6-36. A defensive situation may require the headquarters staff to plan for retrograde tasks in combination, sequentially, or subsequent to the defensive mission. Planning and rehearsing a rearward passage of lines of security forces forward of the MBA is critical to ensuring proper execution while under enemy pressure. The complexity and fluidity of retrograde operations and the need to synchronize the entire operation dictate the need for detailed, centralized planning and coordination with decentralized execution. A retrograde may be forced or voluntary. In either event, a higher echelon commander must approve it.