Iron armour
Encyclopedia
Iron armour was a type of armour
Armour
Armour or armor is protective covering used to prevent damage from being inflicted to an object, individual or a vehicle through use of direct contact weapons or projectiles, usually during combat, or from damage caused by a potentially dangerous environment or action...

 used on ironclad warship
Ironclad warship
An ironclad was a steam-propelled warship in the early part of the second half of the 19th century, protected by iron or steel armor plates. The ironclad was developed as a result of the vulnerability of wooden warships to explosive or incendiary shells. The first ironclad battleship, La Gloire,...

s. The earliest material available in sufficient quantities for armouring ship
Ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

s was iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, wrought or cast. The use of iron gave rise to the term ironclad
Ironclad warship
An ironclad was a steam-propelled warship in the early part of the second half of the 19th century, protected by iron or steel armor plates. The ironclad was developed as a result of the vulnerability of wooden warships to explosive or incendiary shells. The first ironclad battleship, La Gloire,...

 as a reference to a ship 'clad' in iron.

Early experiments showed that wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...

 was superior to cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

, and wrought iron was subsequently adopted for naval use. Early European iron armour consisted of 4 to five inches (roughly 10 to 13 cm) of wrought iron backed by up to 36 inches (roughly one metre) of solid wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

. Experiments were also carried out with laminated armour, but these did not lead to any improvements and single plates were preferred. Many ships made during the US Civil War used laminated armour but this was necessitated by lack of facilities for manufacturing single plates of proper thickness.

While armoured ships may been built as early as 1203, in the far east
Far East
The Far East is an English term mostly describing East Asia and Southeast Asia, with South Asia sometimes also included for economic and cultural reasons.The term came into use in European geopolitical discourse in the 19th century,...

, in the Western world they first become common when France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 launched the first ocean-going ironclad La Gloire in 1859. The British Navy responded with HMS Warrior
HMS Warrior (1860)
HMS Warrior was the first iron-hulled, armour-plated warship, built for the Royal Navy in response to the first ironclad warship, the French Gloire, launched a year earlier....

 in 1860, triggering a naval arms race
Arms race
The term arms race, in its original usage, describes a competition between two or more parties for the best armed forces. Each party competes to produce larger numbers of weapons, greater armies, or superior military technology in a technological escalation...

 with bigger, more heavily armed and armoured ironclads.

Due to the ever increasing thickness of the armour, and the associated weight, proposals were made from an early date to faceharden the iron or weld steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 plates to the front face of iron armour. Efforts to carry out these proposals failed for many reasons, primarily because the metallurgy
Metallurgy
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...

 at the time was not up to the task.

By the mid to late 1870s
1870s
The 1870s continued the trends of the previous decade, as new empires, imperialism and militarism rose in Europe and Asia. America was recovering from the Civil War. Germany declared independence in 1871 and began its Second Reich. Labor unions and strikes occurred worldwide in the later part of...

 iron armour started to give way to steel armour, which promised to reduce the thickness, and therefore the weight, of the armour.

While cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

 has never been used for naval armour, it did find a use in land fortification
Fortification
Fortifications are military constructions and buildings designed for defence in warfare and military bases. Humans have constructed defensive works for many thousands of years, in a variety of increasingly complex designs...

s, 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 Prussia
Prussia
Prussia was a German kingdom and historic state originating out of the Duchy of Prussia and the Margraviate of Brandenburg. For centuries, the House of Hohenzollern ruled Prussia, successfully expanding its size by way of an unusually well-organized and effective army. Prussia shaped the history...

n government in 1868.
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