Blockhouse
In military science, a blockhouse is a small fortification, usually consisting of one or more rooms which with loopholes, allowing its defenders to fire in various directions. It usually refers to an isolated fort in the form of a single building, serving as a defensive strong point against any enemy that does not possess siege equipment or, in modern times, artillery. A fortification intended to resist these weapons is more likely to qualify as a fortress or a redoubt, or in modern times, be an underground bunker. However, a blockhouse may also refer a room within a larger fortification, usually a battery or redoubt.