 The fortifications were defended by 25,000 Union Army soldiers and 45,000 local militia volunteers.Further defensive support of more than 15,000 men was provided by the so-called "Squirrel Hunters"--untrained volunteers from other parts of Ohio who carried outdated equipment.Construction of the defenses was directed by Colonel Charles Whittlesey until relieved by Major James H. Simpson, chief of Topographical Engineers for the Department of the Ohio.