The Pentagon and War Colleges war game hundreds of scenarios - some are gamed many times - so this is not unusual nor does it hint at any action by Israel or the US against Iran.
But the results of this top secret exercise - obviously leaked by opponents of an Israeli strike - is pretty bad news.
New York Times:
The two-week war game, called "Internal Look," played out a narrative in which the United States found it was pulled into the conflict after Iranian missiles struck a Navy warship in the Persian Gulf, killing about 200 Americans, according to officials with knowledge of the exercise. The United States then retaliated by launching its own strikes on Iranian nuclear facilities.
The initial Israeli attack was assessed to have set back the Iranian nuclear program by roughly a year, and the subsequent American strikes did not slow the Iranian nuclear program by more than an additional two years. However, other Pentagon planners have said that America's arsenal of long-range bombers, refueling aircraft and precision missiles could do far more damage to the Iranian nuclear program - if President Obama were to decide on a full-scale retaliation.
The exercise was designed specifically to test internal military communications and coordination among battle staffs in the Pentagon, Tampa, where the headquarters of the Central Command is located, and in the Persian Gulf in the aftermath of an Israeli strike. But the exercise was written to assess a pressing, potential, real-world situation.
In the end, the war game reinforced to military officials the unpredictable and uncontrollable nature of a strike by Israel, and a counterstrike by Iran, the officials said.
No doubt this particular scenario will be war gamed several times. But it is safe to say that there will be no outcome that would be perfect for either the US or Israel. Iran will retaliate against Israel and blame the US anyway - even if we don't participate in the original attack. What flows from that will not necessarily be worse than a regional war, but there will be little to celebrate.