'Adv Dispatch' is a Military-category research item at the Academy, NOT an auto-gather/auto-dispatch feature — per this source, leveling it up grants +1 march slot per level. It gates progress: you cannot upgrade the Keep to level 14 until 'Adv Dispatch Level 1' is researched (shown in red on the Keep upgrade screen if missing). Requirements to start researching Adv Dispatch: Academy Level 13, 900,000 Gold, and these prerequisite research levels already completed: Conscription Lv2, Swordplay Lv2, Infantry Armor Lv2, Feathered Arrow Lv2, Archer Armor Lv2, Formation Lv1, Horseback Riding Lv3, Cavalry Armor Lv3, Battering Ram Lv3, Siege Machine Armor Lv3, Tracing Lv3, Ground/Mounted/Ranged/Siege Troop HP Lv4 each, and Coordination Lv4. (Note: total march slots — including Adv Dispatch's contribution — are also capped/interact with VIP level; see 'How to get more March Slot' for the full +4 research / +1 VIP breakdown.)
Original research source: Evony Guide Wiki