A military installation is a facility used by the military for a variety of purposes, such as housing, training, and operations. The four words used to describe a military installation are POST, BASE, FORT, and SILO. A POST is a military station or camp, typically one that is smaller than a BASE. A BASE is a large military installation, usually with permanent buildings and facilities. A FORT is a fortified military structure, often with walls and towers. A SILO is an underground structure used to store missiles or other weapons. An armybase is a large military installation used by the army.