When does Leviathan return?

Leviathan is a 2009 novel written by Scott Westerfeld and illustrated by Keith Thompson. It is the first work in the trilogy of the same name, followed by sequels Behemoth and Goliath. The novel is set in an alternative version of World War I in which the Central Powers (known in-universe as "Clankers) use mechanized war machines and the Triple Entente (referred in text as "Darwinists") fabricate living creatures genetically for use in battle.