The Beginning of Surge Combat?

It looks like both coalition forces and the insurgents might be changing tactics in Baghdad, as a signifigant combat operation in Baghdad enters a fourth day:

Hundreds of U.S. and Iraqi troops battled with insurgents in a stronghold of the Sunni insurgency in central Baghdad Tuesday.

The firefight began before dawn and followed two days of violence in the neighborhood that left as many as 50 insurgents dead.

The U.S. and Iraqi troops came under attack by snipers, mortar rounds, and small arms fire.

By midday Tuesday (4 a.m. ET), the U.S. military sent in fixed-wing aircraft and Apache attack helicopters to support the ground forces.

U.S. military sources said the insurgent group included elements from the Saddam Hussein regime, foreign fighters, and members of al Qaeda in Iraq.

They said the group was waging a sophisticated, coordinated battle, and was fighting against 400 U.S. troops and 500 Iraqi soldiers.

Combat started Saturday when Iraqi troops came under fire when trying to recover bodies dumped near a cemetery.

At this stage of the war it is rare for Sunni insurgents to engage in a multi-day battle against coalition forces, for obvious reasons: they have lost every single major engagement they have ever engaged in since the 2003 invasion, usually suffering heavy losses. They simply lack the training, support, weaponry or numbers to prevail in such conflicts, and so it is of note that they seem to have chosen to make a stand, of sorts, in this Baghdad neighborhood at this time. Why? What are they protecting, and what are they trying to prove? Why have they not slipped away under the guise of civilians as they so often do?

There is some sort of prize involved here, be it material, personnel, or philosophical. I'll be watching this story with great interest, and will provide updates as I can. This particular battle bears watching as a portent of what "surge" operations in Baghdad may look like in months to come.