So, disregarding the simple fact that they can, we might ask why Iran is engaging in such a clear provocation? This is exactly the sort of incident at sea that many of us were worried would be ginned up in order to justify military action, and the Iranians just go and hand it to the Bush Administration?! Hasn't the Supreme Jurisprudent been paying attention? Don't they know we've got a crazy cowboy in charge who hasn't used his trigger finger in a few months? The silver lining of our concocted War in Iraq was supposed to be that people would be afraid of our crazy asses! We were supposed to get serious mileage out of the utter depravity of the justifications for the war, using our red-eyed frothing to make bad guys back down across the globe. Instead, they see right through us... our bluster and bravado starts sounding pretty hollow when they hear that the Joint Chiefs might resign rather than be party to an attack on Iran. Such are the wages of the Iraq War. We are no longer a super power because we cannot project force. We can no longer push around the little guys.
So, given that they are obviously ballsy (or shrewd) enough to call our bluff, why are the Iranians doing it? They could be moving to embarrass Tony Blair on his way out of office. It could be a rogue operation commenced without central authority. But I think the most likely explanation is something that's so en vogue in the Middle East: the hostage swap.
Remember the time we advanced the phony theory that Iran is behind the deaths of Americans in Iraq via EFPs? At around the same time, we captured a number of Iranians that we said were involved in these operations. We even stormed a consulate to do it. Ringing bells? Well, we've got Iranians, and for all intents and purposes, they've got Americans. Do you think they'll let theirs go without us playing along? Why? What's in it for them?
If I were the Iranians, I'd play hardball. Since they've already called our bluff, they should keep up the pressure. "Your soldiers are no longer on the coast. They are in Tehran. We will not let them go, under any circumstances, until you release our diplomats in Iraq. If you'd like to launch a rescue mission, then I refer you to President Bush's statment: Bring It On." As we've seen before, such a rescue mission could easily end in disaster, and no one will be willing to take that chance. We'd be forced to agree to their demands.
So, if you want to play along, watch the news for tales of released Iranians in Iraq.