The Bunker protects soldiers by depositing them out of combat for up to 12 hours; higher level and a duty officer let you deposit more. Critically, the deposit function is NOT available during upgrade. Buildable at Keep 9. Duty Officer unlocks at Lv20 (increases Bunker Protecting Capacity; ideal Caterina Sforza or Clovis I). Maximum Protection Capacity by level+officer: base 100,000 at Lv20 to 400,000 at Lv40; officers add Junior +25,000, Medium +50,000, Senior +75,000, Special +100,000, Super +400,000 -- stated max 800,000 (Lv40 + Super officer). Keep-gated 1:1, cost F/L/S/O, speed +50% at Lv8 to +610% at Lv50, Power 10 (Lv1) to 157,000,000 (Lv50) -- a large late-game Power contributor. For a PvP/defense bot, the Bunker is the ghosting/troop-protection building; deposits must be timed around the fact that the deposit menu is disabled whenever the Bunker itself is being upgraded. Not an economy building, but its Power contribution makes it a base_dev consideration.
Original research source: Evony Guide Wiki