The Wrong Ship at the Right Time: The Technology of USS Monitor and its Impact on Naval Warfare

Larrie D. Ferreiro
George Mason University

Introduction: “Forty patentable contrivances”

Among the many myths that grew up around USS Monitor was that she not only represented a revolutionary concept in naval warfare, marrying steam, armor and a revolving turret, but that her inventor, John Ericsson, had stuffed the ship chock-full of new technologies. This legend started with John S.C. Abbott’s The History of the Civil War in America, first published in the spring of 1863 even as the battles of Vicksburg and Chancellorsville were raging, and Gettysburg was still a lively manufacturing town untouched by war.  Abbott described Monitor as not “merely an iron-clad vessel, with a turret; but there are, in fact, between thirty and forty patentable inventions upon her, and the turret is by no means the most important one. Very properly, what these inventions are, is not proclaimed to the public”.  A generation later, Ericsson’s biographer, William Conant Church, writing just a year after his subject’s death, attributed the statement to Monitor’s first assistant engineer Isaac Newton, who “estimated…that she contained at least forty patentable contrivances.  Ericsson was urged by Mr. Newton to secure patents for these, but he declined to do so”.  These statements were quickly picked up by journals and magazines around the country celebrating the life of John Ericsson, and have been uncritically quoted ever since. 1

These widely-believed statements about the novelty of USS Monitor and the selflessness of her designer are patently false. John Ericsson was far too experienced an engineer to laden his project with untried and untested technologies.  He knew that he could not deliver such a novel ship as Monitor in one hundred days while simultaneously creating forty new devices that other men would have to learn how to build and install.  Instead, Ericsson reached back to tried-and-tested technologies that he and others had developed over the previous quarter-century.  An account written just a few days after the Monitor-Virginia duel had it right: “The Monitor is no new invention of Mr. Ericsson’s, but that she is the result of 25 years’ study toward an invulnerable siege battery.” 2    

This was shown by the technologies both used and not used aboard Monitor.  The screw propeller used on the ironclad, which Ericsson pioneered back in 1838, was now standard equipment on both commercial and military ships.  Monitor’s engine, his patented, double-trunk design that was more compact than the more widespread, single-trunk engine, was installed on the frigate USS Minnesota back in 1855 and had been operating for over six years without difficulty.  “These engines were of what has ever since been called the ‘Monitor type’, and many have supposed that they were, like the vessel itself, of wholly novel and untried design,” as Charles MacCord, one of Ericsson’s most trusted draftsmen, explained.  “This, however, was not the case… this form of engine had already demonstrated its practical working qualities, otherwise the captain would probably have given the first trials at the dock his personal supervision.”  Ericsson, himself, reassured Monitor’s supervisor of contracts, Commodore Joseph Smith, “Nothing is attempted not already well tried, or of so strictly a mechanical a nature as to be susceptible of previous determination.” In keeping with his philosophy of using only tried-and-tested technologies on Monitor, Ericsson did not make use of his own patented fresh-water distiller, still unproven in operational use. 3          

John Ericsson (NHHC Photo # NH 305)

The claim that “the inventions are… not proclaimed to the public” was decidedly wrong.  Neither John Ericsson nor Isaac Newton were self-effacing when it came to publicizing the militarily-sensitive technologies and tactics employed by the ship.  Even as Monitor was under construction in January 1862, Newton gave a talk, printed in the Journal of the Franklin Institute a few weeks later, which detailed the armor scheme of the turret, decks, and hull.   A few days after the Battle of Hampton Roads, at a meeting of the New York Chamber of Commerce, that was soon reported in papers nationwide, Ericsson explained that Monitor’s cannon shot did not penetrate the armor of Virginia because the guns were slightly elevated, but at the next encounter “they will leave the guns level, and they won’t mind if the ball strikes the water, because the ricochet will take it where they want it.  The next time they go out, I predict the third round will sink the Merrimac [Virginia].” 4     All this strategic intelligence undoubtedly found its way almost immediately to the Confederate Navy.          

Ericsson was clearly not the selfless inventor that Church portrayed.  In addition to using many of his already-existing patents on Monitor, he made certain that the most important ideas for his new ship would be protected under patent law.  The most novel feature of Monitor was its revolving gun turret, the first operational one in the world.  However, as the US Commissioner of Patents explained in 1863, Ericsson’s turret by itself was not a unique idea: “the improvements in this respect propose no change of general principle or mode of structure; they have reference to the perfecting of the details of construction, to additional or different supports, to facilities of rotation and to greater conveniences in working the guns.   Port-hole stoppers have received much attention, and, apparently, with valuable results”.   Indeed, a year after Monitor’s loss, Ericsson went on to take out patents on improved designs for his unique gun-carriage (designed to limit recoil in a confined space) and port-hole stopper (which protected the gunports from cannon fire when not in use) based on battle experience at Hampton Roads and elsewhere. 5      

Perhaps Ericsson’s greatest “contrivance” with the respect to Monitor was the invention of the need for a slow, shallow-draft, mobile coastal battery.  That requirement had not existed prior to Monitor’s construction and subsequent duel with Virginia.  The US Navy had, from the start, been a blue-water force, capable of bringing the fight to distant shores.  That had been as true for John Paul Jones’ Bonhomme Richard in 1779 as it was for the latest screw frigates and sloops launched just a few years before the outbreak of the Civil War; indeed, the only concession that the US Navy made to shallow-draft requirements was that the ocean-going 1859 Hartford class sloops drew ten feet less water than the Merrimack class frigates, in order to enter southern ports. 6   In fact, at the onset of the Civil War, the House Chairman of Naval Affairs, Charles Sedgwick, suggested that “Gun Sloops [were] a class of vessel more needed in the Navy than any other.” 7   The Union Navy had to carry out a close blockade along almost 3,500 miles of coastline, from Virginia to Texas. In addition, it had to contend with the potential threat of British and French vessels breaking neutrality.  These conditions all pointed to the requirement for ocean-going vessels. In fact, the Union Navy’s original request for bids for ironclad ships, dated April 7, 1861, called for vessels “to be rigged…to navigate at sea.” 8    

Ericsson’s Monitor changed all that.  She was the wrong ship at the right time, a brown-water ship designed for a blue-water navy.  By confronting CSS Virginia at Hampton Roads just in the nick of time to avert a naval catastrophe, she changed the course of maritime strategy for a generation by shifting the focus to littoral defense, not just in the United States but around the world.   

International technology transfer and the origins of USS Monitor in the Crimean War

Like many of the advanced weapons used during the Civil War, the technology of USS Monitor was largely transferred from abroad.  International technology transfer during the war generally took two distinct forms: direct purchase or knowledge transfer.  In the South, which was short on industrial capability, direct purchase was the more common avenue for quickly obtaining major weapons.  Confederate officers were sent abroad to purchase ships from Britain and France, such as the steam sloop CSS Alabama from Laird in Birkenhead and the ironclad ram CSS Stonewall from Arman in Bordeaux.    In the North, knowledge transfer was more widely used, as when the concept and general plans for USS New Ironsides were derived from the French ironclad Gloire.

One of the primary sources of overseas knowledge transfer came from the large immigrant community in the North, particularly around the major cities of Philadelphia and New York.   The United States was always a nation of immigrants, and those immigrants often brought their skills and ideas into service for the US military. Ericsson’s younger countryman, John W. Nystrom, had emigrated from Sweden to the United States in 1849, developing a novel screw propeller and various mathematical instruments.  During the Civil War, he served in Philadelphia as a naval engineer under Engineer-in-Chief, Benjamin Isherwood.

Ericsson, himself, had lived in Britain for many years and brought with him the concepts he had developed there while exposed to other similar inventions, including the screw propeller, revolving turret and forced draft-blowers. 9 He had conceived of Monitor long before the Civil War, not as a solution to the American needs for blockade and preventing overseas interference, but rather as the answer to a problem from a foreign conflict fought just a few years earlier: the Crimean War.

The Crimean War (1853-1856), between Russia and an alliance of Britain, France, and Turkey, was in many ways the first industrial war that presaged many of the technologies and tactics used during the American Civil War, including: telegraph and railroads; field hospitals; photography; trench warfare; steamships; and armored vessels.   In 1855, Secretary of War (later Confederate President), Jefferson Davis, sent observers to the Crimean War under the Delafield Commission, which included then-Captain George McClellan (later General-in-Chief of the Union Army), who returned with a deeper understanding and acceptance of how to use these new technologies on the battlefield and behind the lines.

The armies of both North and South adopted several weapons that were developed for, or saw service in, the Crimean War.  The Minié ball, originally invented by a French army officer, provided more reliable and had longer-range hitting power than previous bullets, and was used widely by French and British troops during the Crimean War.   It was brought to the United States in 1855, and within a few years an improved version became standard issue for all American soldiers just prior to, and during, the Civil War.  The 1853 British Enfield rifle-musket, which fired the Minié ball, also became standard American issue.  The French canon obusier de 12 cm, developed in 1853 and which could fire a wide range of ammunition, was adopted as the “12-pounder Napoleon” by both North and South.     

The Crimean War also provided the impetus for American naval developments in the Civil War.  In 1855, the Russian Navy approached the French inventor Brutus Villeroi to build a submarine that could destroy French and British warships. Villeroi had previously developed submarines for salvage work, but it is doubtful that he answered Russia’s call, as the following year he emigrated to Philadelphia where he continued his work on submarines.  In 1861, as the crisis with CSS Virginia loomed, he proposed his newly-built submarine Alligator to the Union Navy “to blow up one or more vessels of war at the Norfolk Navy Yard for a sum equivalent to the damage inflicted upon the enemy, to be paid… on the destruction of the property.”  Although the bids for three ironclad warships were already being prepared to accomplish exactly the same task, the Union Navy accepted his proposal as an alternate plan.  As it happened, Villeroi delivered his submarine two months after the Battle of Hampton Roads, so the Union Navy found other uses for the vessel. 10          

The Crimean War was most notably the birthplace of the shallow-draft armored steam battery, which was the direct ancestor of Monitor. By 1854, both France and Britain had recognized that existing wooden warships were inadequate to attack heavily-defended Russian forts, as warships were too deep to closely approach the fortifications, and vulnerable to shore batteries.  The French Emperor Napoleon III, himself a student of artillery, prodded his naval constructors to develop a fleet of steam-powered, heavily-armored, shallow-draft ships that could closely approach Russian forts in the Baltic and the Black Sea.  Napoleon III wanted ten ships available for the 1855 campaign, but the French shipyards could build only five in that short a time. Undeterred, the French Navy contacted their British allies and provided drawings and specifications for British shipyards to build another five. In the event, only three French batteries were completed in time for the 1855 attack on the fortress at Kinburn on the Black Sea.

Bombardment of Kinburn (Weapons and Warfare)

Fort Kinburn guarded the entrance to the Bug and Dnieper rivers, and the access to the critical shipbuilding port of Nikolayev. In the summer of 1855, the three available French batteries were towed into position before the fort.  Enclosed by 4 inches of wrought iron plate, each battery could maneuver slowly at about 4 knots to deploy sixteen heavy broadside guns at their target.  During the battle on October 17, 1855, the three batteries fought at a range of about 800-1,000 yards, and unleashed over 3,000 shell and shot which, combined with the shelling from rest of the fleet, caused the Russians to surrender in less than eight hours.  In return, the ironclad batteries were struck repeatedly with little damage except for dents and furrows in the armor.  The French Navy attributed the prompt victory “to the fire of the floating batteries which… opened breaches in the ramparts and with remarkable precision was able to knock down the solidest walls.” 11          

At the same time the siege of Kinburn was being planned in 1855, a young naval lieutenant named Cowper Phipps Coles built an armed raft that bombarded a Russian town near the city of Rostov-on-Don.  Flush with success and aware of the recent action at Kinburn, Coles drew up plans for an armored raft fitted with a hemispherical cupola that could be used to attack other Russian forts. The great British civil engineer, Isambard Kingdom Brunel, suggested to Coles some improvements regarding a revolving turntable, so that one would “turn the gun, not the ship.”  In 1859 and 1860, Coles drew up patents for a revolving, armored, cone-shaped cupola. In the autumn of 1861, just as Ericsson was designing Monitor, the British Navy built and tested a model of Cole’s cupola on the steam battery HMS Trusty.  Trusty successfully fired her 40-pound gun and received close-range shots from cannon ranging up to 100 pounds with few ill effects. 12 (April 5, 1862), p. 5; Stanley Sandler, The Emergence of the Modern Capital Ship (Newark, Delaware: University of Delaware Press, 1979), p. 179.  For the cupola trials on HMS Trusty, see Coles’ testimony in Report from the Select Committee on Ordnance (London: House of Commons, 1863), pp. 66-67.]

While the Crimean War was raging, Ericsson was making a comfortable living as an engineer in New York City, while also developing his caloric engine and testing it aboard his paddlewheel ship Ericsson.  Ever since the disastrous affair with USS Princeton in 1844 (where he was wrongly blamed for a gun explosion that killed the Secretaries of State and Navy) he had largely given up military work. 13   However, apparently intrigued by the nature of the Crimean War as the first industrial conflict, on September 26, 1854, he dashed off a proposal to Napoleon III that described “a new system of naval attack”: a short-range, steam-powered, iron-hulled vessel with curved decks and a hemispherical armored turret [that] would not show any right angle to an incoming shell, thus deflecting it away from the guns and machinery.  The turret would turn on a single, central spindle.  The hull was designed with a long overhang to protect the rudder and propeller.  The engines and internal compartments would be supplied with air by forced-draft blowers. 14   Although the French Navy never made use of this concept, it would turn out that Ericsson’s 1854 Crimean War proposal would become the template from which Monitor would be created.    

The Union Navy Department issues requirements for ocean-going ironclads, but John Ericsson and the Ironclad Board ignore them 

News that a Confederate ironclad was rising from the burned-out hulk of USS Merrimack was the spur for the construction of Monitor. Merrimack had been burned and sunk in April 1861 when Union troops abandoned the Gosport naval base.   By May, the Confederate Navy had raised the hulk and placed it in drydock, and in June, design work began on the conversion to the armored CSS Virginia.  The Union Navy received word of the new ironclad even before the work had actually commenced, and on July 4, Secretary of Navy, Gideon Welles, requested Congress to authorize construction of ironclad steamers.  Welles subsequently enlisted the help of Connecticut businessman Cornelius Bushnell to get a bill onto the floor and round up the votes. 15    

The Union already had one ironclad steamer on the ways, but it had lain unfinished in Hoboken, New Jersey since 1856 and could not be completed in any reasonable time.  The Stevens Battery had been ordered by the Navy in 1841 at the urging of two prominent railroad engineers, Edwin and Robert Stevens, who conceived of a fast, heavily armed and armored, semisubmersible, ocean-going steamer that could reinforce the Port of New York.  Over the course of fifteen years, the ship grew in size and complexity but without ever being launched, even as the brothers continued to receive navy funding.  By 1861, it was a 420-foot-long hull resting on open ground, having no decks, armor or guns fitted, with boilers and machinery in place but no propellers.  Naval experts who examined the ship in her unfinished state determined that she would be of “doubtful success,” and recommended against the “expenditure of important sums of money” to complete the work. 16

USS Monitor Plans (Wikimedia Commons)

On August 3, Congress authorized $1.5 million (the equivalent of $6 billion in 2018) to order “iron or steel-clad steamships or floating steam batteries” and an Ironclad Board to examine industry proposals. 17   Although the currently-building CSS Virginia had been the catalyst for the construction of ironclads, it was not, in the view of the Union Navy, their primary adversary. The Civil War was, to that point, primarily a conflict between two land powers, North and South, and therefore mainly under the Army’s purview.  The Union Navy, by contrast, had to plan against a spillover of the American conflict into a wider war with Britain and France, which had already demonstrated their preference for the Confederacy.  The Union Navy could only do this by exhibiting American naval strength on the high seas: “A foreign war must be waged almost exclusively upon the ocean…in view of the settled hostility of England and France, we ought to prepare ourselves to cope with their navies, through which alone they can strike us.” 18 With the French ironclad Gloire and the British ironclad Warrior already in the water, the Union Navy had to continue its time-honored blue-water posture in order to meet current and future threats.     

For this reason, the Union Navy Department issued the request for bids on August 7, 1861 – less than a week after Congress established the Ironclad Board — ignored Congress’ allowance for coastal “floating steam batteries” and specifically called for ocean-going ships: 19                


The Navy Department will receive offers from parties who are able to execute work of this kind, and who are engaged in it, of which they will furnish evidence with their offer, for the construction of one or more iron-clad steam vessels of war, either of iron or of wood and iron combined, for sea or river service, to be of not less than ten nor over sixteen feet draught of water; to carry an armament of from eighty to one hundred and twenty tons weight, with provisions and stores for from one hundred and sixty-five to three hundred persons, according to armament, for sixty days, with coal for eight days. The smaller draught of water, compatible with other requisites, will be preferred. The vessel to be rigged with two masts, with wire-rope standing rigging, to navigate at sea.    

The advertisement appeared in the New York Times, Boston Daily Journal, Philadelphia Evening Journal and many others across the Northeast, as well as being spread by word of mouth. 20   By the third week of September, the Navy Board had 16 proposals in hand, from which they selected three widely different concepts for construction that the Union Navy would then evaluate for further use. 21   In effect, the Union Navy was relying on the shipbuilding industry to perform, on its behalf, the experimentation (today we would call it research and development) for this new breed of vessel. This was, in fact, the normal course of action during the mid-nineteenth century.  At that time, the only navy-led experimentation was focused on gunnery, at John Dahlgren’s “Experimental Battery” in the Ordnance Establishment at the Washington Navy Yard. 22  

For hull and machinery developments, the US Navy, as with most European navies, looked to civilian manufacturers to take the lead. In the mid-1800s, commercial firms were quickly developing new types of engines and propellers, as well as improvements in iron shipbuilding, for a rapidly expanding transatlantic and global trade.  It was quite common for the US Navy to buy two or more competing technologies and compare them side-by-side.  For example, when Congress authorized the Navy to build six steam frigates in 1854, a special board was convened that decided the ships should be outfitted with different types of engines manufactured by several builders, in order to evaluate the varying engine types and to encourage competition. Four of the ships were fitted with single-trunk engines, one with a steeple engine and one, USS Minnesota, was built with Ericsson’s double-trunk engine. 23              

This pattern held true for the Union’s ironclad program. The first concept selected had been submitted by the Philadelphia firms of Merrick & Sons (engine manufactures) and William Cramp & Sons (shipbuilders) for a 4,000-ton, ocean-going, casemate (i.e., broadside battery) ironclad. The ship, later named New Ironsides, was roughly based on the new French ironclad frigate Gloire, though considerably smaller, slower and with fewer guns, but still the largest warship the United States had built to date. Her wooden hull, carrying 14 Dahlgren smoothbore guns and four others, would be protected by hammered iron plate 4.5 inches thick.  This type of ship, more than any of the other ironclad concepts selected, was closest to the concept of an ocean-going warship that could provide some deterrence against the ironclads now on the building ways in Britain and France. 24      

The second concept, later named Galena, was proposed by Cornelius Bushnell and his consortium of shipbuilders and designed by Samuel Hartt Pook. Much closer to the “gun sloops …more needed in the Navy than any other” advocated by Sedgwick, Galena was a small (950 tons), slow, narrow casemate ironclad with six guns and just 3 inches of side iron plating. The Ironclad Board worried that the ship “would not float her armor and load sufficiently high, and have sufficient stability for a sea vessel” so required a “guarantee that it could do these.” Bushnell, on the advice of his colleague, Cornelius Delamater, owner of the Delamater Iron Works in New York City, called on John Ericsson in order to help him provide this “guarantee.”  Ericsson, in addition to verifying Galena’s stability, showed Bushnell a copy of his own long-dormant “new system of naval attack” that he had sent to Napoleon III.  Bushnell, convinced of the utility of this novel ship, took Ericsson’s plans to Gideon Welles, and within a few days, the Ironclad Board approved this third concept for construction. Ericsson, who claimed he could finish the vessel in ninety days, began work on his vessel, which he later named Monitor, even before the contracts were signed. 25

Whereas the proposals for New Ironsides and Galena more or less hewed to the Navy’s request for ocean-going ships of long endurance, the third concept — Ericsson’s Monitor — met none of the Navy’s stipulated demands for weight of armament, number of crew, or seaworthiness.  He had simply ignored them in favor of presenting the small, shallow-draft battery that he had formulated seven years earlier for the Crimean War.  He later justified this total disregard for the Navy’s requirements by citing the more pressing need to stop CSS Virginia: 26        

  • The work on the Merrimac [sic, i.e., Virginia] had progressed so far that no structure of large dimensions could possibly be completed in time to meet her.
  • The well-matured plan of erecting a citadel of considerable dimensions on the ample deck of the razed Merrimac admitted of a battery of heavy ordnance so formidable that no vessel of the ordinary type, of small dimensions, could withstand its fire.
  • The shallow waters on the coast of the Southern States called for very light draught; hence the upper circumference of the propeller of the battery would be exposed to the enemy’s fire unless thoroughly protected against shot of heavy caliber. A difficulty was thus presented, which apparently could not be met by any device that would not seriously impair the efficiency of the propeller.

Ericsson’s argument for shallow draft was questionable; he certainly would have known that Virginia drew over 20 feet of water, so Monitor could have been just as deep and still operated successfully. On the other hand, his justification for building a small ship “in time to meet” the Confederate ironclad was completely correct. Even as the proposals were being read in September 1861, Virginia was already being refurbished in the Gosport dockyard, while the Tredegar Iron Works in Richmond was busy rolling out its iron cladding.       

For its part, the Ironclad Board was complicit in overlooking the original requirements for an oceangoing vessel, albeit with some reservations: “we are somewhat apprehensive that her properties at sea are not such as a seagoing vessel should possess,” and could only be moved along the coast in smooth water. Nevertheless, given the urgent need to have a ship ready in just four months, the members recommended funding Ericsson’s “experiment,” as they dubbed it, and Welles agreed. 27   Nevertheless, the contract with Ericsson, signed on October 4, contained a clause calling for “masts, spars, sails and rigging” that could propel the vessel at six knots in a “fair breeze of wind.” 28   Thus, the Navy continued to maintain (as its August request for bids stipulated) that it still wanted an ocean-going vessel instead of a mobile, coastal battery designed for the littorals. Ericsson simply ignored this part of the contract, and it appears that he was never pressed on this matter. And for good reason; the Union Navy was now in a race to complete its ironclad before the Confederate Navy, already with a 3-month head start, could complete its own.   

Design, build and control mechanisms for USS Monitor

Ericsson claimed that he could build the vessel in 90 days, but the Navy gave him 100 days, and his contract held him to that schedule. In order to accomplish this, Ericsson had to ensure three things: his design had to be easily producible; he had to have reliable sources of manufacture for all armor, engines and equipment; and he required strong control mechanisms to be certain that each piece of equipment fit into place and worked as intended, without prototypes or testing.       

Ericsson quickly modified his 1854 proposal to make the ironclad easier to build. The hemispherical turret, with curves in three dimensions that would have had to be hand-crafted, was jettisoned in favor of a cylindrical turret whose armor could be machine-rolled in two dimensions from flat plates. Likewise, a flat the deck replaced the curved one. The hull itself divided in two sections, and unlike Ericsson’s 1854 all-iron concept, was a composite iron and wood structure.  The lower hull was essentially a 124-foot-long, 6-foot-deep iron bathtub divided in half by a main transverse bulkhead. Engines and machinery were aft of the bulkhead, accommodations forward, and the turret sat atop it. The flat upper “raft” was of standard warship oak-beam-and-pine-deck construction, to which iron plate was bolted on the deck and sides.  The upper raft fitted snugly over the lower bathtub, strengthened with heavy brackets and riveted together. 29   Ericsson chose standard thicknesses for the iron plating, typically 3/8-inch and 1/2-inch thick. Armor plates were limited to 1-inch thickness to ensure that existing mills and factories could quickly produce and bend them with no time-consuming modifications to the plants. As described earlier, all the machine technology was well-proven and known to manufacturers.    

The second necessity to meet the 100-day construction period was reliable manufacturers.  The signers on the Navy’s contract to build Monitor were Ericsson, Bushnell and two other individuals – John F. Winslow, co-owner of the Albany Iron Works, and John A. Griswold, owner of the Rensselaer Iron Works in Troy. These four men formed the core of a close-knit network of ironworks, foundries and machinery builders, based almost exclusively in New York State, which together would create the various parts that became Monitor. The mutual levels of trust that had already existed between these manufacturers allowed them to quickly dole out work and plan deliveries accordingly, without resorting to time-consuming contractual negotiations, and also ensured that the quality of work would be at the highest levels.    

The group contracted with the Continental Iron Works in Green Point, Brooklyn to actually assemble the vessel. Most of the individual parts were subcontracted out. It was already understood that the Delamater Iron Works, which had built many engines for Ericsson, would supply the main engines, boiler and propeller, while Albany Iron Works and Rensselaer Iron Works would supply the plate iron, angles, columns and brackets. Smaller companies in New York City and Green Point would supply additional material or furnish and install fittings and equipment, such as E.W Barstow for the anchor chain, H.R. Worthington for the bilge pumps, and the broker Holdane and Company for timber and angle iron. 30

Monitor Turret (Wikimedia Commons)

The turret, by far the most unique and complicated assembly on the ship, was further subcontracted.  The only Northern mill that was both within reasonable transport distance of New York City, and which could roll large sheets of 1-inch plate, was H. Abbott & Sons of Baltimore, Maryland.  These sheets were transported to Novelty Iron Works in New York City, which rolled the plates into semicircles and assembled them to form the turret. The steam engines that turned the turret, as well as the gun carriages inside, were manufactured by the Clute Brothers Foundry in Schenectady.  The iron “port stoppers,” which were 8-inch-thick slabs of hammered iron that swung like pendulums to protect the guns when not in use, were forged at the Niagara Steam Forge in Buffalo. 31   The Dahlgren guns themselves, which had been manufactured in 1859 at the West Point Foundry at Cold Spring, New York, were transferred from the sloop USS Dacotah.

By keeping almost all of the subcontracted iron work within New York State, the builders were making use of reliable transport by rail, barge, and canal to ensure rapid delivery of finished parts.  Another reason for “buying local” was that Monitor was not the only ironclad under construction at that time, and iron supplies were still relatively scarce. Indeed, the Albany Iron Works and Rensselaer Iron Works were already furnishing iron parts for both Monitor and the armor system for USS Galena, then on the ways in Mystic, Connecticut.  The William Cramp & Sons shipyard in Philadelphia was already building USS New Ironsides, whose armor (4.5 inches thick) was produced using the Pennsylvania network of forges in Pittsburgh and Bristol. 32   Meanwhile, forges in the West were supplying iron for the Union Army’s seven City class armored gunboats under construction in James B. Eads’ shipyards in St. Louis, Missouri (they were also known as “Pook’s Turtles” after their designer Samuel Moore Pook, the father of Galena’s designer).  This sudden rush of ironclad construction, coupled with the increased demand for such wartime materiel as railroad rolling stock and fixed stock, put a strain on the iron supply network.

The third necessity to deliver the ship in 100 days was a strong set of control mechanisms over the actual construction of the ship. Ericsson had the central role in this, for, by all accounts, the entire design – right down to the individual plates, girders, pumps and pipes – came from the drawing room he had specially built in the Continental Iron Works, where he could also oversee the assembly and construction.  His output was prodigious – he produced somewhere between 150 and 300 drawings over the space of 152 days, or between one and two complete drawings per day.  In addition to these drawings, Ericsson was also continuously calculating and recalculating bills of material, weight of equipment, transverse stability, etc. as the design evolved. 33    

The extensive subcontracting of individual equipment, and the short timeframe for construction, meant that the usual methods for ensuring proper fit between components — which usually meant creating full-sized templates from existing equipment and extensive rework – could not be used.  A pump manufacturer in Schenectady would never see the mounting bracket or pipe their pump was connected to, so each factory had to build each part exactly according to the drawings, and the drawings themselves could allow no room for error. Ericsson, having been an artillery officer and surveyor in Sweden and an engineer in Britain, was a consummate draftsman in his own right and expressed himself eloquently through his drawings. Machinists who built the engines of USS Princeton to his drawings recalled they were “marvels of neatness and accuracy to scale.” 34

Ericsson’s biographers (and indeed, Ericsson himself) often portrayed the building of Monitor as a one-man show, with himself overseeing every aspect of design and construction.  In fact, his original drawings had to be painstakingly reproduced with complete accuracy in order to be sent to the various subcontractors. Ericsson employed a number of draftsmen like Charles MacCord, whose job was to take the original drawings, usually ink on heavy drawing paper, and copy them in pencil to a linen tracing cloth that could be easily transported to other factories. Navy men on-site performed oversight of the contract and construction.  Navy oversight of the ironclads was not administered, as was normally the case for shipbuilding, through the Bureau of Construction, Equipment and Repair – they had their hands full building and maintaining conventional wooden warships.  Instead, for Monitor, oversight was split between Commodore Joseph Smith of the Bureau of Yards and Docks for contracts, and Alban Stimers of the Engineer Corps (which was nominally in charge of all steam machinery) for construction. 35    

Thus, despite every appearance of being a rush job, the construction of USS Monitor was actually a carefully orchestrated affair that came about through long years of preparation. Ericsson had already thought about and planned the ship for seven years, so when the call came, it was more akin to filling in the details than starting afresh.  He made use of tried-and-tested engines, machinery and equipment, and simplified his design so the vessel could be quickly built of iron and wood using existing manufacturing processes. His long collaboration with a tightly-knit network of factories and foundries meant they could plan and deliver the required machinery and equipment in a steady stream. His own skill as a draftsman, and the skills of his subordinate draftsmen and Navy overseers, meant that each step of the design and build process went relatively smoothly. The one area of uncertainty, the performance of Monitor’s unique armor, was addressed in the contract by stipulating that the Navy would not have to accept the ship until “the impregnable battery” was tested “under the enemy’s fire”; Ericsson himself agreed that “if the structure cannot stand this test, then it is useless.” 36 Although the ship would be finished almost two months later than the promised 100 days, it turned out to be a “just-in-time” delivery.      

USS Monitor as an integrated weapon system avant la lettre

John Ericsson’s careful planning of Monitor’s construction was part and parcel of his ability to clearly envision the ship as a complete system.  He consciously used that word to describe his ship and its associated equipment, in an era when “system” more commonly described a philosophy of utility (“system of education”) than a collection of machinery. 37 Ericsson conceived of his turret ship as a “sub-aquatic system of naval warfare… an impregnable and partially submerged instrument for destroying ships of war.” 38   Every part of the ship’s design was bent to bringing its primary weapons, the guns, to close range with an enemy. The revolving turret allowed the ship to engage the enemy at almost any angle, not just broadsides, so it could fight even in confined waters. The small, heavily-armored turret would be just about the only thing enemy vessels could reliably fire upon except at close range, for the extremely low freeboard – Ericsson understood that the deck would frequently be awash – meant that the hull itself presented almost no target to long-range shells.  The “sub-aquatic” nature of the design demanded novel layouts and features for the machinery and crew, including forced ventilation for the engines and accommodations, a protected propeller, an anchor that could be raised and lowered from within the ship, and even toilets that could drain while underwater. USS Monitor was, in today’s terms, a fully integrated weapon system.   

The guns, however, which were the keystones in this integrated weapon system, were the only parts over which Ericsson had no control.  American naval guns on the eve of the Civil War were, in fact, state-of-the-art worldwide.  Although breech-loaders and rifled guns were in use at the time, navies still relied on smoothbore muzzle-loaders for larger caliber guns like those installed on Monitor. Developments by US Navy and Army artillery officers, notably John Dahlgren, Robert Parrott, and Thomas Rodman, had greatly increased both the safety and hitting power of American guns over their predecessors, so that they were comparable in performance to Britain’s Armstrong and France’s Paixhans guns. 39      

Ericsson had originally designed Monitor to carry two 12-inch guns, and his initial drawings showed the guns firing in opposite directions within the turret.  However, no 12-inch naval guns existed at the time in the United States.  The only comparable weapon was the Union Army’s single experimental 12-inch Rodman rifle gun, which at the time, was sitting idly at Fort Monroe in Virginia, at the entrance to Hampton Roads. Therefore, Ericsson was forced to employ the largest naval gun then in use, the XI-inch (11-inch) Dahlgren gun, a pair of which would be mounted side-by-side in the turret. Alban Stimers proposed a shortened version to more easily fit within the turret’s confined space, but there was no time to cast such a specialized weapon. Instead, Ericsson had to rely upon the 44-year-old Lieutenant John L. Worden, recently placed in command of Monitor, to secure its XI-inch guns.  The only ones available in New York were aboard the steam sloop USS Dacotah, which had just arrived from the East Indian Squadron patrolling off China.  Worden requested the Brooklyn Navy Yard to remove Dacotah’s guns and have them brought to the Continental Iron Works for installation aboard Monitor. 40    

Ericsson, meanwhile, had designed a pair of gun carriages that employed a unique braking system to check the recoil of the guns within the tight confines of the turret, although the basic concept was not very different from carriages then used aboard British warships.  The braking system used a friction gear (also called a compressor) tightened by a rotary hand-wheel. The guns themselves were run in and out using a block-and-tackle system. The braking system was sometimes ineffective or incorrectly used, for as archeological evidence would later show, the rear wall of Monitor’s recovered turret was dented by repeated strikes of the guns’ cascabels (the protruding knobs at the rear of the gun, used to tie off the tackle).  Although a similar carriage design was employed on the subsequent Passaic class monitors, Ericsson himself was apparently dissatisfied with this arrangement, for the following year he patented a newer, much different gun carriage that used a lever instead of a hand-wheel to tighten the friction gear, and employed a rack-and-pinion system instead of block and tackle to run the guns in and out. 41

In January and February 1862, with the ship now afloat, the guns and carriages were placed inside the most novel feature of the ship – the rotating armored turret.  The name of its builder, Novelty Iron Works, only underscored how unique it was. Just over 21 feet in diameter, it was built up of eight layers of 1-inch plate that had been carefully rolled at Novelty and assembled for fit.  Weighing almost 120 tons, it was too heavy to lift by crane, so it was disassembled for shipment across the East River to Continental Iron Works.  Once aboard ship, the turret was reassembled around the guns and carriages (the armor was bolted through) and the gunports carefully cut out. The two teardrop-shaped port stoppers were hinged at the top of the turret, normally covering the gunports, but would be swung inboard, out of the way when the guns were fired.  As it happened, the stoppers interfered with one another when swung open, so only one stopper could be opened at a time, halving the ship’s effective firepower. The outside structure of the turret normally rested on a brass ring embedded in the deck, which was intended to create a watertight seal when the turret was not in use. The turret was turned by a single 12-inch diameter central spindle connected at the base of the turret, which was rotated via gears by two small single-piston steam engines. To allow free rotation during battle, the entire turret was lifted off the deck by hand-screwing a wedge-shaped key under the spindle. 42          

Though Ericsson’s concept of mounting the guns inside a rotating structure dated to the Crimean War, other inventors had come up with similar ideas at about the same time.  Cowper Coles in Britain, as mentioned, had designed, patented, and tested a rotating cupola even while Monitor was under construction. Coles’ turret differed from Ericsson’s primarily in that, while Ericsson’s turret was supported on a central spindle, Cole’s was supported on roller bearings under the turret’s circumference.  (As it would turn out, all later turret designs, including those built by James B. Eads, would use Coles’ approach, which was more efficient and gave greater stability to the turret.)  Although Coles claimed paternity over the rotating turret, it presented no threat to Ericsson’s invention as Coles was in Britain.  In the United States, however, an inventor named Timothy Timby had submitted a patent caveat (similar to a provisional application, but short of a full patent) for a land-based rotating battery.  Although Timby’s two-story 100-foot diameter tower bore no resemblance to a sea-going turret, Ericsson’s partners –against Ericsson’s own wishes — decided pre-emptively to award Timby a royalty on Monitor’s turret to prevent further claims. 43

Compared with artillery developments, which were quite on par with those of Europe, American armor lagged significantly behind that of France and Britain. The Crimean War had convinced both nations of the utility of armored ships, but that first-hand experience was of course lacking in the United States.  Both France and Britain conducted extensive testing of armor against shell and shot, generally agreeing that about 4.5 inches solid plate was sufficient against the heaviest shells. Of perhaps equal importance was the finding that armor effectiveness varied as the square of the thickness.  Therefore, by the logic of the day, simply laminating two sheets of 2.25-inch plate would be half as effective as a single 4.5-inch plate (2.252 + 2.252 = 10, 4.52 = 20), while even five laminated 1-inch plates would be only a quarter as effective. 44            

Although Ericsson was well aware of these findings, it would have been impossible to build a ship in 100 days with such thick plates. As mentioned, H. Abbott & Sons of Baltimore, Maryland was the only East Coast factory that could roll even 1-inch plates; when queried about turning out 4-inch-thick plates, Abbott had replied that it would have required two additional months to alter the machinery, an unacceptable delay.  The other two factories that could turn out such plates, Bailey, Brown and Company of Pittsburgh and Bristol Forge of Bristol, Pennsylvania, were already fully engaged in producing armor for USS New Ironsides.  Ericsson used the 1-inch plate to build the turret and to cover the deck and sides for protection.  Reminded at regular intervals by Commodore Smith that the vessel “was much needed now,” Ericsson fretted about the freeboard and was continuously adjusting the thickness of the armor to ensure the ship floated properly at its design waterline. 45   He maintained the turret thickness at the original 8 inches, but reduced the deck armor from 2 inches to an inch, and side armor from 6 inches to 5, tapering to 3 inches below the waterline. 46

The ship’s boilers and propulsion machinery had to be adapted to their “sub-aquatic” existence, and suffered accordingly. The two double-furnace, horizontal-tube Martin boilers (named for their inventor Daniel B. Martin) were entirely below the waterline, so had to draw air through the engine room via a pair of steam-powered, centrifugal forced-draft blowers, known at the time as “air pumps.”  Forced-draft ventilation was already in wide use — Ericsson had employed it on USS Princeton almost twenty years earlier — but Monitor’s arrangements made its use particularly troublesome. Since the blowers were steam-driven, they could not operate until steam was raised, and this was a very slow process on Monitor because there was little natural air circulation through the boilers. Boilers in conventional steamships developed this circulation by drawing in air low, near the level of the boilers, and exhausting it through a high smokestack or funnel (called a “chimney” at that time). On Monitor, both the intakes and exhaust were at the same deck level, so there was little natural draw.  Worse, both the intakes and exhausts were simple grates through the deck, which were protected from flooding by short iron boxes.  These boxes were removed before battle, making the system certain to flood in all but the calmest water.  (In November 1862, when the ship was brought to the Washington Navy Yard for overhaul, it was fitted with a telescoping funnel that successfully addressed this problem.). 47

There were also problems with Ericsson’s patented horizontal double-trunk engine, also called a “vibrating lever” engine, as the piston rods oscillated in a semicircular motion instead of a fully circular rotation. He chose this design in order to fit within the protected below-deck space required for “sub-aquatic” warfare.  It was more compact than conventional engines and reasonably reliable, but as Engineer-in-Chief, Benjamin Isherwood, later determined, quite inefficient. The primary difficulty was excessive steam condensation inside the cylinders; with the two cylinders having an adjoining wall, they experienced large temperature changes, which caused steam to prematurely condense and rob the engines of power. Isherwood determined that Ericsson’s engine was about 12 percent less efficient than engines more commonly in use, which meant lower delivered horsepower and higher fuel consumption. 48

Monitor had a very standard machinery system, with several steam pumps and motors driven from the main boilers:  two blower motors, two turret motors, a bilge pump and a feed pump. Most navy and commercial ships, by 1861, had steam-driven bilge pumps, blowers and feed pumps. HMS Warrior, for example, had a single steam-driven blower, two boiler feed pumps, ash hoists and bilge pumps, while Cunard and Collins line passenger ships were fitted with various bilge pumps, blowers and feed pumps. 49 All other machinery was hand-driven.  The semi-balanced rudder, for example, was moved by a standard wheel-and-rope system from inside the pilot house forward. The four-fluked anchor, located in a well just aft of the bow, was raised and lowered from inside the ship by a hand-driven capstan.

Monitor’s propeller was a fairly standard 9 foot diameter, four-bladed model, quite different from the six-bladed propeller Ericsson installed on Princeton.  Given that the ship had a 10 foot draft and that Ericsson did not want the propeller protruding below the keel, the hull around the propeller had to be shaped to form a sort of upside-down well. This created serious impediments to the flow into the propeller, which undoubtedly contributed to later problems with speed (the ship could make only 6-7 knots, instead of the promised 9 knots) and maneuverability. Immediately above the propeller, the hull and deck opened to a removable iron grate which could be used to access the propeller for repair.         

Forward of the machinery were the accommodation spaces and the heavily-armored pilot house, which extended above the deck.  As mentioned previously, a single transverse bulkhead divided the ship into machinery spaces aft and accommodations forward.  Unlike previous naval and merchant ships which berthed crew forward and officers aft, on Monitor all officers and crew (generally between 58 and 63 men total) had to be squeezed into the forward section of the ship.  The accommodation spaces, entirely below the waterline, were supplied with air through the starboard, forced-draft ventilator, a situation that Joseph Smith found untenable: “Your plan of ventilation appears plausible,” he wrote Ericsson, “but sailors do not fancy living underwater.” 50   Yet underwater living is what Ericsson had in mind; even the toilets (four of them) had to be specially rigged with two valves and an air pump in order to flush while submerged. The operation was a bit tricky – the sea valve had to be closed when actually using the toilet, but to flush, the upper valve first had to be closed and the sea valve opened before engaging the (presumably hand-powered) air pump.  According to Ericsson’s biographer, William Church, a ship’s surgeon who had forgotten to close one valve, presumably while sitting on the toilet, “found himself suddenly projected into the air at the end of a column of water rushing up from the depths of the ocean and pouring into the ship.” 51    

Line engraving published in Harper’s Monthly, Volume 25, September 1862, page 433, depicting the launching of the ship at the Continental Iron Works, Greenpoint, New York, on 30 January 1862. (NHHC Photo # NH 604)

By mid-February the various pieces of the hull, turret, and machinery had been brought together and assembled at the Green Point shipyard. But before Monitor could be called an integrated weapon system, the crew had to bring those separate parts to life and make them work as one unit.   

Performance of USS Monitor during her ten-month service life    

Monitor was launched on January 30, 1862.  Construction of the turret and other fitting out took another two weeks. On February 19, the commanding officer, Lieutenant Worden, took possession of the ship for trials. That same day, Worden received orders from Gideon Welles to proceed with his ship, not even completed, to Hampton Roads. The haste was due to the fact that Welles received intelligence that two days earlier, Merrimack (sic, CSS Virginia, though Welles and most of the Union apparently did not learn of the name change until much later) had been launched and now threatened the Union port of Newport News.

The ship trials uncovered a number of teething problems inherent in almost any new design.  The first shakedown cruise, a 2-mile trip down the East River to the Brooklyn Navy Yard, did not go well.  The Delamater Iron Works, in its haste to get the engines finished, had made the serious but easily reparable mistake of setting the steam cutoff valves for backing instead of ahead, so that the ship only made 3.5 knots instead of its promised 9 knots.  On February 25, Worden put the ship into commission and promptly ran into different troubles.  The rudder was of a balanced design that was still fairly new to iron shipbuilding. Sailing ship rudders were typically attached directly to the sternpost and hinged at their forward edge, a practice still common in newer steamships. Like all balanced rudders, Monitor’s rudder was hinged some distance aft of the forward edge, so that it could be turned more easily. However, rudder theory was almost non-existent in 1861, so there was little guidance on how to do this effectively.  Ericsson had placed the hinge post too far aft, with the result that it was over-balanced and swung wildly at the slightest command.  Ericsson imperiously but correctly decided against drydocking the ship to fit a new or modified rudder, as this would take several days — an eternity given that Virginia was already afloat and posing a grave threat to the Union navy.  He instead devised a different arrangement of the steering cables and pulleys to increase the leverage of the helmsman over the rudder.  In a second trial run on March 3, the ship made 7 knots and handled reasonably well, but the gunnery trials were marred by a misunderstanding by Alban Stimers of how the friction gear worked (he turned the handwheel on each gun the wrong way, loosening instead of tightening the compressor), so that both guns recoiled violently and bounced off the rear of the turret. 52

Far worse problems befell the ship on its maiden sea voyage. On March 6, Monitor was taken under tow to Hampton Roads to meet CSS Virginia. Stimers rode as a passenger, while Isaac Newton filled the position of engineer.  In calm water on the first day, the ship rode smooth and dry.  By the following day, heavy seas were pouring over the deck and into the ship. The worst flooding came from the gap between the hull and turret.  While Ericsson had designed the base of the heavy turret to create a metal-to-metal seal with the embedded brass ring on the deck, Stimers had ordered the turret jacked up and the gap stuffed with oakum caulking (a wooden ship practice), much of which promptly washed away under the pounding of the waves. The pumps labored to dewater the ship, but their power source was also in danger of flooding.  Waves washed over the ventilation intakes and boiler funnel, so that the blowers became flooded and the leather drive belts slipped.  Starved of air, the boilers soon lost steam and acrid fumes filled the air throughout the ship.  The ship’s executive officer, Lieutenant Samuel Greene, signaled the tug to pull towards to shore. Five hours later, in calmer waters, Stimers, Newton and the engineering crew repaired the blowers and brought up steam to recommence the trip to Hampton Roads.  It was now apparent that the ship’s Achilles heels were the ventilation and funnel arrangements, but there was nothing to be done before the upcoming battle. 53

Monitor arrived in Hampton Roads the evening of March 8. Worden soon learned that Virginia had already destroyed the Union sail frigates Cumberland and Congress, while the steam frigate Minnesota ran aground early in the battle and remained stranded throughout. Virginia could not attack Minnesota before nightfall because of the tides, so withdrew shoreside to await the dawn and the chance to destroy Minnesota. In the middle of the night, however, Worden brought Monitor alongside the steam frigate to stand guard.  About 8:30 am the next morning, Sunday March 9, as CSS Virginia approached USS Minnesota, Worden brought USS Monitor to intercept and fired the first shots of the running duel. With political figures like Gustavus Fox (Assistant Secretary of the Union Navy) looking on, the two ships exchanged gunfire for almost four hours. Monitor fired solid shot while Virginia fired shells, though neither shot nor shell had much effect on either ship. Monitor was more maneuverable and avoided a ramming attack, while Worden was able to bring her guns to bear on Virginia’s vulnerable stern (but missed the screw and rudder).   

As a completely new, never-before-tried weapon system, Monitor and its crew performed reasonably well during battle. Operational command was hampered by the fact that the speaking tube between the pilot house and the turret was disabled early on, so runners had to carry messages back and forth, which took precious time. The turret itself was hard to control, its inertia making it slow to start turning and difficult to stop. Moreover, sighting the guns was made difficult by the enclosed arrangements with only a tiny line of sight through the gunports or a tiny viewing port. The gun crew lost its bearings and did not always know which way the turret was aimed. They could not point the guns directly forward or aft as the blast could disable the pilot house or ventilation intakes. The pendulated gunport stoppers were hard to manhandle and interfered with the guns, so that only one gun could be run out at a time.  Nevertheless, the crew quickly adapted to the circumstances, and after only a brief lull to resupply with ammunition, Monitor fought Virginia to a draw.  By noon, both ships had sustained minor damage, which forced their commanders to temporarily sheer off to assess the situation. Each commander then assumed the other ship had withdrawn from battle, and the fighting stopped. Worden was the only casualty, temporarily blinded from a shell that struck the pilothouse and exploded. Monitor herself was dented and scarred, but otherwise still battle-ready.  Although tactically a draw, the battle prevented the Confederate Navy from fully occupying Hampton Roads and the James River, and was generally seen as a strategic victory for the Union Navy. 54

Battle of Hampton Roads (NHHC Photo # 1053)

Both Virginia and Monitor remained in the Hampton Roads area, both sides itching for a rematch.  Neither side knew it at the time, but the March 9 battle would be the last ship-to-ship battle they ever fought.  On April 11, Virginia sortied into the roadstead, but Monitor stayed near Fort Monroe and the two simply exchanged a few desultory rounds.  On May 8, as part of a larger Union assault on the Confederate positions in Norfolk, Monitor and several other Union warships bombarded the Confederate battery at Sewell’s Point.  Virginia sortied to confront them, but the Union warships retreated.  Several days later, as Union troops occupied Norfolk, CSS Virginia was burned and sunk by its own crew to avoid falling into enemy hands.

The destruction of CSS Virginia and capture of Norfolk meant that Monitor could be released for other duties.  On May 15, a squadron of ships, including the ironclads USS Monitor, USS Galena (recently put into service) and USRC Naugatuck (originally built as a proof-of-concept ship for the Stevens Battery) steamed up the James River to test the defense of the Confederate capitol, Richmond.  At a bend in the river several miles outside the city, the fort at Drewry’s Bluff defended the river. The flotilla could not negotiate the turn, and anchored near the base while shot and rifle fire rained down upon them.  Monitor’s gun mounts, which were designed and built to aim at other ships and coastal batteries in near-flat trajectories, could not elevate sufficiently to hit the batteries on the bluffs 90 feet above the water.   When she backed off to decrease the angle of fire, the guns were unable to reach the batteries.  Monitor’s 1-inch deck armor protected it from damage, while Galena, with just .5-inch deck armor, suffered greatly from the falling shot.  After this, the flotilla retreated downriver. 55

For most of the summer of 1862, Monitor lay idle while defending the James River, its boiler continually making steam in case of a fight.  The combination of the boiler’s heat and the summer sun baking down upon the black iron hull made conditions inside unbearable, reaching 150 degrees Fahrenheit in some spaces.  In September, the ship was ordered to the Washington Navy Yard for an overhaul.  While in drydock, the hull was scraped and the engines repaired, after which (as noted earlier) Isherwood ran tests on their efficiency.  A permanent smokestack and taller ventilation boxes were fitted, which improved efficiency and reduced the potential for downflooding.  By November, the ship was back in Hampton Roads for guard duty.

Monitor’s final voyage began under tow on December 29, 1862 with the destination of Beaufort, North Carolina to assist in the blockade of Wilmington.  Lieutenant Samuel Greene, who had experienced the harrowing trip from New York to Hampton Roads back in March, was appalled at the idea of another ocean voyage: “I do not consider this steamer a seagoing vessel,” he said, complaining about its lack of horsepower and continued trouble with steering.  Those issues, however, would not be Monitor’s undoing.  Once again, the problems lay in the turret and ventilation arrangement. Although every opening was sealed, once again the turret was jacked up and oakum caulking stuffed underneath, where Ericsson specifically designed the turret / deck mating seal to be watertight.  On the second day, the ships were off the coast of Cape Hatteras when the seas began to rise. The ship yawed and rolled sickeningly, as waves swept over the deck and washed away portions of the oakum. Water poured into the gaps between the turret and hull, dampening the coal and furnaces.  The pumps could not keep up with the inrush, and water now entered the ventilation ducts, disabling the blowers as well. By midnight the boilers gave out, and the order was given to abandon ship. Around 1:00 am the morning of December 31, 1862, the ship foundered with sixteen men lost. 56   From commissioning to sinking, USS Monitor was in active service only ten months. During that short existence, Monitor and her crew had accomplished more than many warships achieve in ten or even thirty years. By stopping CSS Virginia’s attacks and holding her at bay through the spring and summer of 1862, USS Monitor also stopped the Confederate advance through Hampton Roads and made possible the Peninsular Campaign.  She also changed the face of naval warfare for a generation.    

The influence of Monitor on warship design and construction, 1862-1898

As stated earlier, Ericsson’s greatest “contrivance” with the respect to Monitor was the invention of the need for a slow, shallow-draft, mobile coastal battery in a previously blue-water navy.  That perceived need had not existed before Monitor demonstrated her performance at Hampton Roads; not only the original request for bids, but even the Union Navy’s contract with Ericsson, stipulated that the vessel should be rigged for ocean cruising.  After the battle with Virginia, that viewpoint completely changed.  Gideon Welles, Gustavus Fox, and the Union Navy’s political establishment, as well as the wider public, saw Monitor as “completely invincible,” believing that the victory at Hampton Roads was the decisive battle that pointed the way to the design of the future fleet.  Charles Cramp, builder of New Ironsides, bitterly referred to this as the “Monitor Craze” and argued that by fixating on the turreted shallow-draft monitor, it put a stop to any further developments in Union naval ship design. In the years 1862 and 1863, the Union Navy contracted for fifty-seven monitors, of which fewer than half actually served during the war. At the same time, the Union Navy constructed only a handful of casemate ironclads similar to New Ironsides and Galena. 57

Immediately after Hampton Roads, Gustavus Fox ordered Ericsson to design new classes of monitors.  The first was the Passaic class, whose lead ship was commissioned in November 1862.  Though most of the major systems were similar to those of Monitor (e.g., spindle turret, double-trunk engine), Ericsson incorporated lessons learned from the battle: larger-caliber guns (XV-inch vis XI-inch), pilot house atop the turret for easier communication with the gun crew, rotating vice pendulated gunport stoppers (which he patented), and better steering. However, Ericsson and the Union Navy did not fully recognize the downflooding problems until after Monitor sank, so it was not until Ericsson’s next designs, the Canonicus class (single turret) and Miantonomoh class (double turret), that improved ventilation and funnel arrangements were incorporated.  Meanwhile, Alban Stimers took charge of the shallow-draft Casco-class monitors, which were widely seen as failures. 58    

The rapid naval drawdown after the Civil War reduced the US Navy to a primarily coastal presence, in which monitors fit perfectly.  One of the few shipbuilding programs in the 1870s produced the Amphitrite class of breastwork (i.e., raised central deckhouse) monitors, whose ships still had muzzle loading guns and Ericsson’s central-spindle turrets, but which were equipped with the latest engines designed by Benjamin Isherwood.  By 1883, the widespread adoption of breech-loading guns put paid to Ericsson’s central-spindle turret, and all future American turrets were built along the Coles roller bearing design. 59   Just at this time, the new American fleet of steel cruisers (the ABCD ships) was being laid down in Philadelphia, which signaled the ended of the coastal fleet and the beginning of a more muscular ocean-going presence.  The last of the US coastal monitors, the Arkansas class, was built in 1898 for the Spanish American War.        

The “Monitor Craze” was not confined to the United States.  After the Battle of Hampton Roads, Monitor-type turreted ironclads were widely sought for coastal defense in European and Latin American nations.  Britain and France, the two major naval powers, weighed the merits of seagoing versus coastal ironclads.  In Parliament, the debates were fierce; advocates of the former pointed out that Monitor barely survived its maiden voyage, while devotees of the latter pointed out that Britain could build six Monitors for the price and schedule of one Warrior.  In the end, both Britain and France hedged their bets by continuing to build oceangoing armored warships, while also investing in coastal defense; in the twenty years after Hampton Roads, they constructed twenty-eight coastal defense vessels and rams, including ten monitors, compared with fifty-three oceangoing ships. For the smaller naval powers, Monitor proved the model for the relatively inexpensive, cost-effective alternative to the conventional battleship. 60

Most ironclad monitors built for smaller Europe and Latin America navies were constructed in Britain and France, and all had Coles-type turrets.  The first to enter service was the British-built ironclads Rolf Krake (to Denmark) in 1863 and Huáscar (to Peru) in 1865.  These were followed in 1868 by a pair of breastwork monitors (Cerberus class) for British colonies, and the Schorpioen and Buffel, both built in France for the Netherlands. Ironically, John Ericsson benefitted very little from the Monitor craze.  Only Russia and his mother country of Sweden ordered ships from him, both of which were versions of the Passaic class.  In Russia, the ship became known as the Uragan class.  In Sweden, they were named the John Ericsson class after their designer.  Ericsson supervised the designs while in the United States, and the plans were brought back to their nations by naval attachés who also oversaw their construction. 61

At the same time that Britain was building coastal monitors, the Royal Navy also launched the first ocean-going turreted warship, HMS Monarch (1868), which set the stage for the modern battleship.  The construction of Monarch did not sit well with Cowper Coles, as the Royal Navy had selected it over his own design.  Coles successfully lobbied Parliament to fund construction of his own low-freeboard turret monitor, which was commissioned as HMS Captain in April 1870.  Five months later, Captain foundered and sank in a storm due to inadequate stability, taking Coles and almost 500 other men with her.          

The Monitor craze did not of course end all at once after the sinking of HMS Captain, but the growing belief that long-range oceanic capability was imperative for both established and emerging naval powers led to the rise of the ocean-going battleship and pushed coastal monitors to eventual extinction.


During the desperate beginnings of the Civil War, USS Monitor was designed, built and delivered in less than six months, just in time to stop CSS Virginia, an existential threat to the Union Navy.  Ericsson had envisioned his ship for the Crimean War, yet he convinced the Washington establishment that it would be the right ship for the Hampton Roads campaign.  In fact, USS Monitor was, as stated, the wrong ship at the right time, a brown-water ship designed for a blue-water navy.

The fact that Ericsson had been thinking about this new system of naval warfare for so long meant that he had a clear vision of what it should be almost as soon as the request crossed his desk.  He conceived of the ship and its components as part of an integrated system, everything bent to the purpose of ship-to-ship or ship-to-shore warfare.  His great genius, however, was to understand that such a novel ship could be built only with tried-and-tested technology and a trusted network of collaborators. Contrary to legend, almost nothing aboard Monitor had not previously been built and tested in service. Ericsson limited the suppliers to men he knew or knew he could trust to obtain vital resources, notably iron, in a time of war-driven scarcity.    

Monitor’s success at Hampton Roads resonated across the globe, convincing not only the Americans but also many Europeans that turreted coastal ironclads were the ships of the future.  This mindset lasted almost a generation, before the battleship replaced the monitor in the popular and professional imagination.          

(Return to May 2021 Table of Contents) 


  1. John S.C. Abbott.  The History of the Civil War in America, 2 vols. (Springfield, Massachusetts:  Gurdon Bill, 1863-1866), vol. 1 p. 340; William Conant Church, The Life of John Ericsson, 2 vols. (New York: Scribner’s, 1890), vol. 1 p. 261; and most recently Richard Snow, Iron Dawn: The Monitor, the Merrimack and the Civil War Sea Battle that Changed History (New York: Scribner, 2016), pp. 125-127.  For an early example of an uncritical citation of “forty patentable contrivances,” see Martha J. Lamb, “John Ericsson, the Builder of the Monitor 1803-1889,” Magazine of American History 25/1 (1891), pp. 1-17, at p. 12.
  2. “Ericsson Battery – Interesting Statement from the Inventor,” Chicago Tribune (March 17, 1862), p. 4.
  3. Donald L. Canney.  The Old Steam Navy, Volume One:  Frigates, Sloops and Gunboats, 1815-1885.  (Annapolis, Maryland:  Naval Institute Press, 1990), p. 46; Quotes from Charles W. MacCord, “Ericsson and His Monitor,” The North American Review, 149/395 (1889), pp. 460-471, at p. 461; and Howard J. Fuller, Clad in Iron: The American Civil War and the Challenge of British Naval Power (Westport, Connecticut: Praeger, 2008) p. 61.  Ericsson’s patented inventions that found a home on USS Monitor include: Propelling Steam Vessels, US Patent 588 of 1838; Improvement in Propelling Ships, US Patent 3,869 of 1844; Screw Propeller, US Patent 4,181 of 1845; Steam Engine, US Patent 6,255 of 1849; and Improvement in Steam Engines, US Patent 20,782 of 1858. He did not use the Apparatus for Distilling Sea-Water, US Patent 6,815 of 1849.
  4. Isaac Newton, “Shot-Proof Vessels – Ericsson’s Battery,” Journal of the Franklin Institute 73 (3rd Series, vol. 43) (1862), pp. 73-82; “Ericsson Battery – Interesting Statement from the Inventor.”
  5. David P. Hollway, Report of the Commissioner of Patents for the Year 1863, 2 vols. (Washington, DC: Government Printing Office, 1866), vol. 1 p. 42.  Ericsson’s post-Monitor patents:  Improved Port-Stopper for Vessels of War, US Patent 40,830 of 1863; Operating Gun Carriage, US Patent 40,919 of 1863.
  6. Craig L. Symonds, The Civil War at Sea (Santa Barbara, California: Praeger 2009), p. 7.
  7. Quoted in Fuller, Clad in Iron, p. 46.
  8. Quoted in Adolph A Hoehling, Thunder at Hampton Roads (New York: Da Capo Press, 1993), p. 41.
  9. For accounts of Ericsson’s inventions in Britain, see “Capt. John Ericsson, the Designer and Builder of the Iron-clad Battery Monitor,” New York Illustrated News (March 29, 1862), p. 329; Philip W. Bishop.  “John Ericsson (1803-89) in England,” Transactions of the Newcomen Society 48 (1977-78), pp. 41-52; and Andrew Lambert, “The Royal Navy, John Ericsson and the Challenges of New Technology,” International Journal of Naval History, 2/3, (2003), accessed November 2018. See also Albert E. Seaton, The screw propeller: and other competing instruments for marine propulsion (London: C. Griffin & company, 1909).
  10. Alligator was lost under tow off Cape Hatteras in March 1863, just months after Monitor was lost under tow in the same area. See Chuck Veit, Natural Genius: Brutus de Villeroi and the US Navy’s First Submarine (Morrisville, North Carolina:, 2018).
  11. On the naval technology employed during the Crimean War, in particular at the Battle of Kinburn, see James Phinney Baxter, The Introduction of the Ironclad Warship (Cambridge, Massachusetts:  Harvard University Press, 1933), ch. 5; Marine et technique au XIXe siècle (Vincennes: Service Historique de la Marine, 1987), parts 2 and 3; Robert Gardiner (ed.), Steam, Shell and Gunfire: The Steam Warship 1815-1905 (London: Conway, 1992), ch. 3; Jack Greene and Alessandro Massignani, Ironclads at War: The Origin and Development of the Armored Warship, 1854-1891 (Conshohocken, Pennsylvania:  Combined Publishing, 1998), ch. 1, quote at p. 30.
  12. Cowper P. Coles, Apparatus for Defending Guns &c, UK Patent 798. March 30, 1859; Coles, Iron-Cased Ships of War, UK Patent 1,462.  June 15, 1860; Cowper P. Coles, “Cupola Ships,” The Times [of London
  13. See Lee M. Pearson, “The ‘Princeton’ and the ‘Peacemaker’: A Study in Nineteenth-Century Naval Research and Development Procedures,” Technology and Culture 7/2 (1966), pp. 163-183.
  14. Report of the Secretary of the Navy in Relation to Armored Vessels (Washington, DC:  Government Printing Office, 1864), p. 13; John Ericsson, Contributions to the Centennial Exhibition (New York: The Nation Press, 1876), pp. 410-416.  Ericsson was already well known to the French Navy, having supplied (under license) the engines and propeller of the frigate Pomone in 1847.  Ericsson stated that he received a gracious reply from Napoleon III”s aide-de-camp, Ildephonse Favé, who was also an artillery officer.  Researchers have found no surviving records of the reception and evaluation of Ericsson’s proposal (or Favé’s reply) in any French archives (Baxter, The Introduction of the Ironclad Warship, pp. 184-185, and archival searches by myself and French historian Alexandre Sheldon Duplaix). Given that Ericsson produced the memo only when there was some question of whether he or Cowper Coles had invented the revolving turret, it is possible that Ericsson back-dated his proposal to support his priority dispute.
  15. Jeffrey Remling, “Patterns of Procurement and Politics: Building Ships in the Civil War,” The Northern Mariner/Le marin du nord 17/ 1 (2008), pp. 16-29.
  16. “Report of the Naval Board on the Stevens Battery,” Journal of the Franklin Institute 73 (3rd Series vol. 43) (1862), pp. 149-162.  The Stevens Battery was never completed, and was eventually scrapped in 1881.
  17. Report of the Secretary of the Navy in Relation to Armored Vessels, 1-2; Measuring Worth: Purchasing Power of Money in the United States from 1774 to Present,, accessed July 2018.  When comparing large government outlays for programs such as the Ironclad Board program, economists use the GDP (Gross Domestic Product) deflator instead of the CPI (Consumer Price Index) deflator.  That means the cost of the program is compared as a percentage of the nation’s GDP, instead of a CPI basket of goods like homes and bread.  Since GDP rises much faster than CPI, the figures appear more striking but are more accurate.
  18. Charles B. Boynton, The History of the Navy during the Rebellion, 2 vols. (New York: D. Appleton, 1867-68), vol. 1 p. 21; and Fuller, Clad in Iron, passim.
  19. Report of the Secretary of the Navy in Relation to Armored Vessels, p. 2.
  20. Anna Gibson Holloway and Jonathan W. White, “Our Little Monitor“: The Greatest Invention of the Civil War (Kent, Ohio: Kent State University Press, 2018), p. 25.
  21. Report of the Secretary of the Navy in Relation to Armored Vessels, pp. 3-7.  Among the rejected proposals was one for a quadruple-gun ironclad by Ericsson’s Swedish countryman, John W. Nystrom.
  22. Robert J. Schneller, Jr.  “The Battle of Hampton Roads, Origins of Ordnance Testing against Armor, and U.S. Navy Ordnance Development during the American Civil War,” International Journal of Naval History 2/3, (2003), accessed November 2018.
  23. Barbara B. Tomblin. From Sail to Steam: The Development of Steam Technology in the United States Navy 1838-1865, unpublished PhD dissertation (New Brunswick, New Jersey:  Rutgers University, 1988), pp. 224-225.
  24. See William H. Roberts, USS New Ironsides in the Civil War (Annapolis, Maryland: Naval Institute Press, 1999).
  25. James Tertius deKay, Monitor: The Story of the Legendary Civil War Ironclad and the Man whose Invention Changed the Course of History (New York: Walker, 1997); William H. Roberts, Civil War Ironclads:  The US Navy and Industrial Mobilization (Baltimore, Maryland:  Johns Hopkins University Press, 2002.); and Remling, “Patterns of Procurement and Politics”; Quote: Report of the Secretary of the Navy in Relation to Armored Vessels, p. 7.
  26. John Ericsson, “The Building of the Monitor”, in Robert Johnson and Clarence Buel (eds.), Battles and Leaders of the Civil War, 2 vols. (New York: The Century Company, 1887), vol. 1 pp. 731-744.
  27. Report of the Secretary of the Navy in Relation to Armored Vessels, p. 5, p. 8.
  28. The original USS Monitor Contract Specifications are in the National Archives and Records Administration (hereafter NARA) RG 45 entry 502 (subject files 1775-1910) AD box 51 folder 10.  It is reprinted in William S. Wells (ed.), The Original United States Warship “Monitor” (New Haven, Connecticut: Cornelius S. Bushnell National Memorial Association, 1899), pp. 30-33.
  29. For descriptions of Monitor’s layout, see Donald L. Canney, The Old Steam Navy, Volume Two:  The Ironclads, 1842-1885 (Annapolis, Maryland:  Naval Institute Press, 1993), pp. 25-34; and deKay, Monitor, pp. 90-93.
  30. The manufacturing companies of Monitor are discussed in William N. Still, “Monitor Companies: A Study of the Major Firms that Built the USS Monitor,” American Neptune 48/2 (1988), pp. 106-130; Stephen C. Thompson, “The Design and Construction of USS Monitor,” Warship International 27/3 (1990), pp. 222-242; and Marcus R. Cimino, “The Construction of USS Monitor and its impact on the Upper-Hudson Valley” LINK.
  31. Years later, the city of Nashua, New Hampshire, erroneously laid claim to these port stoppers, even erecting a bronze marker at the former site of the Nashua Iron and Steel Works, stating that the Works forged the stoppers. This is not supported by the contemporary records, all of which clearly show Niagara Steam Forge as the manufacturer. The first mention of the Nashua myth is from the end of the 19th century. See Edward E. Parker, History of the City of Nashua, N. H.  (Nashua, New Hampshire: Telegraph Publishing, 1897), p. 440.
  32. Remling, “Patterns of Procurement and Politics”, p. 24; “The U.S.S Armored Frigate New Ironsides,”   Journal of the Franklin Institute 79 (3rd Series vol. 53/2) (1867), pp. 73-81.
  33. Ernest W. Peterkin, Drawings of the USS Monitor. A Catalog and Technical Analysis, U.S.S. Monitor, Historical Report Series 1/1 (Washington, DC: NOAA, 1985), p. 12.
  34. Dana M. Wegner, Alban B. Stimers and the Office of the General Inspector of Ironclads, 1862-1864, unpublished Master’s thesis (Oneonta, New York:  SUNY Oneonta, 1979), p. 22; Washington Jones, “Some Recollections of Machine Shops in the Early Forties,” The American Machinist 19/18 (1896), p. 452.  For early biographical information on Ericsson, see: Church, The Life of John Ericsson; and Lamb, “John Ericsson, the Builder of the Monitor”.
  35. On drawing practices of the era, see John K. Brown, “Design Plans, Working Drawings, National Styles: Engineering Practice in Great Britain and the United States, 1775-1945,” Technology and Culture 41/2 (2000), pp. 195-238. On Monitor’s contract oversight, see Alan P. Mayer-Sommer, “A Historical Case Study of Planning and Control Under Uncertainty: The Weapons Acquisition Process for the US Ironclad Monitor,” Journal of Accounting and Public Policy, 7/3 (1988), pp. 201-249. On its construction oversight, see Wegner, Alban B. Stimers.
  36. USS Monitor Contract Specifications, and Ericsson to Joseph Smith, October 2, 1861, both in NARA RG 45 entry 502 AD box 51 folder 10.  The Union Navy did not provide final acceptance until after the Battle of Hampton Roads, which is when Ericsson received his final payments (Holloway and White, “Our Little Monitor“, p. 44).
  37. David A. Mindell, War, Technology and Experience aboard the USS Monitor (Baltimore, Maryland:  Johns Hopkins University Press, 2000), p. 121.
  38. Church, The Life of John Ericsson, vol. 1 p. 240.
  39. Schneller Jr., “The Battle of Hampton Roads”.
  40. Peterkin, Drawings of the USS Monitor, pp. 46-49, pp. 500-509; deKay, Monitor, pp. 123-124.
  41. R.A.E. Scott, “Modern Carriages for Heavy Naval Ordinance”, Journal of the Royal United Service Institution 10/41 (1866), pp. 496-516; Peterkin, Drawings of the USS Monitor, pp. 510-531; Church, The Life of John Ericsson, vol. 2 p. 144;  personal correspondence from David Krop, Mariner’s Museum, September 2013; John Ericsson, Operating Gun Carriage, US Patent 40,919 of 1863.
  42. Canney, The Old Steam Navy, Volume Two: The Ironclads, p. 30; deKay, Monitor, p. 108.
  43. Cowper P. Coles, English versus American Cupolas: A Comparison Between Captain Coles’ and Captain Ericsson’s Turrets (Portsea, Portsmouth: J. Griffin, 1864); Arnold A. Putnam, “The Introduction of the Revolving Turret,” American Neptune 56/2 (1986), pp. 17-129; Putnam, “The Eads Steam-Powered Revolving Turret,” Warship International 42/3 (2005) pp. 303-317; Theodore R. Timby, Revolving Battery Tower, US Patent 35,846, July 8, 1862; deKay, Monitor, pp. 92-93.
  44. Marine et technique au XIXe siècle, 37; Norman S. Russell, “Iron Armour for Ships of War,” Proceedings of the Institution of Mechanical Engineers 13/1 (1862), pp. 289-326.  See also John H. Morrison, “The Development of Armored War Vessels: Armor Plating in the United States,”  Scientific American Supplement 64 (July-Dec 1907), passim; and Roberts, USS New Ironsides in the Civil War, p. 21. Later tests (1868) by the British Ordnance Select Committee indicated that laminated armor was more effective than the simple “square of thickness” theory predicted so that five laminated 1-inch plates would be far more than ‘40 percent’ as effective as a single 4.5-inch plate and was in fact closer to 78 percent, or the equivalent of a solid 3.51-inch plate; thus the original Monitor’s eight 1-inch plates were closer in resistance to a solid 6.21-inch plate—though not also not counting the added strength of a curved turret-plate structure versus a flat slab of broadside armor (personal correspondence from Howard Fuller, November 2013).
  45. Correspondence between Ericsson and Joseph Smith, January-February 1862, NARA RG 45 entry 502 AD box 51 folder 10.
  46. Baxter, The Introduction of the Ironclad Warship, pp. 264-266; Fuller, Clad in Iron, p. 58.
  47. Benjamin Isherwood, Experimental Researches in Steam Engineering. 2 vols. (Philadelphia, Pennsylvania: William Hamilton, 1863-1865), vol. 1 pp. 330-340.
  48. Isherwood, Experimental Researches.
  49. Andrew Lambert, Warrior: Restoring the World’s First Ironclad (London: Conway, 1987), pp. 108-109; On the steam machinery of both naval vessels and passenger / mail steamers like the Collins Line, see Frank M. Bennett, The Steam Navy of the United States (Pittsburgh, Pennsylvania: Nicholson, 1896).
  50. Smith to Ericsson, October 16, 1861, John Ericsson Collection, American Swedish Historical Foundation Microfilm Edition (Philadelphia, Pa), Reel 4.
  51. Peterkin, Drawings of the USS Monitor, p. 176; Church, The Life of John Ericsson, vol. 1 p. 261.
  52. deKay, Monitor, pp. 123-137. On modern rudder theory, see Edward V. Lewis (ed.), Principles of Naval Architecture, 3 vols. (Jersey City: SNAME, 1988), vol. 3 ch. 9.
  53. deKay, Monitor, pp. 138-149; Mindell, War, Technology and Experience aboard the USS Monitor, pp, 61-69.
  54. deKay, Monitor, pp, 173-198; Mindell, War, Technology and Experience aboard the USS Monitor, pp. 70-86; Howard J. Fuller, “John Ericsson, the Monitors and Union Naval Strategy,” International Journal of Naval History, 2/3, (2003) accessed November 2018.
  55. Mindell, War, Technology and Experience aboard the USS Monitor, pp. 95-98.
  56. deKay, Monitor, pp. 215-219.
  57. Tomblin, From Sail to Steam, p. 306; Roberts, Civil War Ironclads, p. 23.
  58. Wegner, Alban B. Stimers.
  59. Naval Advisory Board, Executive Documents for the Second Session of the Forty-Seventh Congress, (January 11, 1883), p. 33.
  60. Howard J. Fuller, Empire, Technology and Seapower: Royal Navy crisis in the age of Palmerston (London: Routledgem, 2013), pp. 229-230; Robert Gardiner (ed.), Conway’s All the World’s Fighting Ships 1860-1905 (Annapolis, Maryland: Naval Institute Press, 1979), pp. 13-30, pp. 288-300; Carlos Alfaro Zaforteza, “The collapse of the Congress System, 1854–1870,” in Carlos Alfaro-Zaforteza, Alan James, Malcolm H Murfett, European Navies and the Conduct of War (New York: Routledge, 2018), pp. 113-129, at p. 124.
  61. Daniel G. Harris, “The Swedish Monitors“, in John Roberts (ed.), Warship 1994 (Annapolis, Maryland: Naval Institute Press, 1994), pp. 22-34; Jan Glete, “John Ericsson and the Transformation of Swedish Naval Doctrine,” International Journal of Naval History, 2/3, (2003) accessed November 2018.

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