Template:Ratings Considered by Halo Wars's Lead Designer, Graeme Devine, the Circle Menu is probably the most important menu in the game. It is so large that the menu itself takes up the whole screen. It is used, to quote the L.D, "... for everything. To building infantry, to building vehicles, to building buildings and for calling in "Leader Powers". The player can navigate through the Circle Menu via the Analog stick, to select whatever they so choose.
Sources
http://forums.halowars.com/forums/1/91352/ShowThread.aspx#91352