The Who in this is easy.
On one side in the battle for Tikrit is the official Iraqi Army, Shia militia which support the Army, senior Iranian commanders who appear to be directing the other two, and further north the Kurdish Peshmerga forces who are prepared to try and block or harry an Islamic State retreat up into Kirkuk province.
On the other side are perhaps 1,000 fanatical and well-armed IS fighters in heavily built up areas who have had time to prepare their defences.
Waiting in the wings is the US Air force which is bombing IS elsewhere but not in Tikrit.
For now US airstrike in support of Iranian led ground operations would be a little embarrassing for Washington D.C. and Tehran has announced that the Iranian presence in Tikrit is led by Gen. Qasem Soleimani, the commander of its elite Quds force.
Video – Iranian backed Shia Militia unit – www.youtube.com/watch?v=gsqXWOg2wbI#t=507
The What is also fairly straightforward, at least in theory.
The attackers aim to surround Tikrit by taking all the villages and small towns which encircle it. A week into the operation and they have had some success taking Albu Ajil in the soutb, Tal Ksaiba in the east, and pushing IS defenders to the western edges of al Dawr. Unless they are beaten back, they should be able to press in from the east and west, pushing deeper into the city centre until they have IS pinned against the banks of the river Tigris which runs just to the east of the city.
The Why is more complicated.
After last year’s collapse in the face of an IS assault the Iraqi military needs a major victory. It has chosen Tikrit, Saddam Hussein’s home town, as a symbolic place to fight, and as part of a strategy. The army could have contained Tikrit and carried on with its plans to retake Mosul this year. Instead it has opted to win back Tikrit, curb the ability of IS to move about, and, using its hoped for victory, to galvanize the military into being able to sustain the major assault which will be required to take Mosul which is Iraq’s second largest city. Victory there would also send a signal to any wavering Iraqi Sunnis that their future is within the Iraqi state, not the IS ‘caliphate’.
The Iranians are there because an Iraq partially controlled by IS is considered a threat to Iran and Iranian interests in Iraq, Syria, and Lebanon. The Kurds are just happy to kill as many IS fighters as they can as they consolidate what looks increasingly like ‘Kurdistan’.
The Americans are in a bind. An Iranian backed Iraqi military victory over IS strengthens Iran, but an IS victory in Iraq harms American interests in the Middle East. If push comes to shove the Americans would prefer to see the Iranians fight IS on the ground rather than Washington using even limited American combat troops.
The battle for Tikrit will be hard, possibly long. If the army, the militias and the Iranians win, the scene will be set for the battle of Mosul and that will be much harder and longer. How much of Mosul will remain standing is unknown.