of the splinters generated by an explosion. The ideal solutions involve relatively light ( ~13mm - 25mm) ductile outer shell plating, which will tear and fold in an explosion and not create splinters when hit. The ideal configuration tested was a system of alternating void and liquid filled layers. The Richelieu was a particularly effective design with outer and inner voids filled with light weight water excluding foam “pillows”, a center liquid loaded space held fuel or sea water ballast. The USS Tennessee had another excellent system with an outer air void, three liquid loaded layers, and air void and then the armor bulkhead, another water tight compartment was located behind the armor. The voids were each three to six feet in depth, and had many compartments to control flooding. Some were less effective, like the Pugliese system which had a large “crush” drum in a massive cylindrical void on each side, the concave inner bulkhead concentrated the force of explosions and frequently failed the ships which used it (Italian Littorio class), the Soviets and Dutch both planned to use the system, which was claimed to be effective against a 1,000 # TNT charge (it was breached on several occasions by 180# aircraft torpedoes). The armor belt was located inside the hull and sloped downward, this helped direct the for of an explosion down or outboard from the critical armored raft in the core of the ship. The armored raft had an armored inner bottom, above the triple keel, and the sloped belt was connected at the top by the heavy armored deck, and closed on the ends by the heavy armored end bulkheads, which were as thick as the belt. With the armored raft located inside a honey comb of small compartments, made of ductile steel which crushes rather than shattering when hit by a torpedo warhead or mine, the ship was well protected, and could survive several hits from known enemy weapons.
Modern MBT armor can have an RHA equivalence of over 4.0 with special formulations like DU used in their lamaniated designs - they also address HEAT, HESH and hypervelocity Kinetic penetrators that were not considered in the battleship designs.
Last edited by USSWisconsin; 01 Mar 12, at 17:30.
"If your plan is for one year, plant rice. If your plan is for ten years, plant trees.
If your plan is for one hundred years, educate children."
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