The U.S. Central Command (CENTCOM) has been conducting theater campaign analysis for a full scale war with Iran since at least May 2003, responding to Pentagon directions to prepare for potential operations in the "near term."
The campaign analysis, called TIRANNT, for "theater Iran near term," posits an Iraq-like maneuver war between U.S. and Iranian ground forces and incorporates lessons learned from Operation Iraqi Freedom.
In addition to the TIRANNT effort and the Marine Corps Karona invasion scenario I discussed yesterday, the military has also completed an analysis of Iran's missile force (the "BMD-I" study), the Defense Intelligence Agency has updated "threat data" for Iranian forces, and Air Force planners have modeled attacks against "real world" Iranian air defenses and targets to establish new metrics. What is more, the United States and Britain have been conducting war games and contingency planning under a Caspian Sea scenario that could also pave the way for northern operations against Iran.
After new reports of intensified planning for Iran began to circulate over the weekend, the President dismissed the news as "wild speculation."
http://blogs.washingtonpost.com/earlywarning/2006/04/despite_denials.html#more