Could Japan have used sea control or long-range submarines to disrupt American trade and industrial movement to the Pacific?
Short answerIt could have delayed U.S. deployment by attacking Pacific-coast and Panama-linked shipping, but American industrial depth would eventually build the forces needed to clear the routes.
NotesMuch U.S. industry lay nearer the Atlantic, while limited transcontinental rail capacity left substantial cargo to move through the Panama Canal and along the Pacific coast. Long-range Japanese submarines with reliable weapons could have delayed that flow and forced a costly response. Interdiction might extend the war, but American industry could build escort and combat forces on the Atlantic side, clear the routes, and resume the advance.