Halo 3
The first work was started on Halo 3 before the release of Halo 2 in 2004. Through 2004/2005 Bungie refused to confirm they were working on Halo 3, only saying that they had a 'new project'. The game was officially announced with a trailer at E3 2006. While details of the multiplayer were openly announced and talked about before release, details of the story were kept mostly secret until the day of the launch.