The Defense Department is replacing Gen. David McKiernan as the top U.S. commander in Afghanistan today; his replacement will be Lt. Gen. Stanley McChrystal, who ran special operations in Iraq under Gen. David Petraeus and saw successes in the 2007 troop surge.

So why is McKiernan out?

According to defense officials who spoke to The New York Times, it's because they saw McKiernan as runnng too conventional of a campaign in Afghanistan. McChrystal, with special ops and counterinsurgency/counterterrorism experience, comes from a less conventional branch of the military.

Afghanistan experts I talked to said that things just aren't going that well in Afghanistan and that the administration wanted to see some results. If the administration's new model for Afghanistan focuses more heavily on counterterrorism than counterinsurgency, as Obama's new comprehensive policy suggested, McChrystal's special ops experience seems to fit with that goal.

It's also possible that Gen. David Petraeus wanted someone who could bring experience with the Iraq troop surge directly to bear on Afghanistan. If the U.S. military wants to translate what it's learned in Iraq about fighting a guerilla war against muslim extremists, McChrystal's work in Iraq might be a more direct attempt to do that. McKiernan led the effort to topple Saddam Hussein in Iraq; McChrystal was an integral part of the phase the Obama administration now wants to emulate.

McKiernan, who already served as NATO commander in Afghanistan, took control of U.S. forces in 2008. Three different overarching command structures were involved in the Afghanistan effort, and as commander, McKiernan would have had to report to all three CENTCOM (Central Command), EUCOM (European Command), and SOCOM (Special Operations Command).

"[McKiernan] found this disjointed command structure very problematic," one expert told me. "He's a military guy, and he'll say, 'Well, we do the best with what we're given.'"

Observers have congratulated Petraeus on his ability to slice through military bureaucracy (though much of this has had to do with his ability to reach down into the chain of command to subordinates); it's possible Petraeus wanted someone who could better deal with a complicated command structure.

The transition to McChrystal could also have to do with the envisioned timeline for U.S. involvement there. McKiernan has historically asked for more troops to be sent to Afghanistan, and he indicated in February that the 17,000 additional U.S. troops recently sent to Afghanistan could stay there as long as five years; that's a long-term presence the Obama administration might want to avoid--or at least appear as if it's trying to avoid--especially as it begins to feel some pressure from Congress to keep U.S. involvement there as brief as possible.

Today's surprise move, at the very least, signals that the administration wants to take control of the situation in Afghanistan. Appointing someone with special ops background gives the appearance of a sleeker operation, more committed to the counterterrorism mission than to long, drawn-out conventional warfare, at least in the public eye. Whether this will change things in Afghanistan, or whether the effect will be limited to these cosmetics, has of course yet to be seen.

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