The Lost Continent by Edgar Rice Burroughs
The year is 2137, over 160 years ago the "Great War" was fought in Europe. The Western Hemisphere stayed out of the conflict, as much as possible, using the slogan: "The East for the East ... The West for the West". For all this time the USA did not go past 30 degrees or 175 degrees latitude. Until.......
The aero-submarine, "Coldwater" in command of Lieutenant Jefferson Turck is blown past the 30 in a raging storm. Damaged, the ship landed in Europe only to find that it was not the enemy that was expected but something entirely different.
Originally published in 1915 as "Beyond 30".