Unexploded ordnance (UXO or sometimes also abbreviated to UO), unexploded bombs (UXBs), or explosive remnants of war (ERW) are explosive weapons such as bombs, shells, grenades, land mines, naval mines and cluster munitions that did not explode when they were deployed. Unexploded ordnance still poses the risk of detonation, even decades after they were used or discarded.

Between 1940 and 1945, US and British forces dropped 2.7 million tons of bombs on Europe. Half of those bombs targeted Germany. Experts estimate that close to a quarter of a million bombs did not explode due to technical faults. Thousands of these bombs are still hidden underground, sometimes a few meters down and sometimes just below the surface.

The industrial Ruhr area and the Lower Rhine region were heavily bombed, as were the cities of Dresden, Hamburg and Hanover. So this is where most of the unexploded ordnance is found. Bombs are usually unearthed during construction work or are discovered during the examination of historical aerial images. Experts say it could still take decades to clear all of the remaining unexploded ordnance.

When confronted with the discovery of an UXO, UO or a UXB, bomb disposal experts have to decide whether to defuse it or to carry out a controlled explosion. Many have lost their lives on the job. German authorities are under pressure to remove unexploded ordnance from populated areas. Experts argue that the bombs are becoming more dangerous as time goes by due to material fatigue.

Eleven bomb technicians have been killed in Germany since 2000, including three who died in a single explosion while trying to defuse a 1,000-pound bomb on the site of a popular flea market in Göttingen in 2010.

A 1.8-ton bomb dropped by Britain’s Royal Air Force (RAF) was found in the city center of Augsburg on December 20, 2016. The find prompted a large-scale bomb disposal operation and consequently the evacuation of over 54,000 people on December 25. To date, this remains the biggest evacuation for the removal of World War II unexploded ordnance in Germany.

Authorities conducted another big bomb disposal operation in May 2017, with 50,000 residents in the northwestern city of Hanover forced to evacuate their homes. Thirteen unexploded ordnances from the 1940s were removed. Hanover was a frequent target of Allied bombing in the latter years of the war. On October 9, 1943, some 261,000 bombs were dropped on the city.