Leviathan by Scott Westerfeld:
As much as I love airships, the Leviathan in Scott Westerfeld's novel still creeps me out a bit. It is not a machine but a giant, genetically engineered whale fabricated by the British Darwinists to fly in the sky supported by enormous biologically generated hydrogen-filled bladders. The Leviathan is more than a single "beast." It is actually a whole ecosystem of creatures, and her purpose is to fight the Central Powers composed of the Austro-Hungarians and Germans and their "Clanker" diesel-fueled armies. Employing an odd assortment of genetically altered birds, bats, and other creatures, the novel creates unforgettable combat scenes between Darwinist and Clanker forces featuring both air-to-ground and air-to-air clashes.
The protagonist is Deryn, a commoner girl who disguises herself as the boy (Dylan Sharp) to take a position in the British Air Service. Through a series of exciting events, she gains a spot aboard the Leviathan as a rigger, and after a crash landing in Switzerland, meets Prince Aleksander. He is on the run from agents of his own government that seek his demise. The two join forces and even combine the technology of Clanker and Darwinist to repair (and improve) the damaged Leviathan.
Set in the era of WWI and replete with powerful, heavily armed diesel-powered machines, this novel might be more accurately classified as Dieselpunk rather than Steampunk. However, it is just old enough and contains enough of the Edwardian era to maintain the Steampunk genre. Regardless of its classification, Leviathan blends so many different elements that it hard to pin down in any case. It is truly a wild ride of imagination, intrigue, action, and adventure. The books in the sequel continue to follow the crew of the Leviathan as they circumnavigate both the geographical and political world and discover new and terrifying genetically altered beasts engaged in a global conflict.
Get the Whole Series
Book 1 - Leviathan
Book 2 - Behemoth
Book 3 - Goliath