A Nazi U-Boat Once Sunk a US Ship in Maine’s Casco Bay If you've ever been to Fort Williams in Cape Elizabeth or to Peaks Island, you've seen the remnants of gun batteries and lookout towers. These were used in WW1 and especially in WW2 to protect Portland Harbor. You may think that World War II was fought far away from Maine, so you may be surprised by how close those nasty Nazis really got. How Busy Was Portland Harbor in World War II? The harbor was a hotbed of activity! The South Portland shipyards built over 235 Liberty ships...