Operations Function is responsible for the direction and coordination of all incident tactical operations. This is the hands-on get dirty function of the ICS. Organization will develop as required as the incident grows. On a small incident, the Battalion Chief will be the IC, all of the command team functions, and Operations Chief. But as the incident grows, that one person may need to spread the control out accordingly in both the Command Team and in the Operations Section.
Operations has three organizational units, the Branch, the Division, and the Group. The Branch usually disects the incident in huge plots - sometimes in half or in thirds. Inside the Branch, Divisions exist to cut the geographic area into smaller portions. Inside those Divisions are the actual firefighters, strike teams, and what the ICS calls Resources.
Groups are the odd ones. Usually, Divisions define geographic areas and Groups define types of specialized functions such as Medical or Search and Rescue. There can be a Ventilation Group, Interior and Exterior Groups etc on a Structure Fire. Groups and Divisions are in the same level on ICS, but seperate the geographic definition and the "specialized" functions. All groups and divisions answer to the same Branch Director.