What is it?
My best guess is that this drawing shows an amphibious assault craft used by cattle during a general bovine uprising. It's like a medieval Higgins boat. It was notably unsuccessful because the submerged ram in the bow tended to cause the boat to run aground too far out from the beach, thus exposing the cattle to longbow fire while they swam to the beach. In short, this design failed because it tried to do too much.
Cows are yummy, but they're terrible at naval architecture.
-via Via Angus