 It also allows players to field units that are not available in normal Warhammer 40,000 games, such as large super-heavy tanks and robot-like titans, some of which can stand up to 400 feet in game-scale height.The first print of the Apocalypse sourcebook was released in October 2007, during the latter days of Warhammer 40,000's fourth edition.The release of the fifth edition of Warhammer 40,000 in 2008 prompted Games Workshop to start working on an update to the Apocalypse ruleset in order to streamline its compatibility with the new edition.