Nearly half the residents of the German city of Koblenz are being forced to leave their homes this weekend after the discovery of a 2-ton, unexploded World War II bomb, marking the biggest bomb-related evacuation in Germany's post-war history.

Some 45,000 residents of the Rhineland city—including those in a jail, two hospitals and several nursing homes and hotels—are under orders to evacuate by Sunday, when a bomb-disposal squad plans to defuse the 10-foot bomb dropped by British fliers, most likely in a 1944 bombing raid....