At first glance these may look like boats, but "boats" is a loose term.. these were essentially just barges with large siege mortars bolted on deck with 12" steel plates enveloping the entire deck perimeter. That's it. These had no propulsion - they were towed into position by Casemate Ironclads or Sidewheel Steamers. They would then be anchored in shallow waters along the shoreline to commence bombardment.

As far as my casual research goes, these appear to have been the only boat of this type built by America, filling a very niche role in siege warfare by being purpose-built solely for littoral sieges of forts, seeing usage exclusively in the American Civil War. The most notable engagement of these AFAIK was on Feb 28 - April 8 of 1862 during the Battle of Island No. 10.

The mortars were so large (and percussion so great) that as seen pictured, upon firing crew had to actually exit the battery and fire via pullcord. After it fired, they'd squeeze through the plating's portholes to reload. These fired 13" diameter ball

You can see these were purpose built for destruction only. NOT safety. Just look at the minimal space sailors had on the outside of the plates lmao.. the balls on these guys.

Worth noting, a lot of men back then did not know how to swim!

My fav pic is probably #2. Cozy tents :)