 Halo 3 was initially conceived before Halo 2 was released in 2004 . Much of the staff were preoccupied in making extra content for Halo 2 , while others continued with the groundwork for the development of Halo 3 . Bungie remained quiet as to what their new project was , leaving comments in their weekly update alluding to a " new project " . The game was officially announced with a real @-@ time cinematic trailer at E3 2006 . 
