Nice articulated bus, Judah!
Hi, this is an american mortar for coast fortifications for sounds, inlets, closed bays and other confined waters.
In an era when the deck armour was weak, a plungging shot was very dangerous for the attacking ship. The mortars were grouped in batteries of 4, and the concentred fire of 2 or 4 batteries, even with the primitive FCS of the late XIX century, the risk of impact for an attaking vessel was high. The recoil system was under the floor, and also the entire battery was under ground level, so it was invisible from the sea.