According to Wolfgang Spyra, a bomb researcher at the Technical University of Cottbus, the bombs had a dud rate of between 7 percent and 15 percent. Taking that information and deducting what has already been removed in Oranienburg, his team estimates that there are still at least 325 bombs underneath the town. ...When they were dropped 65 years ago, many bombs didn't explode due to Oranienburg's soft soil, which has a hard layer of gravel underneath. Bombs would often penetrate the earth, bounce off the gravel and come to rest underground with their tips pointing back upwards.