The Greater Portland area, which includes the surrounding islands in Casco Bay, is home to many formerly used military forts. More prominent forts during the World War I era were Fort Williams in Cape Elizabeth, Fort Preble in South Portland, Fort Levett on Cushings Island, and Fort Mckinley on Great Diamond Island. During World War I these forts were either partially or fully manned in preparation for potential air raid attacks from Europe.

Pictured here is a boat in Casco Bay transporting soldiers between the islands and the mainland.