William Arkin, who served as the US Army's top intelligence mind on West Berlin in the 1970s and accurately predicted US military operations against Iraq, said the plan is known in military circles as TIRANNT, an acronym for "Theater Iran Near Term."

It includes a scenario for a land invasion of the country led by the US Marine Corps, a detailed analysis of the Iranian missile force and a global strike plan against any Iranian weapons of mass destruction, Arkin wrote in The Washington Post.

US and British planners have already conducted a Caspian Sea war game as part of these preparations, the scholar said.

"According to military sources close to the planning process, this task was given to Army General John Abizaid, now commander of CENTCOM, in 2002," Arkin wrote, referring to the Florida-based US Central Command.

But preparations under TIRANNT began in earnest in May 2003, when modelers and intelligence specialists pulled together the data needed for theater-level warfare analysis for Iran, he said.

This effort has never stopped. The plan has since been updated using information collected in Iraq, the analyst pointed out.

Air Force planners have modeled attacks against existing Iranian air defenses and targets, while Navy planners have evaluated coastal defenses and drawn up scenarios for keeping control of the Strait of Hormuz, the gateway to the oil-rich Gulf.

A follow-on TIRANNT analysis, which began in October 2003, calculated the results of different scenarios for action against Iran to provide options to US commanders, Arkin wrote.

The Marines, meanwhile, have come up with their own document called "Concept of Operations" that explores the possibility of moving forces from ship to shore against a determined enemy without establishing a beachhead first.

"Though the Marine Corps enemy is described only as a deeply religious revolutionary country named Karona, it is -- with its Revolutionary Guards, WMD and oil wealth -- unmistakably meant to be Iran," Arkin said.

Various scenarios involving Iran's missile force have also been examined in another study, initiated in 2004 and known as BMD-I, which is short for "ballistic missile defense -- Iran", Arkin said.

In June 2004, US Defense Secretary Donald Rumsfeld alerted the US Strategic Command in Omaha, Nebraska, to be prepared to implement CONPLAN 8022, a global strike plan that includes Iran.

"The new task force, sources have told me, mostly worries that if it were called upon to deliver 'prompt' global strikes against certain targets in Iran under some emergency circumstances, the president might have to be told that the only option is a nuclear one," Arkin said.

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