How quickly could America develop an 18-inch gun?

How long would the United States need to move from its existing heavy guns to an 18-inch naval weapon?

Roughly three to four years, because American 14-inch guns were already in service and 16-inch work had begun.

Gun development followed an industrial progression from American 14-inch weapons and early work toward 16 inches. That experience shortened the path to an 18-inch gun and its mountings without removing the development work. A rival British leap could therefore provoke an American answer within a few construction cycles. The Maximus design would not remain strategically isolated for long.