The first ironclads were floating batteries, used by the British and French during the Crimean War. These were steam-powered vessels, armoured, and heavily armed, and used for attacking Russian forts. They were, however, not ocean-going ships. Their importance was more that they proved the concept for later work. In 1859, the French launched the first ocean-going ironclad, Gloire. This was quickly followed by the British Warrior. Both of these ships were typical frigates of the mid-19th century. They had masts and sails for strategic movement, and steam engines for use when the winds were unfavourable. They had armament mounted on their broadsides. Gloire was built with iron armour plates on wood, while Warrior's iron was more structural. Most ironclads that followed them in the 1860s were similar. There were two main variants, both seeking to solve the same problem: the guns needed to pierce armour were too heavy to carry on the broadside in large numbers. The central battery ship mounted a few guns in the centre of the ship, with sufficient gunports to allow all-round fire. The turret ship had one or two turrets, in which the heavy guns were mounted. The latter were, in theory, more capable. However, the high weight of the turrets, mounted high in the ship, combined with the masts and sails, made them unstable, and they were disfavoured following the capsize of HMS Captain in 1870. The American Civil War had little effect on the development of ocean-going ironclads, fought, as it was, on riverine and littoral waters. However, it did introduce the monitor. Essentially an armoured, steam powered raft, it was unseaworthy in its original configuration, but also clearly a capable craft. The Royal Navy, which needed ships to defend the far flung reaches of the British Empire, developed a modification to the design. The designers added an armoured breastwork on which the turret sat. Ultimately, this breastwork was extended to the edge of the hull, to form what would become the pre-dreadnought battleship.

There is a lot of info out there about the development of ironclads outside the US and the development of sea going ironclads.

During the Crimean war the need was found for shell proof vessels to engage Russian coast defence installations from close range. For that a self propelled mobile battery was needed. After some trials the protection was settled at 3,5 - 4 " rolled or (worse) hammered iron. In this war the French and British were allies and both devloped very similar vessels along these lines. Only the 3 of the French vessels were ready in time to participate in the war and they proved to be very useful: shellproof and due to their shallow draught able to close in to the fortresses and make their artillery very effective against brick revetments at that close range.

(note that these early batteries did look somwhat like the later CSS casemate vessels but with more gun ports)

Napoleon III sensed an opportunity here: if the French navy could combine the shell proof battery concept with that of a steam ocean going ship of the line, the French navy would gain a great advantage on its adversaries (the British again soon after the Crimean war).

Ans so it was done, the french desginer Dupuy de Lôme took the basic hull form and machinery of his 90 gun "Le Napoleon" class steam two deckers, added about 4" of armour on the wooden hull and reduced the number of guns drastically (and placed them on a single deck) to compensate for the extra weight. Thus the first ocean going ironclad "Gloire" was born. She was thus in most respects an armoured version of the earlier steam ships of the lines, and shared their squad somewhat squared off hull form.

The appearance of this ship caused somewhat of a stir in britain , whose wooden steam battlefleet was now compltely outclassed. As answer a sophisticated iron ship was produced, designed to take advantage of the extra structural strenght of the iron versus wooden hull and so HMS Warrior was born. HMS Warrior was not just an armoured version of the steam liner, she was a wholly new design, taken maximum advantage of the intricate strenght of an iron hull and had for example much finer lines than Gloire. Whereas Gloire could be seen as a step forward, HMS Warrior embodied a new concept of capital ship. (although superficially similar looking)

Both these ships were basically proof against hits from existing naval guns, but guns did evolve fast. Gloire had 2 sisters (and an iron hulled half sister) and was followed by a large class (10 ships) of nearly identical ships.

Warrior was followed up by a number of "product improved" ships, generally similar, but each with some imporvements (Achilles, the Minotaur class). As the cost of The Warrior type ships was very high, 4 diminutive versions were built. Altought the British navy tought they had a chance against Gloire type ships, the money saved in them did not justify the sharply diminished combat capabilitues.

Also due in another bit to save money, a number of 90 gun two deckers on the stocks were converted into ironclads which were surpirsingly succesful (Caledonia class, in several sub variants, converted from Bulwark class two decker ships of the line).

As guns grew heavier, the rahter thin armour of this first generation of ironclads became very vulnerable and ways were sought to improve the armour. On way was to armour only the central part of the ship and put fewer and larger guns in that armoured "box": box battery ships. Another way was to mount guns into rotating turrets (make no mistake, rotating armoured turrets were designed, build and tested in the UK before the famous Monitor).

The French favoured the "barbettte": an armoured stationary ring high up in the ship over the lip of which a heavy gun could fire on wide arcs.

The 1870'ies to 1890 were a period of experiment , the british navy buyilt a lot of ships, but almost always in ones or two's, each design was used as a sort of testing ground for new ideas and technology. The French navy was more uniform with a somwhat standardised design with a central box battery with barbettets mounted on top of that. But while the British quickly went over to the construction of iron ships only, the French continued to build wooden hulled ships, which were in a disadvantage due to their lower structural strenght and higer maintenance demands, the hulls also wearling out much more quickly. (some ships had only one or two active commisions).

From 1889-1890 we se in the britsh navy that Battleship designs were standardized: four heavy guns in "hooded" barbettes (later called turrets) distributed forward and aft and a batterly of light guns on the broad side. This standard design lasted until the coming of the dreadnought. Other navies tried other variations, but in the end almost everyone was building ships basically corresponding to the British design practice by say 1900.

How would a large naval conflict have happened ? The only really large naval conflict i can envision was between France and Britain given their large fleets in comparision to other countries. The French would concentrate on raiding using smaller armoured and unarmoured ships and the larger steam and sail ocean going ironclads and had a seperate fleet specifically designed for coastal defence. (and relied heavily on coastal defences) The British had ships to chase down the French ocean raiders (mostly the first genreration of ironclads, supported by some more modern desings with sail and steam power and unarmoured proto-cruisers, and also special ships (heavily armoured, with very heavy guns, often in a single turret firing forward) to penetrate the main French naval bases and destroy the ships in there. Note that this strategy of penetrating a defended enemy harbour was acutally trained at the time.

In short: the French had a doctrine (after say 1870) of coastal defence and commerce raiding using ships ranging from small wooden cruisers to their largest sail supported ironclads. (on this doctrine , see T. Ropp: The Birth of a Modern Navy) The British had ships to chase down the raiders (also ironclads with sails) and another line of ships specially designed to attack the French coast and especially penetrate the naval bases. (on this doctrine, see J. Beeler: the Birth of the Battleship, British Capital Ship Design 1870-1881)

note1: i have only discussed the French and British navies , since these were the main drivers for new technology in that era and with a substantial battlefleet.

note 2: i only describe the general evolution of the larger ironclads here, ships that would evolve in the later battleship. There were lots of experiments and designs of smaller armoured ships, down to one gunned armoured gun boats to use in the lagoons of Venice for example.

note 3. Any action larger then those involving a few ships on each side (and with smaller navies) would quickly desintegrate into a melée of single ship versus ship combats due to the restrictions of communication and command technology of the time, the enormous amount of smoke obscurig the battle and the very disparate designs of the ships and their optimal way of use in combat. Which is basically what happened at the Battle of Lissa.