The Land that Time Forgot by Edgar Rice Burroughs. In 1916 the US Montrose is fired on and sunken by a German U-boat. However the survivors manage to sneak aboard and capture the U-boat. In between subsequent coups, the British and Germans agree to an uneasy truce until they can reach a neutral port. But they become lost and instead arrive on the mythical continent of Caprona where dinosaurs and cavemen still roam.