More than 20,000 residents were forced to evacuate their homes on Wednesday in Germany after three World War II-era aerial bombs were discovered. The operation would take the bomb squad hours to complete their task.

The three bombs were found during exploratory work in the German city of Cologne on Monday, resulting in what officials called the largest evacuation of the city since the end of World War II, the Associated Press reported.

According to a news release by city officials, two American 20-hundredweight bombs and one American 10-hundredweight bomb with impact fuses needed to be defused.

This operation prompted the evacuation of 20,500 residents from their homes in order to prepare for the operation.

More than 20,000 residents needed to evacuate an area in Cologne, Germany, after three World War II bombs were found. (Thomas Banneyer/dpa via AP)

“The three World War II bombs in Deutz have been defused. At 7:19 p.m., the three unexploded bombs that had paralyzed large parts of the city were defused,” the post read. “The closed streets and bridges are now gradually being reopened, and residents can return to their homes or are being brought back by ambulance or shuttle buses.”

According to the National WWII Museum in New Orleans, Cologne was a frequent target for Allied air raids, with the first of 262 happening on a May 17, 1940, Royal Air Force bombing mission.

The defusing of the three World War II bombs took nearly 12 hours. (Thomas Banneyer/dpa via AP)

During that time, 770,000 residents evacuated the city, leaving about 20,000 behind.

The final bombardment was on March 2, 1945. American tanks entered the city a few days later.

Nick Butler is a reporter for Fox News Digital. Do you have any tips? Reach out to Nick.Butler@Fox.com.