6-142. Defending corps and divisions fight the decisive battle in accordance with their commander’s concept of operations. That battle occurs either at the FEBA or within the MBA. Commanders position forces in the MBA to control or to repel enemy penetrations. The division commander assigns each BCT an AO within the MBA on the basis of the defending BCT’s capability, the terrain within that AO, and the mission. Assigned BCT AOs usually coincide with a major regimental- or brigade-size avenues of approach. Commanders should not split responsibilities for avenues of approach. The force responsible for the most dangerous AO in the MBA normally receives priority in the initial allocation of artillery, engineer, EW, and CAS capabilities. It is the initial main effort.