Leviathan

After his parents are assassinated, young Prince Alek Ferdinand runs away from his own government, the Austro-Hungarian Empire, which wants him dead. At the same time a young woman, Deryn Sharp, a commoner, disguises herself as a man to enter the Air Men of the British Army. With the aid of her brother she enters a flying airship made of a giant whale. Deryn and Alek travels cause them to cross paths many times before Alek discovers who Deryn really is.