The Silithus Field Duty quest collection was added in patch 1.9 to the Silithus area. They were designed to provide casual players with the ability to achieve raid-level rewards, and require the character be a minimum of level 60. The Silithus Field Duty quest chain is only available after your realm completes the Gates of Ahn'Qiraj opening event and the outdoor war across Kalimdor officially ends (there is a server-wide announcement saying the qiraji armies are retreating).