The evolutions of the ironclad into the battleship took place over the course of the course of the 1860s to ~1890. At the start of this period, we find fleets composed mainly of broadside and central-battery ironclads, much resembling the ships of the line of the age of sail, with only a few turreted ships. At the end of the period, the first pre-dreadnoughts were coming into service.

The first ironclads were built to the general plan of the wooden frigates that proceeded them, with their armament along their broadsides, but with added armour. Some were even just wooden ships armoured while building. The addition of armour required a change in armament; to penetrate the armour required large guns. These guns were too heavy to carry along a full broadside while also carrying a reasonable amount of armour. With a traditional design that wasn't carrying a full broadside, there were many angles down which no gun could be brought to bear. To solve this problem, two main concepts were put forward. The simplest was the central-battery ship. These carried their few main guns on pivoting mounts in the centre of the ship, with gunports pointing in multiple directions. This also allowed for a concentration of the heaviest armour over the battery. The other option was to put the gun on a rotating mount on the deck. This could either be a turret, at this time essentially an armoured box, or a barbette, a rotating platform typically surrounded by a stationary ring of armour. Barbettes were easier to engineer and lighter, but did not give overhead protection; turrets were more protective, but were so heavy that ships with them tended to have dangerously low freeboard (the distance between the water and the ship's deck). Barbettes were preferred by the French, while turrets were generally preferred by British builders. Neither were really practical for long-range ships, though. In the 1860s, steam engines were too primitive to allow them to be used for long periods of time - they burned too much coal, and were too unreliable - so ships intended for long voyages had to carry sailing rig as well. The masts and rigging blocked the arcs of fire of guns mounted in barbettes and turrets, while the risk of fire in the rigging from muzzle blast was ever-present. During the American Civil War, though, fought in littoral and riverine waters, there was no need for long voyages, and so ironclads could be powered by steam alone. This allowed turreted ships in particular to thrive.

The main contribution of American designers to the world of naval architecture in the 1860s was the concept of the monitor. Named after the first such vessel, which fought for the Union at the 1862 Battle of Hampton Roads, this was essentially an armoured, steam-powered raft with a turret on top. Monitors were excellent ships for coastal defence - their low freeboard made them hard targets, but prevented them from making trips on the open ocean due to the risk of being swamped by the waves, while they could carry heavy guns in their turrets. British designers liked the capabilities that the monitor offered, but wanted ships less vulnerable to flooding. This was especially necessary because the Coles-type turrets used by the RN (which were supported at the edges) provided more flooding paths than the Ericsson turrets used by the USN (which were supported by a spindle in the middle). To solve this problem, they came up with the concept of the breastwork monitor. This added a small armoured deckhouse to the armoured raft of the monitor, which the turrets, funnels and other openings were placed on top of. The first of these was the Cerberus, built in 1867 for the Australian state of Victoria. The breastwork monitor was highly influential, with many being built over the following years. In 1871, the RN applied this concept to a battleship, rather than a coastal defence ship, producing a large vessel with two twin turrets, one at either end of the breastwork, and enough range to sail from Ireland to Canada, named the Devastation. She was well-regarded within the navy, and a follow-on ship, Dreadnought was soon ordered. Dreadnought was redesigned while under construction, bringing the breastwork out to the edge of the ship and adding more freeboard to make a more seaworthy vessel. Most ships designed over the following decade for the RN, though, were influenced by the design of Inflexible, ordered at much the same time. She had a hull with high freeboard, which dipped down in the middle of the ship to form a well for the turrets to sit in.

In 1880, worried by new French construction, the RN began looking for a new paradigm. They found this by combining the French barbette concept with the general layout of Dreadnought, to form the 'Admiral' class, beginning with HMS Collingwood. The use of barbettes allowed the armament to be mounted high in the ship, letting it be used in heavy seas. However, their freeboard was still a bit too low to allow them to be good seaboats. They were still successful, highly influential ships. As the 1880s progressed, new technologies became available. Quick firing guns, which used breech loading and propellant cartridges to achieve a high rate of fire, were the most important of these. These guns could fire 5-7 times a minute, while the heavy guns used on the 'Admiral's might fire one round every two minutes at best. However, they fired a considerably smaller shell - the main QF gun used by British battleships was a 6in gun, while the 'Admiral's main armament were 12in guns. The QF gun could not penetrate the armour of the typical battleship. However, firing high explosive shells, they could swiftly wreck the unprotected superstructure and ends. The RN combined the 'Admiral's with the 6in QF gun to produce the Royal Sovereign class in 1888-9. These had improved freeboard over the 'Admiral's, the same primary armament, and a secondary armament of ten 6in QF guns. They were the first pre-dreadnought battleships; all others were improvements on the same formula.