Leviathon Trilogy by Scott Westerfield

I recieved this trilogy for Christmas and finally decided to read it.  It is a refreshing story that follows a similar story to WWI.  Only difference is the world is divided in Clanker and Darwinist groups.  Clankers only use machinery while Darwinist's have found a way to genetically make new species to use as war machines.  The Leviathon is the name of the Darwinist airship that is a large whale that can fly and has flying bats that eat metal and drop it on ships like bombs to destroy their masts afterwich they send the Kraken, a huge sea animal to devour the Clanker ships.  The Clankes on the other hand use electricity and ignitors to destroy the helium filled Darwinist ships.

The story follows two young people.  One, a clanker born royal who is being hunted down to be killed so he can not take thrown and the other a young lady who is dressing up as a boy to join the Darwinist army so she can fly.  Their stories interlace with one another and they find themselves working together to help end the war.  The clanker does not know the Darwinist is a girl.