Most of us who stayed awake for American History have heard of the the Monitor.
Fewer of us are probably aware that the Monitor was the first of a very large build of
Monitors. Variants with 1, 2 and 3 turrets were built for the US Navy, and used extensively in the campaigns of the Civil War.
The most obscure point is that the ship type survived through WWII, the British ordered the
Roberts class monitors in 1940 and they served in the Mediterranean and Normandy, providing gunfire support for ground troops.