A note on the Ironclads
I love the look of the American Civil War ironclads

CSS
Virginia & USS
Monitor, both launched in 1862.
Bigger version of picture.One of the ideas behind their development, was to make it harder for the enemy ships to actually hit them. From memory,
Virginia was built so enemy fire would 'slide off' and with
Monitor, there is obviously little above the water to target.
USS Monitor obviously gave its name to the line of warships to come. although the very low deck obviously created problems at sea, which the breastwork monitor was developed to overcome.
To put these mastless, iron beasts into a ship-building context, this is still the era of the clipper ships, with the
Cutty Sark still a few years from being built, and sail driven traders like
Polly Woodside were still being built decades later.
Before the monitors though, there was the British
HMS Warrior, launched 1860 and the first ocean going ironclad, the French
La Gloire, launched 1859. I believe
La Gloire was a wooden-hulled warship plated with iron, enough to make the traditional wooden warships suddenly obsolete. She in turn was made obsolete with the launching of
Warrior just over a year later.
Warrior was built with iron plates and had a single, central gun citadel, replacing the traditional rows of gun decks. While I don't think she ever saw active service, she was the start of an almost century-long naval arms race.