How might the United States answer an 18-inch Agincourt?

If Britain built an 18-inch-gun HMS Agincourt, what might the American response have been?

The United States might have modernized its planned South Dakota concept into a faster, canal-constrained ship carrying twelve 16-inch guns.

The proposed American reply develops a design already under consideration: the planned 1920 South Dakota class. It keeps twelve 16-inch guns, whose combined broadside could compare well with eight British 18-inch weapons. A narrower beam and shallower draft preserve Panama Canal access, while turbo-electric propulsion supports a 25-knot target for facing a fast British capital ship. The result is a reasoned alternate-history reconstruction and was never a historical US Navy project.