David Crossland in Der Spiegel:
In the whole of Germany, more than 2,000 tons of American and British aerial bombs and all sorts of munitions ranging from German hand grenades and tank mines to Russian artillery shells are recovered each year. Barely a week goes by without a city street or motorway being cordoned off or even evacuated in Germany due to an unexploded bomb being discovered.
Nazi Germany was first to launch massive air raids on civilian targets in World War II with devastating attacks on Warsaw and London. But, it reaped what it sowed as the Allies waged a five-year campaign of aerial bombardment during which they dropped 1.9 million tons of bombs to destroy Germany’s industry and crush public morale. The raids killed an estimated 500,000 people.
Most estimates for the percentage of unexploded bombs range from 5 to 15 percent — or between 95,000 and 285,000 tons. As Germany hastily rebuilt its cities after the war, authorities didn’t have the time or the means to locate and dispose of a large part of that tonnage.
As a result, a deadly legacy has lain dormant beneath Germany’s streets ever since.