 Leviathan by Scott Westerfeld. In this alternate version of World War I, the German powers or clankers used mechanized war machines for their battles. The British powers, called Darwinists, used genetically fabricated living creatures for their war machines. Alexander is the son of Archduke Ferdinand, and he is a clanker. Darren is a Scottish girl who's pretending to be a boy so she can serve aboard an airship for the British Air Service. When they accidentally meet, will it be war or will it be rescue? Leviathan by Scott Westerfeld.