Based on the Steampunk book series by Scott Westerfeld.
The fake movie trailer! [link]
Leviathan concerns the adventures of Prince Aleksander, on the run after his parents, the Archduke Franz Ferdinand and Princess Sophie Chotek, are murdered to advance the first world war. Only in Aleksander's world things play out a little differently. Each nation of Europe in this alternate timeline subscribes to either being a 'Clanker' or principally uses machines, or a 'Darwinist' who principally use genetically engineered animals for warfare and society. Aleksander is a Clanker and sets off into exile on board a Stormwalker mech.
Meanwhile Deryn Sharp has joined the British Airforce in the disguise of a boy. The living airship she travels in is called The Leviathan.
Both Clanker and Darwinist will meet by strange paths in the midst of a brewing war of mind blowing proportions between robots the size of mountains and beasts of war with cities on their backs.