1. A group of vessels having an unmanned surface vessel and an unmanned underwater vessel, wherein the underwater vessel comprises a sonar device, for sensing location data in the underwater area and one or more evaluation units, the evaluation units arranged in such a manner so as to include a detection device for detecting a contact (MILEC) by the sensed location data, and a classification device for classifying the detected contact (MILEC) as a mine-like contact (MILCO) or a non-mine-like contact (NONMILCO), wherein the classification is accomplished by comparing the contact (MILEC) with known mine information so that a mine-like contact (MILCO) can be identified as a mine contact (MINE) or as another object (NOMBO).