The latest expansion of the U.S. mission in Iraq centers on bringing Sunni tribes into the fight, a critical goal in the campaign to defeat the Islamic State group.

Up to 450 more U.S. troops will deploy to al-Taqaddum Air Base in Anbar Province to set up a new base to advise and assist Iraqi forces. There are two main goals: improve Iraqi military planning and tactics, and encourage inclusion of Sunni fighters.

This is how U.S. officials and the Pentagon say it will work:

— The new U.S. forces will begin arriving in six to eight weeks. About a quarter of them will be advisers; the remainder will provide security and other logistics.

— The U.S. forces will advise the 8th Iraqi Army Division, based at al-Taqaddum, on intelligence gathering, logistics, troop deployments and other tactical and administrative improvements to help them develop a plan to retake of Ramadi. That division includes forces that fled the Islamic State attack on the city last month.

— The U.S. will help forge connections between Iraqi security forces and Sunni tribes, assisting them in identifying and reaching out to Sunnis in Anbar so they can eventually work with the Iraqi Army.

— U.S. forces will not do combat operations, but may leave the base when needed to connect with Sunni tribes.

— The U.S. will provide armor, communications equipment and small arms, such as machine guns, to the Iraqi division.

— U.S. officials will expedite other weapons and supplies to the Iraqis.

— The immediate goal is to retake Ramadi, then move to secure the Euphrates River corridor and eventually retake Mosul.