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 armour plates . The ironclad was developed as a result of the vulnerability of wooden warships to explosive or incendiary shells . The first ironclad battleship , , was launched by the French Navy in November 1859 . The British Admiralty had been considering armored warships since 1856 and prepared a draft design for an armored corvette in 1857 ; in early 1859 the Royal Navy started building two iron - hulled armored frigates , and by 1861 had made the decision to move to an all - armored battle fleet . After the first clashes of ironclads ( both with wooden ships and with one another ) took place in 1862 during the American Civil War , it became clear that the ironclad had replaced the unarmored ship of the line as the most powerful warship afloat . This type of ship would come to be very successful in the American Civil War . Ironclads were designed for several roles , including as high seas battleship s , coastal defense ships , and long - range cruiser s . The rapid evolution of warship design in the late 19th century transformed the ironclad from a wooden - hulled vessel that 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 ) , 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 cruiser s . Before the ironclad . The 15th century Korean turtle ship s are sometimes referred to as the first ironclads , though the extent of their iron armor is still debated , with some historians claiming that their metal protection was limited to anti - boarding spikes . The modern ironclad became technically feasible and tactically necessary because of developments in shipbuilding in the first half of the 19th century . According to naval historian J . Richard Hill : " The ( ironclad ) had three chief characteristics : a metal - skinned hull , steam propulsion and a main armament of guns capable of firing explosive shells . It is only when all three characteristics are present that a fighting ship can properly be called an ironclad . " Each of these developments was introduced separately in the decade before the first ironclads . Steam 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 propeller in the 1840s . 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 . The first purpose - built steam battleship was the 90 - gun in 1850 . " 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 " 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 - and 24 - pounder guns with 32 - pounders on sailing ships - of - the - line and introducing 68 - pounder s on steamers . Then , 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 , 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 . 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 . Iron armor . Following the demonstration of the power of explosive shells against wooden ships at the Battle of Sinop , and fearing that his own ships would be vulnerable to the Paixhans guns of Russian fortifications in the Crimean War , Emperor Napoleon III ordered the development of light - draft floating batteries , equipped with heavy guns and protected by heavy armor . Experiments made during the first half of 1854 proved highly satisfactory , and on 17 July 1854 , the French communicated to the British Government that a solution had been found to make gun - proof vessels and that plans would be communicated . After tests in September 1854 , the British Admiralty agreed to build five armoured floating batteries on the French plans , establishing the important Thames and Millwall Iron Works within the docks . The French floating batteries were deployed in 1855 as a supplement to the wooden steam battle fleet 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 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 . The British floating batteries and arrived too late to participate to the action at Kinburn . The British planned to use theirs in the Baltic Sea against the well - fortified naval base at Kronstadt . The batteries have a claim to the title of the first ironclad warships but they were capable of only 4 knots ( 7 km / h ) under their own power : they operated under their own power at the Battle of Kinburn , but had to be towed for long range transit . They were also arguably 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 , begun in 1857 and launched in 1859 . " 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 of 13 knots ( 24 km / h ) . She was armed with thirty - six rifled guns . France proceeded to construct 16 ironclad warships , including two more sister ships to " Gloire " , and the only two - decked broadside ironclads ever built , and . The Royal Navy had not been keen to sacrifice its advantage in steam ships of the line , but was determined that the first British ironclad 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 result was the construction of two s ; and . The ships had a successful design , though there were necessarily compromises between ' sea - keeping ' , strategic range and armour protection ; their weapons were more effective than that of " Gloire " , and with the largest set of steam engines yet fitted to a ship they could steam at 14 . 3 knots ( 26 . 5 km / h ) . Yet the " Gloire " and her sisters had full iron - armour protection along the waterline and the battery itself . " Warrior " and " Black Prince " ( but also the smaller " Defence " and " Resistance " ) were obliged to concentrate their armour in a central ' citadel ' or ' armoured box ' , leaving many main deck guns and the fore and aft sections of the vessel unprotected . The use of iron in the construction of " Warrior " also came with some drawbacks ; iron hulls required more regular and intensive repairs than wooden hulls , and iron was more susceptible to fouling by marine life . 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 . 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 " 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 . 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 . In May 1861 , the Confederate Congress voted that $ 2 million be appropriated for the purchase of ironclads from overseas , and in July and August 1861 the Confederacy started work on construction and converting wooden ships . On 12 October 1861 , the became the first ironclad to enter combat , when she fought Union warships on the Mississippi during the Battle of the Head of Passes . She had been converted from a commercial vessel in New Orleans for river and coastal fighting . In February 1862 , the larger ( " Merrimack " ) joined the Confederate Navy , having been rebuilt at Norfolk . As , " Virginia " originally was a conventional warship made of wood , but she was reconstructed with an iron - covered casemate when she entered the Confederate navy . By this time , the Union had completed seven ironclad gunboats of the , and was about to complete the , an innovative design proposed by the Swedish inventor John Ericsson . The Union was also building a large armored frigate , the , and the smaller . The first battle between ironclads happened on 9 March 1862 , as the armored " Monitor " was deployed to protect the Union ' s wooden fleet from the ironclad ram " Virginia " and other Confederate warships . In this engagement , the second day of 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 . 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 modeled on their namesake . The Confederacy built ships designed as smaller versions of the " Virginia " , many of which saw action , 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 , and she arrived in American waters just in time for the end of the war . Through the remainder of the war , ironclads saw action in the Union ' s attacks on Confederate ports . Seven Union monitors , including , as well as two other ironclads , the ironclad frigate " New Ironsides " and a light - draft , participated in the failed attack on Charleston ; one was sunk . Two small ironclads , and 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 , the Confederacy ' s most powerful ironclad and the gunboats , , . On the western front , the Union built a formidable force of river ironclads , beginning with several converted riverboats and then contracting engineer James Eads of St . Louis , Missouri to build the City - class ironclads . These excellent ships were built with twin engines and a central paddle wheel , all protected by an armored casement . They had a shallow draft , allowing them to journey up smaller tributaries , and were very well suited for river operations . Eads also produced monitors for use on the rivers , the first two of which differed from the ocean going monitors in that they contained a paddle wheel ( the and ) . Arguably Eads vessels were some of the better ironclads of the Western Flotilla , but there were a number of other vessels that served valiantly with the fleet . All were of varying design , some more successful than others , and some were similar to standard riverboats but with armored side - mounted paddle wheels . All were armed with various smoothbore and some rifled guns . If nothing else the experience of the American Civil War and its wild variety of competing ironclad designs , some more successful ( or disastrous ) than others , confirmed the emerging trade - off or compromises required in applying the latest technological advances in iron armour manufacture , ship construction and gun design — to name a few — also going on in Europe . There was no such thing as a ' perfect ' ironclad which could be invincible in every possible encounter ; ship duels , standing up to forts , Brown & Blue - water operations . The Union ironclads played an important role in the Mississippi and tributaries by providing tremendous fire upon Confederate forts , installations and vessels with relative impunity to enemy fire . They were not as heavily armored as the ocean going monitors of the Union , but they were adequate for their intended use . More Western Flotilla Union ironclads were sunk by torpedoes ( mines ) than by enemy fire , and the most damaging fire for the Union ironclads was from shore installations , not Confederate vessels . Lissa : First fleet battle . The first fleet battle , and the first ocean battle , involving ironclad warships was the Battle of Lissa in 1866 . Waged between the Austrian and Italian navies , the battle pitted combined fleets of wooden frigate s and corvette s and ironclad warships on both sides in the largest naval battle between the battles of Navarino and Tsushima . 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 — a double - turretted ram . Opposing them , the Austrian navy had seven ironclad frigates . 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 melée 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 . The superior Italian fleet lost its two ironclads , and , while the Austrian unarmoured screw two - decker 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 established it as the predominant naval power in the Adriatic . 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 . From the 1860s to the 1880s many naval designers believed that the development of the ironclad meant that the ram 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 SMS Erzherzog Ferdinand Max sinking the Italian " Re d ' Italia " at Lissa gave strength to the ramming craze . 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 that had actually been sunk by ramming struggled to be heard . 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 . 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 . 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 . 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 gun s also had the virtue of being lighter than an equivalent smoothbore and , because of their rifling , more accurate . 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 " 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 . 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 long ton ( 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 . From 1875 onwards , the balance between breech - and muzzle - loading changed . 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 , 16 - inch ( 406 mm ) guns of fired only once every 11 minutes while bombarding Alexandria during the Urabi Revolt . The 100 - ton , 450 mm ( 17 . 72 inch ) guns of could each fire a round every 15 minutes . 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 caused by a gun being double - loaded , a problem which could only happen with a muzzle - loading gun . 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 . carried two 16 . 25 - inch ( 413 mm ) breech - loading 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 . 1 - inch ( 460 mm ) armament of the Japanese of World War II . One consideration which became more acute was that even from the original Armstrong models , following the Crimean War , range and hitting power far exceeded simple accuracy , especially at sea where the slightest roll or pitch of the vessel as ' floating weapons - platform ' could negate the advantage of rifling . American ordnance experts accordingly preferred smoothbore monsters whose round shot could at least ' skip ' along the surface of the water . Actual effective combat ranges , they had learned during the Civil War , were comparable to those in the Age of Sail — though a vessel could now be smashed to pieces in only a few rounds . Smoke and the general chaos of battle only added to the problem . As a result , many naval engagements in the ' Age of the Ironclad ' were still fought at ranges within easy eyesight of their targets , and well below the maximum reach of their ships ' guns . 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 cannon s 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 . 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 of 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 and 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 . 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 . 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 . Furthermore , the adoption of ramming as an important tactic meant the need for ahead and all - round fire . These problems led to broadside designs being superseded by designs that gave greater all - round fire , which included central - battery , turret , and barbette designs . Turrets , batteries and barbettes . There were two main design 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 called a turret and when partially armored 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 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 . 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 . Ericsson was able to offer the heaviest possible turret ( guns and armour protection ) by deliberately designing a ship with very low freeboard . The weight thus saved from having a high broadside above the waterline was diverted to actual guns and armour . Low freeboard , however , also meant a smaller hull and therefore a smaller capacity for coal storage — and therefore range of the vessel . In many respects , the turreted , low - freeboard " Monitor " and the broadside sailer HMS " Warrior " represented two opposite extremes in what an ' Ironclad ' was all about . The most dramatic attempt to compromise these two extremes , or ' squaring this circle ' , was designed by Captain Cowper Phipps Coles : HMS " Captain " , a dangerously low freeboard turret ship which nevertheless carried a full rig of sail , and which subsequently capsized not long after her launch in 1870 . Her half - sister 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 of 1876 , which carried two turrets on either side of the centre - line , allowing both to fire fore , aft and broadside . 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 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 . Torpedoes . The ironclad age saw the development of explosive torpedo es as naval weapons , which helped complicate the design and tactics of ironclad fleets . The first torpedoes were static mines , used extensively 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 . 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 " Caio Duilio " and . 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 . 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 . 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 United States 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 . 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 " 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 . 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 . Iron and wood were to some extent interchangeable : the Japanese and ordered in 1875 were sister - ships , but one was built of iron and the other of composite construction . 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 , laid down in 1873 and launched in 1876 . " 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 . 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 . 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 of 1882 ) . 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 . The first ironclads to have all - steel armor were the Italian and . 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 . 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 , 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 , 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 . 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 . 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 . 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 " , 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 . Ships designed for coastal warfare , like the floating batteries of the Crimea , or and her sisters , dispensed with masts from the beginning . The British , 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 , built consistently mastless ironclads . 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 . 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 . , 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 . Sails persisted on ' cruising ironclads ' for much longer . During the 1860s , the French navy had produced the and es as small , long - range ironclads as overseas cruisers and the British had responded with ships like of 1870 . The Russian ship , laid down in 1870 and completed in 1875 , was a model of a fast , long - range ironclad which was likely to be able to outrun and outfight ships like " Swiftsure " . Even the later , 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 , , which was completed in 1888 . 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 , 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 ( decade ) . 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 struggled to maintain a deterrent parity with at least France , while providing suitable protection to Britain ' s commerce and colonial outposts worldwide . Ironclads remained , for the British Royal Navy , a matter of defending the British Isles first and projecting power abroad second . Those naval engagements of the latter half of the 19th - century which involved ironclads normally involved colonial actions or clashes between second - rate naval powers . But these encounters were often enough to convince British policy - makers of the increasing hazards of strictly naval foreign intervention , from Hampton Roads in the American Civil War to the hardening combined defences of naval arsenals such as Kronstadt and Cherbourg . There were many types of ironclads : 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 at times considered the risk - laden plan of engaging an enemy fleet in harbor as soon as war broke out . To this end , the Royal Navy developed a series of ' coast - defence 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 . As long - range monitors they could reach Bermuda unescorted , for example . However , they were still armed with only four heavy guns and were as vulnerable to mines and obstructions ( and enemy monitors ) as the original monitors of the Union Navy proved to be during the Civil War . The British prepared for an overwhelming mortar bombardment of Kronstadt by the close of the Crimean War , but never considered running the smoke - ridden , shallow - water gauntlet straight to St . Petersburg with ironclads . Likewise , monitors proved acutely unable to ' overwhelm ' enemy fortifications single - handed during the American conflict , though their low - profile and heavy armour protection made them ideal for running gauntlets . Mines and obstructions , however , negated these advantages ; a problem the British Admiralty frequently acknowledged but never countered throughout the period . The British never laid down enough " Devastation " - class ' battleships ' to instantly overwhelm Cherbourg , Kronstadt or even New York City with gunfire . Although throughout the 1860s and 1870s the Royal Navy was still in many respects superior to its potential rivals , by 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 . 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 . Few Egyptian guns were actually dismounted , on the other hand , and the fortifications themselves were typically left intact . Had the Egyptians actually utilised the heavy mortars that were at their disposal they might have quickly turned the tide , for the attacking British ironclads found it easy ( for accuracy ' s sake ) to simply anchor whilst firing ; perfect targets for high - angle fire upon their thinly - armoured topdecks . 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 weapon s 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 boat s 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 . 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 . Russia expanded her navy in the 1880s and 1890s with modern armored cruisers and battleships , but the ships were manned by inexperienced crews and politically appointed leadership , which enhanced their defeat in the Battle of Tsushima on 27 May 1905 . 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 . This started a new era of naval warfare . Ironclads were widely used in South America . Both sides used ironclads in the Chincha Islands War between Spain and the combined forces of Peru and Chile in the early 1860s . The powerful Spanish participated in the Battle of Callao but was unable to inflict significant damage to the Callao defences . Besides , Peru was able to deploy two locally built ironclads based on American Civil War designs , the " Loa " ( a wooden ship converted into a casemate ironclad ) and the ( an small monitor armed with a single 68 pdr gun ) , as well as two British - built ironclads ; , a centre - battery ship , and the turret ship . " 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 ' 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 and the at the Battle of Angamos Point . Ironclads were also used from the inception of the Imperial Japanese Navy . The ( 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 cruiser s . 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 . End of the ironclad . There is no clearly defined end to the ironclad , besides the transition from wood hulls to all metal . Ironclads continued to be used in World War I . Towards the end of the 19th century , the descriptions ' battleship ' and ' armored cruiser ' came to replace the term ' ironclad ' . 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 ' . Most of the ironclads of the 1870s and 1880s served into the 1900s ( decade ) . 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 . Legacy . The example of the ironclads had some bearing on the history of the tank , as ironclad warships became an inspiration for ideas of landships and other armored vehicles . H . G . Wells , in his short story " The Land Ironclads " , published in " The Strand Magazine " in December 1903 , described the use of large , armoured cross - country vehicles , armed with cannon and machine guns , and equipped with pedrail wheels Today . A number of ironclads have been preserved or reconstructed as museum ships .