Krupp armour was a type of steel naval armour used in the construction of capital ships starting shortly before the end of the nineteenth century. It was developed by Germany's Krupp Arms Works in 1893 and quickly replaced Harvey armour as the primary method of protecting naval ships, before itself being supplanted by the improved Krupp cemented armour.
The initial manufacturing of Krupp armour was very similar to Harveyized armour; however, while the Harvey process generally used nickel-steel, the Krupp process added as much as 1% chromium to the alloy for additional hardness. Even though use of chromium in steels predated the use of nickel, the necessary amount of chromium complicated steel case-hardening due to its liability to crack (hence water tempering had to be replaced with slower oil-tempering). [1]
Also, while Harveyized armour was carburized by heating the steel and placing charcoal on its surface for long periods (often several weeks), Krupp armour went a step further. Instead of inefficiently introducing carbon at the surface with coal, Krupp armour achieved greater depth of carbon cementation by applying carbon-bearing gases (coal gas or acetylene) [2] to the heated steel. Once the carburization process was complete, the metal was then transformed into face hardened steel by rapidly heating the cemented face, allowing the high heat to penetrate 30% to 40% of the steel's depth, then quickly quenching first the superheated side then both sides of the steel with powerful jets of either water or oil.
Krupp armour was swiftly adopted by the world's major navies; ballistic tests showed that 10.2 inches (25.9 cm) of Krupp armour offered the same protection as 12 inches (30.4 cm) of Harvey armour.
By the early twentieth century, Krupp armour was rendered obsolete by the development of Krupp cemented armour (also "Krupp cemented steel", "K.C. armor" or "KCA"), an evolved variant of Krupp armour. [3] The manufacturing process remained largely the same, with slight changes in the alloy composition: in % of total – carbon 0.35, nickel 3.90, chromium 2.00, manganese 0.35, silicon 0.07, phosphorus 0.025, sulfur 0.020. [4] [5]
KCA retained the hardened face of Krupp armour via the application of carbonized gases but also retained a much greater fibrous elasticity on the rear of the plate. This increased elasticity greatly reduced the incidence of spalling and cracking under incoming fire, a valuable quality during long engagements. Ballistic testing shows that KCA and Krupp armour were roughly equal in other respects. [3]
Developments in face-hardened armour in the late nineteenth and early to mid-twentieth centuries revealed that such armour was less effective against glancing oblique impacts. The hardened face layer's brittleness was counterproductive against such impacts. Consequently, alongside face-hardened armour such as KCA, homogeneous armour types that combined ductility and tensile strength were developed to protect against glancing impacts. [3] Homogeneous armour was typically used for deck armour, which is subject to more high-obliquity impacts and, on some warships such as Yamato class and Iowa class battleships, for lower belt armour below the waterline to protect against shells that land short and dive underwater.
Examples of such armour include German Wotan weich (Ww) and US special treatment steel (STS) and Class B homogeneous armour. [6]
An alloy is a mixture of chemical elements of which in most cases at least one is a metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Most alloys are metallic and show good electrical conductivity, ductility, opacity, and luster, and may have properties that differ from those of the pure elements such as increased strength or hardness. In some cases, an alloy may reduce the overall cost of the material while preserving important properties. In other cases, the mixture imparts synergistic properties such as corrosion resistance or mechanical strength.
Armour-piercing ammunition (AP) is a type of projectile designed to penetrate armour protection, most often including naval armour, body armour, and vehicle armour.
The three Maine-class battleships—Maine, Missouri, and Ohio—were built at the turn of the 20th century for the United States Navy. Based on the preceding Illinois class, they incorporated several significant technological advances over the earlier ships. They were the first American battleships to incorporate Krupp cemented armor, which was stronger than Harvey armor; smokeless powder, which allowed for higher-velocity guns; and water-tube boilers, which were more efficient and lighter. The Maines were armed with four 12-inch (305 mm) guns and sixteen 6-inch (152 mm) guns, and they could steam at a speed of 18 knots, a significant increase over the Illinois class.
Rolled homogeneous armour (RHA) is a type of vehicle armour made of a single steel composition hot-rolled to improve its material characteristics, as opposed to layered or cemented armour. Its first common application was in tanks. After World War II, it began to fall out of use on main battle tanks and other armoured fighting vehicles intended to see front-line combat as new anti-tank weapon technologies were developed which were capable of relatively easily penetrating rolled homogeneous armour plating even of significant thickness.
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:
Carburizing, or carburising, is a heat treatment process in which iron or steel absorbs carbon while the metal is heated in the presence of a carbon-bearing material, such as charcoal or carbon monoxide. The intent is to make the metal harder and more wear resistant. Depending on the amount of time and temperature, the affected area can vary in carbon content. Longer carburizing times and higher temperatures typically increase the depth of carbon diffusion. When the iron or steel is cooled rapidly by quenching, the higher carbon content on the outer surface becomes hard due to the transformation from austenite to martensite, while the core remains soft and tough as a ferritic and/or pearlite microstructure.
Case-hardening or carburization is the process of introducing carbon to the surface of a low carbon iron or much more commonly low carbon steel object in order to enable the surface to be hardened.
Kashima was the second ship of the two Katori-class pre-dreadnought battleships built for the Imperial Japanese Navy (IJN) in the first decade of the 20th century, the last to be built by British shipyards. Ordered just before the start of the Russo-Japanese War of 1904–1905, the ship was completed a year after its end. She saw no combat during World War I, although the ship was present when Japan joined the Siberian Intervention in 1918. Kashima was disarmed and scrapped in 1923–1924 in accordance with the terms of the Washington Naval Treaty of 1922.
Harvey armor was a type of steel naval armor developed in the early 1890s in which the front surfaces of the plates were case hardened. The method for doing this was known as the Harvey process, and was invented by the American engineer Hayward Augustus Harvey.
Compound armour was a type of armour used on warships in the 1880s, developed in response to the emergence of armor-piercing shells and the continual need for reliable protection with the increasing size in naval ordnance. Compound armour was a non-alloyed attempt to combine the benefits of two different metals—the hardness of steel with the toughness of iron—that would stand up to intense and repeated punishment in battle. By the end of the decade it had been rendered obsolete by nickel-steel armour. However, the general principle of compound iron was used for case-hardened armour, which replaced nickel-steel in the mid-1890s and is still used today.
Iron armour was a type of naval armour used on warships and, to a limited degree, fortifications. The use of iron gave rise to the term ironclad as a reference to a ship 'clad' in iron. The earliest material available in sufficient quantities for armouring ships was iron, wrought or cast. While cast iron has never been used for naval armour, it did find a use in land fortifications, presumable due to the lower cost of the material. One well known example of cast-iron armour for land use is the Gruson turret, first tested by the Prussian government in 1868. Armoured ships may have been built as early as 1203, in the far east. In the West, they first become common when France launched the first ocean-going ironclad La Gloire in 1859. The British Navy responded with HMS Warrior in 1860, triggering a naval arms race with bigger, more heavily armed and armoured ironclads.
37 mm anti-tank gun model 1930 (1-K) was a Soviet light anti-tank gun used in the first stage of the German-Soviet War.
The Katori class was a two-ship class of pre-dreadnought battleships built for the Imperial Japanese Navy (IJN) in the early 1900s. As Japan lacked the industrial capacity to build such warships itself, they were designed and built in the UK. They were the last pre-dreadnought battleships to be built for Japan at overseas shipyards, and the last to be equipped with a ram. The ships were delivered after the end of the Russo-Japanese War of 1904–1905. They saw no action during World War I, although both were present when Japan joined the Siberian Intervention in 1918. They were disarmed and scrapped in 1923–1925 in accordance with the terms of the Washington Naval Treaty of 1922.
The Tsukuba-class cruisers were a pair of large armored cruisers built for the Imperial Japanese Navy (IJN) in the first decade of the 20th century. Construction began during the Russo-Japanese War of 1904–05 and their design was influenced by the IJN's experiences during the war. The British development of the battlecruiser the year after Tsukuba was completed made her and her sister ship Ikoma obsolete, as they were slower and more weakly armed than the British, and later German, ships. Despite this, they were reclassified in 1912 as battlecruisers by the IJN.
The French cruiser Pothuau was an armoured cruiser built for the French Navy in the 1890s. She spent most of her active career in the Mediterranean before becoming a gunnery training ship in 1906. The ship participated in the Kamerun campaign early in World War I before she was transferred to the Red Sea and the Indian Ocean in 1916 where she patrolled and escorted convoys. Pothuau fruitlessly searched the Indian Ocean for the German commerce raider Wolf in mid-1917. The ship resumed her previous role after the war until she was decommissioned in 1926 and sold for scrap three years later.
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Special treatment steel (STS), also known as protective deck plate, was a type of warship armor developed by Carnegie Steel around 1910.
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