Advanced Redoubt defended the Pensacola Navy Yard with layered obstacles meant to wear down attackers before they could reach it, including long-range cannon fire, short-range infantry fire from the outer wall, and crossfire between the outer and inner walls. If attacking soldiers reached the ditch, riflemen firing through narrow protective loopholes and cannoneers firing canister from howitzers in the gun chambers would trap them in a deadly crossfire. The fort was considered vulnerable chiefly to siege, but despite its innovative design, it represented the end of an era in coastal fortifications. Begun in 1845 with enslaved workers and completed in 1870 by free citizens, its cement-filled masonry walls marked a transition toward reinforced concrete batteries that could resist rifled cannon more effectively than brick.