During the Cold War, most of Pennsylvania was considered expendable.
Anti-aircraft missiles encircled the nation's largest cities to as a final line of defense against Soviet bombers. Pittsburgh was chosen because of its industrial value and Philadelphia was picked in part because of its Navy shipyard. Both were also strategic areas with regard to the nation's capital.
Hundreds of servicemen worked at these sites, and the government encouraged public outreach and events to help residents feel at ease with the missiles in their backyards.
Decades later, these sites remain a part of their respective communities, though their roles have changed. Instead of the servicemen contributing to society, it is the buildings and land left behind.
But these former missile sites leave few clues to their unique history.