Iron armour was a type of
naval armour
Naval armor refers to the various protections schemes employed by warships. The first ironclad warship was created in 1859, and the pace of armour advancement accelerated quickly thereafter. The emergence of battleships around the turn of the 20t ...
used on
warship
A warship or combatant ship is a naval ship that is used for naval warfare. Usually they belong to the navy branch of the armed forces of a nation, though they have also been operated by individuals, cooperatives and corporations. As well as b ...
s and, to a limited degree, fortifications. The use of iron gave rise to the term
ironclad
An ironclad was a steam engine, steam-propelled warship protected by iron armour, steel or iron armor constructed from 1859 to the early 1890s. The ironclad was developed as a result of the vulnerability of wooden warships to explosive or ince ...
as a reference to a ship 'clad' in iron. The earliest material available in sufficient quantities for armouring
ship
A ship is a large watercraft, vessel that travels the world's oceans and other Waterway, navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally disti ...
s was
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
, wrought or cast. While
cast iron
Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its car ...
has never been used for naval armour, it did find a use in land
fortification
A fortification (also called a fort, fortress, fastness, or stronghold) is a military construction designed for the defense of territories in warfare, and is used to establish rule in a region during peacetime. The term is derived from Lati ...
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 (; ; Old Prussian: ''Prūsija'') was a Germans, German state centred on the North European Plain that originated from the 1525 secularization of the Prussia (region), Prussian part of the State of the Teutonic Order. For centuries, ...
n government in 1868. Armoured ships may have been built as early as 1203, in the
far east
The Far East is the geographical region that encompasses the easternmost portion of the Asian continent, including North Asia, North, East Asia, East and Southeast Asia. South Asia is sometimes also included in the definition of the term. In mod ...
. In the West, they first become common when
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
launched the first ocean-going ironclad ''
La Gloire'' in 1859. The British Navy responded with
HMS ''Warrior'' in 1860, triggering a naval
arms race
An arms race occurs when two or more groups compete in military superiority. It consists of a competition between two or more State (polity), states to have superior armed forces, concerning production of weapons, the growth of a military, and ...
with bigger, more heavily armed and armoured ironclads.
Early experiments showed that
wrought iron
Wrought iron is an iron alloy with a very low carbon content (less than 0.05%) in contrast to that of cast iron (2.1% to 4.5%), or 0.25 for low carbon "mild" steel. Wrought iron is manufactured by heating and melting high carbon cast iron in an ...
was superior to
cast iron
Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its car ...
, and wrought iron was subsequently adopted for naval use. British efforts at perfecting iron armour were headed by a government Special Committee on Iron, formed in 1861 by
War Secretary Lord Herbert for the continued research into naval armour. Among its members was Sir
William Fairbairn, a noted
civil and
structural engineer
Structural engineers analyze, design, plan, and research List of structural elements, structural components and structural systems to achieve design goals and ensure the safety and comfort of users or occupants. Their work takes account mainly of ...
who had also built over 80 iron vessels before retiring from shipbuilding. Other members included
metallurgist
Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys.
Metallurgy encompasses both the ...
John Percy, civil engineer
William Pole and representatives of the
Royal Engineers
The Corps of Royal Engineers, usually called the Royal Engineers (RE), and commonly known as the ''Sappers'', is the engineering arm of the British Army. It provides military engineering and other technical support to the British Armed Forces ...
,
Royal Artillery
The Royal Regiment of Artillery, commonly referred to as the Royal Artillery (RA) and colloquially known as "The Gunners", is one of two regiments that make up the artillery arm of the British Army. The Royal Regiment of Artillery comprises t ...
and
Royal Navy
The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
. This committee worked four years, between 1861 and 1865, during which time it formulated the best performing armor with the metallurgy as then known, suggested ways for improving its production and quality and helped develop more effective shot against ironclad vessels.
For instance, two processes were used in constructing iron armor. In the first, hammering, large lumps of iron of scrap or puddled iron were heated to welding temperature and placed under heavy steel hammers. Repeated blows welded these lumps into one solid plate and shaped it to the required form and dimensions. Hammered iron plate was the armor used in the earliest ironclad vessels, including
HMS ''Warrior''. The second method, rolling, involved stacking iron lumps atop one another, heating them to welding temperature and passing them between two iron rollers to become one plate of the required size. Rolled iron was difficult to produce initially, as it required machinery of immense size and great power. However, when the Special Committee tested both types of plate in 1863, it found that rolled iron was superior to hammered due to greater uniformity in quality. The committee and iron manufacturers worked together on how to more easily produce rolled plate, which became standard use in warships beginning in 1865.
The committee addressed the use of wooden backing with iron armor. Early European iron armour consisted of between four and five inches (roughly 10 to 13 cm) of wrought iron backed by between 18 and 36 inches (roughly one-half to one metre) of solid
wood
Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...
. After considerable testing, the committee found that wood prevented
spall
Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ba ...
ing, cushioned the shock of a hit from damaging the structure of the ship and distributed the force over a larger area, which prevented penetration. The drawback of using wood and iron was extreme weight. Experiments with reducing or eliminating wooden backing to save weight proved unsuccessful. The committee also tested steel as potential armor as its members felt that the harder the armor, the better it might deflect or resist shot. However, the steel being produced at that time proved too brittle to be effective. Iron, being softer, bent, dented and distorted but held together and remained an effective means of protection.
[Baxter, p. 202-3; Fairbairn, pp. 356-8; Osborne, pp. 32-3; Sandler, p. 53.]
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.
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 is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...
plates to the front face of iron armour. Efforts to carry out these proposals failed for many reasons, primarily because the
metallurgy
Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys.
Metallurgy encompasses both the ...
at the time was not up to the task.
By the mid-to-late 1870s, iron armour started to give way to
steel armour, which promised to reduce the thickness, and therefore the weight, of the armour.
References
Gene Slover's US Navy pages, Naval ordnance and gunnery, chapter XII. Armor retrieved 13 June 2006
Fairbairn, William et al, ''The Life of Sir William Fairbairn, BART'' (London: Longmans, Green and Company, 1877), ed. Pole, William FRS. At Google Books. Accessed 13 April 2012.
{{Naval armour
Naval armour