Ironclad warship

An ironclad was a steam-propelled warship of the later 19th century, protected by iron or steel armor plates. [Hill, Richard. "War at Sea in the Ironclad Age" ISBN 0-304-35273-X; p.17]

The ironclad was developed as a result of the vulnerability of wooden warships to explosive or incendiary shells. The first ironclad battleship, "La Gloire", was launched by the French Navy in 1859; [Sondhaus, Lawrence. "Naval Warfare 1815–1914" ISBN 0-415-21478-5. pp73–4] she prompted the British Royal Navy to start building ironclads. After the first clashes of ironclads took place during the American Civil War, it became clear that the ironclad had replaced the unarmored line-of-battle ship as the most powerful warship afloat. [Sondhaus, p. 86]

Ironclads were designed for several roles, including as high seas battleships, coastal defense ships, and long-range cruisers. The rapid evolution of warship design in the late 19th century transformed the ironclad from a wooden-hulled vessel which carried sails to supplement its steam engines into the steel-built, turreted battleships and cruisers familiar in the 20th century. This change was pushed forward by the development of heavier naval guns (the ironclads of the 1880s carried some of the heaviest guns ever mounted at sea)Fact|date=April 2008, more sophisticated steam engines, and advances in metallurgy which made steel shipbuilding possible.

The rapid pace of change in the ironclad period meant that many ships were obsolete as soon as they were complete, and that naval tactics were in a state of flux. Many ironclads were built to make use of the ram or the torpedo, which a number of naval designers considered the crucial weapons of naval combat. There is no clear end to the ironclad period, but towards the end of the 1890s the term "ironclad" dropped out of use. New ships were increasingly constructed to a standard pattern and designated battleships or armored cruisers.

Before the Ironclad

The ironclad became technically feasible and tactically necessary because of developments in shipbuilding in the first half of the 19th century. According to naval historian R.D. Hill:

Each of these developments was introduced separately in the decade before the first ironclads.

team propulsion

In the 18th and early 19th centuries fleets had relied on two types of major warship, the ship of the line and the frigate. The first major change to these types was the introduction of steam power for propulsion. While paddle steamer warships had been used from the 1830s onwards, steam propulsion only became suitable for major warships after the adoption of the screw propellor in the 1840s.Lambert, A. "The Screw Propellor Warship", in Gardiner "Steam, Steel and Shellfire" p.30–44 ]

Steam-powered screw frigates were built in the mid-1840s, and at the end of the decade the French Navy introduced steam power to its line of battle. The desire for change came from the ambition of Napoleon III to gain greater influence in Europe, which required a challenge to the British at sea. [Sondhaus, pp.37–41; Hill, p.25] The first purpose-built steam battleship was the 90-gun "Le Napoléon" in 1850. "Le Napoléon" was armed as a conventional ship-of-the-line, but her steam engines could give her a speed of 12 knots (22 km/h), regardless of the wind conditions: a potentially decisive advantage in a naval engagement.

The introduction of the steam ship-of-the-line led to a building competition between France and Britain. Eight sister-ships to "Le Napoléon" were built in France over a period of ten years, but the United Kingdom soon managed to take the lead in production. Altogether, France built ten new wooden steam battleships and converted 28 from older ships of the line, while the United Kingdom built 18 and converted 41.

Explosive shells

The era of the wooden steam ship-of-the-line was brief, because of new, more powerful naval guns. In the 1820s and 1830s, warships began to mount increasingly heavy guns, replacing 18-pounder guns with 32-, 36- or even 42-pounders on sailing ships and introducing 68-pounders on steamers. At the same time, the first shell guns firing explosive shells were introduced following their development by the French Général Henri-Joseph Paixhans, and by the 1840s were part of the standard armament for naval powers including the French Navy, British Royal Navy, Imperial Russian Navy and United States Navy. It is often held that the power of explosive shells to smash wooden hulls, as demonstrated by the Russian destruction of a Turkish squadron at the Battle of Sinope, spelled the end of the wooden-hulled warship. [Sondhaus, p.58] The more practical threat to wooden ships was from conventional cannon firing red-hot shot, which could lodge in the hull of a wooden ship and cause a fire or ammunition explosion. Some navies even experimented with hollow shot filled with molten metal for extra incendiary power.Lambert, A. "Battleships in Transition", Conway Maritime Press, London, 1984. ISBN 0-85177-315-X. p.94–5]

Iron armor

In the 1850s, the British and French navies deployed iron-armored floating batteries as a supplement to the wooden steam battlefleet in the Crimean War. The role of the battery was to assist unarmored mortar and gunboats bombarding shore fortifications. The French used three of their ironclad batteries ("Lave", "Tonnante" and "Dévastation") in 1855 against the defenses at the Battle of Kinburn (1855) on the Black Sea, where they were effective against Russian shore defences. They would later be used again during the Italian war in the Adriatic in 1859. [ [http://dossiersmarine.free.fr/fs_b_B1.html Source] ] The British plan to use theirs in the Baltic Sea against Kronstadt was influential in causing the Russians to sue for peace.Lambert A. "Iron Hulls and Armour Plate"; Gardiner "Steam, Steel and Shellfire" p. 47–55]

The batteries have a claim to the title of the first ironclad warships [Hill, p.17] but they were capable of only 4 knots (7 km/h) under their own power and were towed into action, [Sondhaus, p.61] and were marginal to the work of the navy. The brief success of the floating ironclad batteries convinced France to begin work on armored warships for their battlefleet.

Early Ironclad ships and battles

By the end of the 1850s it was clear that France was unable to match British building of steam warships, and to regain the strategic initiative a dramatic change was required. The result was the first ocean-going ironclad, the "La Gloire", begun in 1857 and launched in 1859. [Sondhaus, p.73–4]

"La Gloire"'s wooden hull was modelled on that of a steam ship of the line, reduced to one deck, sheathed in iron plates 4.5 inches (110 mm) thick. She was propelled by a steam engine, driving a single screw propeller for a speed 13 knots (24 km/h). She was armed with thirty-six convert|6.4|in|mm|sing=on rifled guns. France proceeded to construct 16 ironclad warships, including two more sister ships to "La Gloire", and the only two-decked broadside ironclads ever built, "Magenta" and "Solferino". [Sondhaus, p.74]

The Royal Navy had not been keen to sacrifice their advantage in steam ships of the line, but was determined that the first British iron ship would outmatch the French ships in every respect, particularly speed. A fast ship would have the advantage of being able to choose a range of engagement which could make her invulnerable to enemy fire. The British specification was more a large, powerful frigate than a ship-of-the-line. The requirement for speed meant a very long vessel, which had to be built from iron. The resulting vessel was "Warrior", built and launched in 1860. "Warrior" was a successful design; her weapons and armor were more effective than that of "La Gloire", and with the largest set of steam engines yet fitted to a ship she could steam at 14.3 knots (26.5 km/h).

By 1862, navies across Europe had adopted ironclads. Britain and France each had sixteen either completed or under construction, though the British vessels were larger. Austria, Italy, Russia, and Spain were also building ironclads. [Sondhaus, p.76] However, the first battles using the new ironclad ships involved neither Britain nor France, and involved ships markedly different from the broadside-firing, masted designs of "La Gloire" and "Warrior". The use of ironclads by both sides in the American Civil War, and the clash of the Italian and Austrian fleets at the Battle of Lissa, had an important influence on the development of ironclad design.

First battles between ironclads: The U.S. Civil War

The first use of ironclads in action came in the U.S. Civil War. The U.S. Navy at the time the war broke out had no ironclads, its most powerful ships being six steam-powered unarmoured frigates. [Sondhaus, p.77] Since the bulk of the Navy remained loyal to the Union, the Confederacy sought to gain advantage in the naval conflict by acquiring modern armored ships. The Confederate Congress voted $2 million in May 1861 to buy ironclads from overseas, and in July and August started work on construction and converting wooden ships.Still, William "The American Civil War" in Gardiner "Steam, Steel and Shellfire"]

On 12 October 1861, the CSS "Manassas", the CSS "Louisiana", and the CSS "Mississippi" became the first ironclads to enter battle, when they fought Union warships on the Mississippi. They were all built in New Orleans for river and coastal fighting. In February 1862, the even larger CSS "Virginia" joined the Confederate Navy, having been built at Norfolk. By this time the Union had completed seven ironclad gunboats of the "City" class, and was about to complete the USS "Monitor", an innovative design proposed by the Swedish inventor John Ericsson. The Union was also building a large armored frigate, the USS "New Ironsides", and the smaller USS "Galena". [Sondhaus, p.78]

The first battle between ironclads happened on 9 March 1862, as the "Monitor" was deployed to protect the Union's wooden fleet from the "Virginia" and other Confederate warships. In this engagement, named the Battle of Hampton Roads, the two ironclads repeatedly tried to ram one another while shells bounced off their armor. The battle attracted attention worldwide, making it clear that the wooden warship was now out of date with the ironclads destroying them easily. [Sondhaus, p 78–81]

The Civil War saw more ironclads built by both sides, and they played an increasing role in the naval war alongside the unarmored warships, commerce raiders and blockade runners. The Union built a large fleet of fifty monitors modelled on their namesake. The Confederacy built ships designed as smaller versions of the "Virginia" ("Merrimack"), of which all saw action, [Sondhaus, p82] but their attempts to buy ironclads overseas were frustrated as European nations confiscated ships being built for the Confederacy — especially in Russia, the only country to openly support the Union through the war. Only CSS "Stonewall" was completed, the only other non Russian ironclad to be completed over seas, and she arrived in American waters just in time for the Battle of Galveston. [Sondhaus, p.85]

Through the remainder of the war, ironclads saw action in the Union's attacks on Southern ports. Seven Union monitors, including USS "Montauk", as well as two other ironclads, the ironclad frigate "New Ironsides" and a light-draft "Keokuk", participated in the failed attack on Charleston; one was sunk. Two small ironclads, CSS "Palmetto State" and CSS "Chicora" and two large ironclads, CSS "Shenandoah" and CSS "Raleigh" participated in the defence of the harbor. For the later attack at Mobile Bay, the Union assembled four monitors as well as 11 wooden ships, facing the CSS "Tennessee", the Confederacy's most powerful ironclad and the CSS "Mobile", CSS "Montgomery", CSS "Peach State", and CSS "Arizona". [Sondhaus, p.81]

Lissa: First Ironclad fleet battle

The first fleet battle, and the first ocean battle, involving ironclad warships was the Battle of Lissa in 1866. Waged between the Austro-Hungarian and Italian navies, the battle pitted combined fleets of wooden frigates and corvettes and ironclad warships on both sides in the largest naval battle between Navarino and Tsushima. [Sondhaus, p.94–96]

The Italian fleet consisted of 12 ironclads and a similar number of wooden warships, escorting transports which carried troops intending to land on the Adriatic island of Lissa. Among the Italian ironclads were seven broadside ironclad frigates, four smaller ironclads, and the newly-built "Affondatore" – a double-turretted ram. Opposing them, the Austrian navy had seven ironclad frigates. [Sondhaus, p.94–96]

The Austrians believed their ships to have less effective guns than their enemy, so decided to engage the Italians at close range and ram the enemy. The Austrian fleet formed into an arrowhead formation with the ironclads in the first line, charging at the Italian ironclad squadron. In the melee which followed both sides were frustrated by the lack of damage inflicted by guns, and by the difficulty of ramming—nonetheless, the effective ramming attack being made by the Austrian flagship against the Italian attracted great attention in following years. [Sondhaus, p.94–96]

The superior Italian fleet lost its two ironclads, "Re d'Italia" and "Palestro", while the Austrian unarmoured screw two-decker "Kaiser" remarkably survived close actions with four Italian ironclads. The battle ensured the popularity of the ram as a weapon in European ironclads for many years, and the victory won by Austria-Hungary established it briefly as the predominant naval power in the Adriatic. [Sondhaus, p.94–96]

The battles of the American Civil War and at Lissa were very influential on the designs and tactics of the ironclad fleets that followed. In particular, it taught a generation of naval officers the misleading lesson that ramming was the best way to sink enemy ironclads.

Armament and tactics

The adoption of iron armor meant that the traditional naval armament of dozens of light cannon became useless, since their shot would bounce off an armored hull. To penetrate armor, increasingly heavy guns were mounted on ships; nevertheless, the view that ramming was the only way to sink an ironclad became widespread. The increasing size and weight of guns also meant a movement away from the ships mounting many guns broadside, in the manner of a ship-of-the-line, towards a handful of guns in turrets for all-round fire.

Ram craze

was again the most important weapon in naval warfare. With steam power freeing ships from the wind, and armor making them invulnerable to shellfire, the ram seemed to offer the opportunity to strike a decisive blow.

The scant damage inflicted by the guns of "Monitor" and "Virginia" at Battle of Hampton Roads and the spectacular but lucky success of the Austrian flagship "Ferdinand Max" sinking the Italian "Re d'Italia" at Lissa gave strength to the ramming craze. [Hill, p35] From the early 1870s to early 1880s most British naval officers thought that guns were about to be replaced as the main naval armament by the ram. Those who noted the tiny number of ships sunk by ramming attacks struggled to be heard.Beeler, J. "Birth of the Battleship: British Capital Ship Design, 1870–1881". London, Caxton, 2003. ISBN 1-84067-5349 p.106–7]

The revival of ramming had a significant effect on naval tactics. Since the 17th century the predominant tactic of naval warfare had been the line of battle, where a fleet formed a long line to give it the best fire from its broadside guns. This tactic was totally unsuited to ramming, and the ram threw fleet tactics into disarray. The question of how an ironclad fleet should deploy in battle to make best use of the ram was never tested in battle, and if it had been, combat might have shown that rams could only be used against ships which were already stopped dead in the water. [Beeler, p.107]

The ram finally fell out of favour in the 1880s, as the same effect could be achieved with a torpedo, with less vulnerability to quick-firing guns. [Beeler, p.146]

Development of naval guns

The armament of ironclads tended to become concentrated in a small number of powerful guns capable of penetrating the armor of enemy ships at range; calibre and weight of guns increased markedly to achieve greater penetration. Throughout the ironclad era navies also grappled with the complexities of rifled versus smoothbore guns and breech-loading versus muzzle-loading.

HMS "Warrior" carried a mixture of 110-pounder or 7 inch (180 mm) breech-loading rifles and more traditional 68–pounder smoothbore guns. "Warrior" highlighted the challenges of picking the right armament; the breech-loaders she carried, designed by Sir William Armstrong, were intended to be the next generation of heavy armament for the Royal Navy, but were shortly withdrawn from service. [Beeler, p.71]

Breech-loading guns seemed to offer important advantages. A breech-loader could be reloaded without moving the gun, a lengthy process particularly if the gun then needed to be re-aimed. The "Warrior"'s Armstrong guns also had the virtue of being lighter than an equivalent smoothbore and, due to their rifling, more accurate. [Beeler, p.71] Nonetheless, the design was rejected because of problems which plagued breech-loaders for decades.

The weakness of the breech-loader was the obvious problem of sealing the breech. All guns are powered by the explosive conversion of gunpowder into gas. This explosion propels the shot or shell out of the front of the gun, but also imposes great stresses on the gun-barrel. If the breech—which experiences some of the greatest forces in the gun—is not entirely secure, then there is a risk that either gas will discharge through the breech or that the breech will break. This in turn reduces the muzzle velocity of the weapon and can also endanger the gun crew. The "Warrior"'s Armstrong guns suffered from both problems; the shells were unable to penetrate the 4.5 in (118 mm) armor of "La Gloire", while sometimes the screw which closed the breech flew backwards out of the gun on firing. Similar problems were experienced with the breech-loading guns which became standard in the French and German navies. [Beeler, p.72–3]

These problems influenced the British to equip ships with muzzle-loading weapons of increasing power until the 1880s. After a brief introduction of 100-pounder or 9.5-inch (240 mm) smoothbore Somerset Gun, which weighed 6.5 tons (6.6 t), the Admiralty introduced 7-inch (178 mm) rifled guns, weighing 7 tons. These were followed by a series of increasingly mammoth weapons—guns weighing 12, 25, 25, 38 and finally 81 tons, with calibre increasing from 8-inch (203 mm) to 16-inch (406 mm).

The decision to retain muzzle-loaders until the 1880s has been criticised by historians. However, at least until the late 1870s, the British muzzle-loaders had superior performance in terms of both range and rate of fire than the French and Prussian breech-loaders, which suffered from the same problems as had the first Armstrong guns. [Beeler, p73–5]

From 1875 onwards, the balance between breech- and muzzle-loading changed. The aptly named Captain de Bange invented a method of reliably sealing a breech, adopted by the French in 1873. Just as compellingly, the growing size of naval guns made muzzle-loading much more complicated. With guns of such size there was no prospect of hauling in the gun for re-loading, or even re-loading by hand, and complicated hydraulic systems were required for re-loading the gun outside the turret without exposing the crew to enemy fire. In 1882, the 81-ton guns of HMS "Inflexible" fired only once every 11 minutes while bombarding Alexandria during the Urabi Revolt. [Beeler, p.77–8] The 450 mm (17.72 inch) guns of "Duilio" could each fire a round every 15 minutes. [Brown, D.K. "The Era of Uncertainty", in "Steam Steel and Shellfire", p.85] .

In the Royal Navy, the switch to breech-loaders was finally made in 1879; as well as the significant advantages in terms of performance, opinion was swayed by an explosion on board HMS "Thunderer" caused by a gun being double-loaded, a problem which could only happen with a muzzle-loading gun. Roberts, J "Warships of Steel 1879–1889" in Gardiner "Steam, Steel and Shellfire"]

The calibre and weight of guns could only increase so far. The larger the gun, the slower it would be to load, the greater the stresses on the ship's hull, and the less the stability of the ship. The size of the gun peaked in the 1880s, with some of the heaviest calibres of gun ever used at sea. HMS "Benbow" carried two 16.25-inch (413 mm) guns, each weighing 110 tons—no British battleship would ever carry guns as large. The Italian 450 mm (17.72 inch) guns would be larger than any gun fitted to a battleship until the 18-inch (457 mm) armament of the Japanese "Yamato" class of World War II. [The Royal Navy did build convert|18|in|mm|sing=on guns for the "Furious" class battlecruisers, though these ships were finished as aircraft carriers and their guns eventually fitted to the Lord Clive class monitor, seeing service in World War I.]

Another method of increasing firepower was to vary the projectile fired or the nature of the propellant. Early ironclads used black powder, which expanded rapidly after combustion; this meant cannons had relatively short barrels, to prevent the barrel itself slowing the shell. The sharpness of the black powder explosion also meant that guns were subjected to extreme stress. One important step was to press the powder into pellets, allowing a slower, more controlled explosion and a longer barrel. A further step forward was the introduction of chemically different "brown powder" which combusted more slowly again. It also put less stress on the insides of the barrel, allowing guns to last longer and to be manufactured to tighter tolerances.Campbell, J "Naval Armaments and Armour" in Gardiner "Steam, Steel and Shellfire", p.158–169]

The development of smokeless powder, based on nitroglycerine or nitrocellulose, by the French inventor Paul Vielle in 1884 was a further step allowing smaller charges of propellant with longer barrels. The guns of the pre-Dreadnought battleships of the 1890s tended to be smaller in calibre compared to the ships of the 1880s, most often 12 in (305 mm), but progressively grew in length or barrel, making use of improved propellants to gain greater muzzle velocity.

The nature of the projectiles also changed during the ironclad period. Initially, the best armor-piercing projectile was a solid cast-iron shot. Later, shot of chilled iron, a harder iron alloy, gave better armor-piercing qualities. Eventually the armor-piercing shell was developed.

Positioning of armament

Broadside ironclads

The first British, French and Russian ironclads, in a logical development of warship design from the long preceding era of wooden ships of the line, carried their weapons in a single line along their sides and so were called "broadside ironclads." Both "La Gloire" and HMS "Warrior" were examples of this type. Because their armor was so heavy, they could only carry a single row of guns along the main deck on each side rather than a row on each deck. [Sondhaus, p73–4]

A significant number of broadside ironclads were built in the 1860s, principally in Britain and France, but in smaller numbers by other powers including Italy, Austria, Russia and the United States. The advantages of mounting guns on both broadsides was that the ship could engage more than one adversary at a time, and the rigging did not impede the field of fire. [Beeler, p.91–93]

Broadside armament also had disadvantages, which became more serious as ironclad technology developed. Heavier guns to penetrate ever-thicker armor meant that fewer guns could be carried, and so it was important that every gun could be brought to bear. Furthermore, the adoption of ramming as an important tactic meant the need for ahead and all-round fire. [Noel, Gerard H U et al, "The Gun, Ram and Torpedo, Manoeuvres and tactics of a Naval Battle of the Present Day", 2nd Edition, pub Griffin 1885.] These problems led to broadside designs being superseded by designs that gave greater all-round fire, which included central-battery, turret, and barbette designs. [Beeler, p.91–93]

Turrets, batteries and barbettes

There were two main alternatives to the broadside. In one design, the guns were placed in an armoured casemate amidships: this arrangement was called the 'box-battery' or 'centre-battery'. In the other, the guns could be placed on a rotating platform to give them a broad field of fire; when fully armored, this arrangement was a turret and when partially or unarmored a barbette.

The centre-battery was the simpler and, during the 1860s and 1870s, the more popular method. Concentrating guns amidships meant the ship could be shorter and handier than a broadside type. The first full-scale centre-battery ship was HMS "Bellerophon" of 1865; the French laid down centre-battery ironclads in 1865 which were not completed until 1870. Centre-battery ships often, but not always, had a recessed freeboard enabling some of their guns to fire directly ahead. [Sondhaus, p.87]

The turret made its debut with USS "Monitor" in 1862, with a type of turret designed by the Swedish engineer John Ericsson. A competing turret design was proposed by the British inventor Cowper Coles. Ericsson's turret turned on a central spindle, and Coles's turned on a ring of bearings. Turrets offered the maximum arc of fire from the guns, but there were significant problems with their use in the 1860s. The fire arc of a turret would be considerably limited by masts and rigging, so they were unsuited to use on the earlier ocean-going ironclads. The second problem was that turrets were extremely heavy—unless a ship was very large, the weight of the turrets meant a ship needed a low freeboard or would suffer from stability problems. [Beeler, p.92–3] HMS "Captain", designed by Coles as an example of how this circle could be squared, capsized in 1870. Her half-sister "Monarch" was restricted to firing from her turrets only on the port and starboard beams. The third Royal Navy ship to combine turrets and masts was HMS "Inflexible" of 1876, which carried two turrets on either side of the centre-line, allowing both to fire fore, aft and broadside. [Beeler, p.122]

A lighter alternative to the turret, particularly popular with the French navy, was the barbette. These were fixed armored towers which held a gun on a turntable; the gun was often on a 'disappearing mount' which carried it entirely into the barbette for loading and out for firing. The crew was sheltered from direct fire, but vulnerable to plunging fire, for instance from shore emplacements. The barbette was lighter than the turret, needing less machinery and no roof armor—though nevertheless some barbettes were stripped of their armor plate to reduce the top-weight of their ships. The barbette became widely adopted in the 1880s, and with the addition of an armored 'gun-house', transformed into the turrets of the pre-Dreadnought battleships.

Torpedos

The ironclad age saw the development of explosive torpedos as naval weapons, which helped complicate the design and tactics of ironclad fleets. The first torpedoes were static mines, used with dubious efficiency in the American Civil War. That conflict also saw the development of the spar torpedo, an explosive charge pushed against the hull of a warship by a small boat. For the first time, a large warship faced a serious threat from a smaller one—and given the relative inefficiency of shellfire against ironclads, the threat from the spar torpedo was taken seriously. The U.S. Navy converted four of its monitors to become turretless armored spar-torpedo vessels while under construction in 1864–5, but these vessels never saw action. [Sondhaus, p.83] Another proposal, the towed or 'Harvey' torpedo, involved an explosive on a line or outrigger; either to deter a ship from ramming or to make a torpedo attack by a boat less suicidal.

A more practical and influential weapon was the self-propelled or 'Whitehead' torpedo. Invented in 1868 and deployed in the 1870s, the Whitehead torpedo formed part of the armament of ironclads of the 1880s like HMS "Inflexible" and the Italian "Duilio" and "Dandolo". The ironclad's vulnerability to the torpedo was a key part of the critique of armored warships made by the Jeune Ecole school of naval thought; it appeared that any ship armored enough to prevent destruction by gunfire would be slow enough to be easily caught by torpedo. In practice, however, the Jeune Ecole was only briefly influential and the torpedo formed part of the confusing mixture of weapons possessed by ironclads. [Sondhaus, p.156]

Ironclad armor and construction

The first ironclads were built on wooden or iron hulls, and protected by wrought iron armor backed by thick wooden planking. Ironclads were still being built with wooden hulls into the 1870s, and this was only in part due to the relative cost and scarcity of iron.

Hulls: Iron, wood and steel

Using iron construction for warships offered advantages for the engineering of the hull. However, unarmored iron had many military disadvantages, and offered technical problems which kept wooden hulls in use for many years, particularly for long-range cruising warships.

Iron ships had first been proposed for military use in the 1820s. In the 1830s and 1840s France, Britain and the USA had all experimented with iron-hulled but unarmored gunboats and frigates. However, the iron-hulled frigate was abandoned by the end of the 1840s, because iron hulls were more vulnerable to solid shot; iron was more brittle than wood, and iron frames more likely to fall out of shape than wood. [Lambert "Battleships in Transition", p.19]

The unsuitability of unarmored iron for warship hulls meant that iron was only adopted as a building material for battleships when protected by armor. However, iron gave the naval architect many advantages. Iron allowed larger ships and more flexible design, for instance the use of watertight bulkheads on the lower decks. "Warrior", built of iron, was longer and faster than the wooden-hulled "La Gloire". Iron could be produced to order and used immediately, in contrast to the need to give wood a long period of seasoning. And, given the large quantities of wood required to build a steam warship and the falling cost of iron, iron hulls were increasingly cost-effective. The main reason for the French use of wooden hulls for the ironclad fleet built in the 1860s was that the French iron industry could not supply enough, and the main reason why Britain built its handful of wooden-hulled ironclads was to make best use of hulls already started and wood already bought. [Beeler, p. 30–36]

Wooden hulls continued to be used for long-range and smaller ironclads, because iron nevertheless had a significant disadvantage. Iron hulls suffered quick fouling by marine life, slowing the ships down—manageable for a European battlefleet close to dry docks, but a difficulty for long-range ships. The only solution was to sheath the iron hull first in wood and then in copper, a laborious and expensive process which made wooden construction remain attractive. [Beeler, p.32–3] Iron and wood were to some extent interchangeable: the Japanese "Kongo" and "Hiei" ordered in 1875 were sister-ships, but one was built of iron and the other of composite construction. [Jenschura Jung & Mickel, "Warships of the Imperial Japanese Navy", ISBN 0-85368-151-1]

After 1872, steel started to be introduced as a material for construction. Compared to iron, steel allows for greater structural strength for a lower weight. The French Navy led the way with the use of steel in its fleet, starting with the "Redoutable", laid down in 1873 and launched in 1876. [Gardiner, "Steam, Steel and Shellfire", p.96] Redoutable nonetheless had wrought iron armor plate, and part of her exterior hull was iron rather than steel.

Even though Britain led the world in steel production, the Royal Navy was slow to adopt steel warships. The Bessemer process for steel manufacture produced too many imperfections for large-scale use on ships. French manufacturers used the Siemens-Martin process to produce adequate steel, but British technology lagged behind. [Beeler, p.37–41] The first all-steel warships built by the Royal Navy were the dispatch vessels "Iris" and "Mercury", laid down in 1875 and 1876.

Armor and protection schemes

Iron-built ships used wood as part of their protection scheme. HMS "Warrior" was protected by 4.5 in (114 mm) of wrought iron backed by 15 in (381 mm) of teak, the strongest shipbuilding wood. The wood played two roles, preventing spalling and also preventing the shock of a hit damaging the structure of the ship. Later, wood and iron were combined in 'sandwich' armor, for instance in HMS "Inflexible". [Hill, p.39]

Steel was also an obvious material for armor. It was tested in the 1860s, but the steel of the time was too brittle and disintegrated when struck by shells. Steel became practical to use when a way was found to fuse steel onto wrought iron plates, giving a form of compound armor. This compound armor was used by the British in ships built from the late 1870s, first for turret armor (starting with HMS "Inflexible") and then for all armor (starting with "Colossus" of 1882). [Beeler, p.45] The French and German navies adopted the innovation almost immediately, with licenses being given for the use of the 'Wilson System' of producing fused armor. [Sondhaus, p.164–5]

The first ironclads to have all-steel armor were the Italian "Duilio" and "Dandolo". Though the ships were laid down in 1873 their armor was not purchased from France until 1877. The French navy decided in 1880 to adopt compound armor for its fleet, but found it limited in supply, so from 1884 the French navy was using steel armor. [Sondhaus, p164–5] Britain stuck to compound armor until 1889.

The ultimate ironclad armor was case hardened nickel-steel. In 1890, the U.S. Navy tested steel armor hardened by the Harvey process and found it superior to compound armor. For several years 'Harvey steel' was the state of the art, produced in the U.S., France, Germany, Britain, Austria and Italy. In 1894, the German firm Krupp developed gas cementing, which further hardened steel armor. The German "Kaiser Friedrich III", laid down in 1895, was the first ship to benefit from the new 'Krupp armor' and the new armor was quickly adopted; the Royal Navy using it from HMS "Canopus", laid down in 1896. By 1901 almost all new battleships used Krupp armor, though the U.S. continued to use Harvey armor alongside until the end of the decade.

The equivalent strengths of the different armor plates was as follows: 15 in (381 mm) of wrought iron was equivalent to 12 in (305 mm) of either plain steel or compound iron and steel armor, and to 7.75 in (197 mm) of Harvey armor or 5.75 in (146 mm) of Krupp armor. [Sondhaus, p.166]

Ironclad construction also prefigured the later debate in battleship design between tapering and 'all-or-nothing' armour design. "Warrior" was only semi-armoured, and could have been disabled by hits on the bow and stern. [Reed "Our Iron Clad Ships", p45–47.] As the thickness of armor grew to protect ships from the increasingly heavy guns, the area of the ship which could be fully protected diminished. "Inflexible"'s armor protection was largely limited to the central citadel amidships, protecting boilers and engines, turrets and magazines, and little else. An ingenious arrangement of cork-filled compartments and watertight bulkheads was intended to keep her stable and afloat in the event of heavy damage to her un-armored sections. [Beeler, p 133–4]

Propulsion: Steam and sail

The first ocean-going ironclads carried masts and sails like their wooden predecessors, and these features were only gradually abandoned. Early steam engines were inefficient; the wooden steam fleet of the Royal Navy could only carry "5 to 9 days coal", [Beeler, p.54] and the situation was similar with the early ironclads. "Warrior" also illustrates two design features which aided hybrid propulsion; she had retractable screws to reduce drag while under sail (though in practice the steam engine was run at a low throttle), and a telescopic funnel which could be folded down to the deck level. [Hill, p.44]

Ships designed for coastal warfare, like the floating batteries of the Crimea, or USS "Monitor" and her sisters, dispensed with masts from the beginning. The British HMS Devastation, started in 1869, was the first large, ocean-going ironclad to dispense with masts. Her principal role was for combat in the English Channel and other European waters; and while her coal supplies gave her enough range to cross the Atlantic, she would have had little endurance on the other side of the ocean. The "Devastation" and the similar ships commissioned by the British and Russian navies in the 1870s were the exception rather than the rule. Most ironclads of the 1870s retained masts, and only the Italian navy, which during that decade was focused on short-range operations in the Adriatic, [Sondhaus, p111–2] built consistently mastless ironclads. [Beeler, p.63–4]

During the 1860s, steam engines improved with the adoption of double-expansion steam engines, which used 30–40% less coal than earlier models. The Royal Navy decided to switch to the double-expansion engine in 1871, and by 1875 they were widespread. However, this development alone was not enough to herald the end of the mast. Whether this was due to a conservative desire to retain sails, or was a rational response to the operational and strategic situation, is a matter of debate. A steam-only fleet would require a network of coaling stations worldwide, which would need to be fortified at great expense to stop them falling into enemy hands. Just as significantly, because of unsolved problems with the technology of the boilers which provided steam for the engines, the performance of double-expansion engines was rarely as good in practice as it was in theory. [Beeler, p.57–62]

During the 1870s the distinction grew between 'first-class ironclads' or 'battleships' on the one hand, and 'cruising ironclads' designed for long-range work on the other. The demands on first-class ironclads for very heavy armor and armament meant increasing displacement, which reduced speed under sail; and the fashion for turrets and barbettes made a sailing rig increasingly inconvenient. HMS "Inflexible", launched in 1876 but not commissioned until 1881, was the last British battleship to carry masts, and these were widely seen as a mistake. The start of the 1880s saw the end of sailing rig on ironclad battleships. [Beeler, p.54]

Sails persisted on 'cruising ironclads' for much longer. During the 1860s the French navy had produced the "Alma" and "La Galissoniere" classes as small, long-range ironclads as overseas cruisers [Sondhaus, p.88] and the British had responded with ships like "Swiftsure" of 1870. The Russian ship "General Admiral", laid down in 1870 and completed in 1875, was a model of a fast, long-range ironclad which was likely to be able to out-run and out-fight ships like "Swiftsure". Even the later HMS "Shannon", often described as the first British armored cruiser, would have been too slow to outrun "General Admiral". While "Shannon" was the last British ship with a retractable propellor, later armored cruisers of the 1870s retained sailing rig, sacrificing speed under steam in consequence. It took until 1881 for the Royal Navy to lay down a long-range armored warship capable of catching enemy commerce raiders, "Warspite", which was completed in 1888. [Beeler, p.194] While sailing rigs were obsolescent for all purposes by the end of the 1880s, rigged ships were in service until the early years of the 20th century.

The final evolution of ironclad propulsion was the adoption of the triple-expansion steam engine, a further refinement which was first adopted in HMS "Sans Pareil", laid down in 1885 and commissioned in 1891. Many ships also used a forced draught to get additional power from their engines, and this system was widely used until the introduction of the steam turbine in the mid-1900s.Griffiths, D "Warship Machinery" in Gardiner "Steam, Steel and Shellfire"]

Ironclad fleets

While ironclads spread rapidly in navies worldwide, there were few pitched naval battles involving ironclads. Most European nations settled differences on land, and the Royal Navy dominated the sea to such an extent that no rival power could take Britain on. The naval engagements involving ironclads normally involved colonial actions or clashes between second-rate naval powers.

There were many types of ironclads: [Conway "All the World's Fighting Ships 1860–1905", published Conway Maritime Press, 1979. ISBN 0-8317-0302-4]
* Sea-going ships intended to "stand in the line of battle"; the precursors of the battleship. [This term was still in use in the 1860s and 70s for what we would now call 'battleships'. See, for example: Noel, Gerard H U et al, "The Gun, Ram and Torpedo, Manoeuvres and tactics of a Naval Battle of the Present Day", 2nd Edition, pub Griffin 1885.]
* Coastal service and riverine vessels, including 'floating batteries' and 'monitors'
* Vessels intended for commerce raiding or protection of commerce, called 'armoured cruisers'

Navies

The United Kingdom possessed the largest navy in the world for the whole of the ironclad period. The Royal Navy was the second to adopt ironclad warships, and it applied them worldwide in their whole range of roles. In the age of sail, the British strategy for war depended on the Royal Navy mounting a blockade of the ports of the enemy. Because of the limited endurance of steamships, this was no longer possible, so the British planned to engage an enemy fleet in harbor as soon as war broke out. To this end, the Royal Navy developed a series of 'coast-assault battleships', starting with the "Devastation" class. These 'breastwork monitors' were markedly different from the other high-seas ironclads of the period and were an important precursor of the modern battleship. [Beeler, p.204] Through the 1860s and 1870s the Royal Navy was superior to its potential rivals, but in the early 1880s widespread concern about the threat from France and Germany culminated in the Naval Defence Act which promulgated the idea of a 'two-power standard', that Britain should possess as many ships as the next two navies combined. This standard provoked aggressive shipbuilding in the 1880s and 1890s.Kennedy, Paul M. "The Rise and Fall of British Naval Mastery", Macmillan, London, 1983. ISBN 0-333-35094, p.178–9]

British ships did not participate in any major wars in the ironclad period. The Royal Navy's ironclads only saw action as part of colonial battles or one-sided engagements like the bombardment of Alexandria in 1882. Defending British interests against Ahmed 'Urabi's Egyptian revolt, a British fleet opened fire on the fortifications around the port of Alexandria. A mixture of centre-battery and turret ships bombarded Egyptian positions for most of a day, forcing the Egyptians to retreat; return fire from Egyptian guns was heavy at first, but inflicted little damage, killing only five British sailors. [Hill, p.185]

The French navy built the first ironclad to try to gain a strategic advantage over the British, but were consistently out-built by the British. Despite taking the lead with a number of innovations like breech-loading weapons and steel construction, the French navy could never match the size of the Royal Navy. In the 1870s, the construction of ironclads ceased for a while in France as the Jeune Ecole school of naval thought took prominence, suggesting that torpedo boats and unarmored cruisers would be the future of warships. Like the British, the French navy saw little action with its ironclads; the French blockade of Germany in the Franco-Prussian War was ineffective, as the war was settled entirely on land. [Sondhaus, p.101]

Russia built a number of ironclads, generally copies of British or French designs. Nonetheless, there were real innovations from Russia; the first true type of ironclad armored cruiser, the "General Admiral" of the 1870s, and a set of remarkably badly-designed circular battleships referred to as 'popoffkas'. The Russian Navy pioneered the wide-scale use of torpedo boats during the Russo-Turkish War of 1877–1878, mainly out of necessity because of the superior numbers and quality of ironclads used by the Turkish navy. [Sondhaus, p.122–6] Russia expanded her navy in the 1880s and 1890s with modern armored cruisers and battleships, but the ships were let down by poor crews and leadership, resulting in the famous defeats by the Japanese in the Russo-Japanese War of 1904–1905. [Sondhaus, p.187–191]

The U.S. Navy ended the Civil War with about fifty monitor-type coastal ironclads; by the 1870s most of these were laid up in reserve, leaving the USA virtually without an ironclad fleet. Another five large monitors were ordered in the 1870s. The limitations of the monitor type effectively prevented the USA from projecting power overseas, and until the 1890s the USA would have come off badly in a conflict with even Spain or the Latin American powers. The 1890s saw the beginning of what became the Great White Fleet, and it was the modern pre-Dreadnoughts and armored cruisers built in the 1890s which defeated the Spanish fleet in the Spanish-American War of 1898. [Sondhaus, p126–8; p173–9]

Ironclads were widely used in South America. Both sides used ironclads in the Chincha Islands War between Spain and Chile and Peru in the early 1860s. The powerful Spanish "Numancia" participate on the Battle of Callao but was unable to inflict significative damage to the Callao defences. Besides, Peru was able to deploy two locally build ironclads based on American Civil War designs [Historia naval del Perú. Tomo IV, Valdizán Gamio, José] , the "Loa" (a wooden ship converted into a casamate ironclad) and the "Victoria" (an small monitor armed with a single 68 pdr gun), as well as two British-built ironclads; "Independencia", a centre-battery ship, and the turret ship "Huáscar". "Numancia" was the first ironclad to circumnavigate the world, arriving in Cádiz on 20 September 1867, and earning the motto: "Enloricata navis que primo terram circuivit"). In the War of the Pacific in 1879, both Peru and Chile had ironclad warships, including some of those used a few years previously against Spain. While the "Independencia" ran aground early on, the Peruvian ironclad "Huáscar" made a great impact against Chilean shipping, delaying chilean ground invasion by six months. She was eventually caught by two more modern Chilean centre-battery ironclads, the "Blanco Encalada" and the "Almirante Cochrane" at the Battle of Angamos Point. [Sondhaus p97–99, 127–132]

Ironclads were also used from the inception of the Imperial Japanese Navy. The "Kōtetsu" (Japanese: 甲鉄, literally "Ironclad", later renamed "Azuma" 東, "East") had a decisive role in the Naval Battle of Hakodate Bay in May 1869, which marked the end of the Boshin War, and the complete establishment of the Meiji Restoration. The IJN continued to develop its strength and commissioned a number of warships from British and European shipyards, first ironclads and later armored cruisers. These ships engaged the Chinese Beiyang fleet which was superior on paper at least at the Battle of the Yalu River. Thanks to superior short-range firepower, the Japanese fleet came off better, sinking or severely damaging eight ships and receiving serious damage to only four. The naval war was concluded the next year at the Battle of Weihaiwei, where the strongest remaining Chinese ships were surrendered to the Japanese. [Hill, p.191]

End of the ironclad

There is no clearly-defined end to the ironclad. Towards the end of the 19th century, the descriptions 'battleship' and 'armored cruiser' came to replace the term 'ironclad'. [Beeler, p.154 states that HMS "Edinburgh" (1882) was the first British capital ship to be routinely called a battleship.]

The proliferation of ironclad battleship designs came to an end in the 1890s as navies reached a consensus on the design of battleships, producing the type known as the pre-Dreadnought. These ships are sometimes covered in treatments of the ironclad warship. The next evolution of battleship design, the dreadnought, is never referred to as an 'ironclad'. [Hill, p.18]

Most of the ironclads of the 1870s and 1880s served into the first decade of the 20th century. A handful, for instance US navy monitors laid down in the 1870s, saw active service in World War I. Pre-Dreadnought battleships and cruisers of the 1890s saw widespread action in World War I and in some cases through to World War II.

Ironclads today

A number of ironclads have been preserved or reconstructed as museum ships.
*HMS "Warrior" is today a fully-restored museum ship in Portsmouth, England.
*"Huáscar" is berthed at the port of Talcahuano, on display for visitors.
*The City class ironclad USS|Cairo|1861|6 is currently on display in Vicksburg, Mississippi.
*The hulk of a breastwork monitor, the HMVS "Cerberus", survives in Melbourne, Australia.
*Northrop Grumman in Newport News constructed a full-scale replica of USS|Monitor. The replica was laid down in February, 2005 and completed just two months later. [Citation
last = Northrop Grumman Newport News
first =
title = Northrop Grumman Employees Reconstruct History with USS Monitor Replica
url=http://www.nn.northropgrumman.com/news/2005/050226_news.html
access-date = 2007-05-21] '
*The Japanese pre-Dreadnought "Mikasa" is a museum ship at Yokosuka.
*The Dutch Ramtorenschip (Coastal ram) "Buffel" is a museum ship at Rotterdam.
*The Dutch Ramtorenschip (Coastal ram) "Schorpioen" is a museum ship at Den Helder.
*CSS "Texas" portrayed in the movie Sahara (2005 film).

References

* Eugène M. Koleśnik, Roger Chesneau, N. J. M. Campbell. "Conway's All the World's Fighting Ships 1860–1905". Conway Maritime Press, 1979. ISBN 0-8317-0302-4
* Archibald, EHH (1984). "The Fighting Ship in the Royal Navy 1897–1984". Blandford. ISBN 0-7137-1348-8.
* Ballard, George, "The Black Battlefleet". Naval Institute Press, 1980. ISBN 0870219243
* Baxter, James Phinney III (1933), "The Introduction of the Ironclad Warship", Harvard University Press, 1933
* Beeler, John, "Birth of the Battleship: British Capital Ship Design 1870–1881". Caxton, London, 2003. ISBN 1-84067-5349
* Brown, DK (2003). "Warrior to Dreadnought: Warship Development 1860–1905". Caxton Editions. ISBN 1-84067-529-2.
*cite book
last =
first =
author = Gardiner, Robert and Lambert, Andrew
coauthors =
title = Steam, Steel and Shellfire: The Steam Warship, 1815–1905
publisher = Book Sales
year = 2001
pages =
id = ISBN 0-7858-1413-2
* Canney, Donald L "The Old Steam Navy, The Ironclads, 1842–1885". Naval Institute Press, 1993
* cite book
author= Greene, Jack and Massignani, Alessandro
title=Ironclads At War
publisher=Combined Publishing
year=1998
id=ISBN 0-938289-58-6
* Hill, Richard. War at Sea in the Ironclad Age ISBN 0-304-35273-X
* Jenschura Jung & Mickel, "Warships of the Imperial Japanese Navy 1869–1946", ISBN 0-85368-151-1
* Kennedy, Paul M. "The Rise and Fall of British Naval Mastery". Macmillan, London, 1983. ISBN 0-333-35094-4
* Lambert, Andrew "Battleships in Transition: The Creation of the Steam Battlefleet 1815–1860". Conway Maritime Press, London, 1984. ISBN 0-85177-315-X
* Noel, Gerard et al, "The Gun, Ram and Torpedo, Manoeuvres and tactics of a Naval Battle of the Present Day", 2nd Edition, pub. Griffin 1885
* Northrop Grumman Newport News, [http://www.nn.northropgrumman.com/news/2005/050226_news.html Northrop Grumman Employees Reconstruct History with USS Monitor Replica] . Retrieved on 2007-05-21
*Reed, Edward J "Our Ironclad Ships, their Qualities, Performance and Cost". John Murray, 1869.
* Sondhaus, Lawrence. "Naval Warfare 1815–1914". Routledge, London, 2001. ISBN 0-415-21478-5.
*Sandler, Stanley. "Emergence of the Modern Capital Ship" (Newark, DEL. Associated University Presses, 1979.

Notes

External links

* [http://www.klaus-kramer.de/Schiff/Panzerschiffe/Panzerschiffe_1/Panzerschiffe_1_engl_top.html The first ironclads 1859–1872, engravings]
* [http://www.wideopenwest.com/~jenkins/ironclads/ironclad.htm Ironclads and Blockade Runners of the American Civil War]
* [http://www.history.navy.mil/photos/sh-usn/usnsh-m/monitor.htm Images and text on the USS "Monitor"]
* [http://www.revistanaval.com/armada/buques_marinablindada/numancia.htm The Spanish Navy "Numancia", first ironclad warship to circumnavigate the world]
* [http://www.bruzelius.info/nautica/Ships/Naval_Science(1874)_p1.html Circular Iron-Clads in the Imperial Russian Navy]
* [http://www.hmswarrior.org/ HMSWarrior.org]