The bunker is a building in the Conquerors 3 with incredibly high health. It's official purpose is to garrison troops in case of a missile attack, but it is also used a distraction.
The bunker can be used to protect units from a missile attack, though if a player is watching for missiles, they can likely move the units out of the blast zone quicker than the time it would take to garrison them. Instead, the best use of a bunker is as a distraction building. By outlining one's base with bunkers, enemy units will focus fire on the bunkers, rather than more immediate threats like turrets. And because bunkers have such high health, enemy units will be focused on destroying the bunker for a long time, giving a player's defenses plenty of time to severely harm the invading force.