1. Apparatus with a changeable operating mode for detection and classification of a submerged moving object from a passive signal generated by the object and an active signal reflected from the object, the apparatus comprising: an active mode branch having an input for receiving a first signal representative of the active signal; a passive mode branch having an input for receiving a second signal representative of the passive signal, wherein the active mode branch includes first signal processing means adapted to generate a first classification estimate output with first clues of the most probable class of target for the object, and the passive mode branch includes second signal processing means adapted to generate a second classification estimate output with first clues of the most probable class of target for the object; a merger adapted to receive and merge said first and second classification estimate outputs, and to output a merged classification estimate output with clues; a classifier arranged to receive said merged classification estimate output with clues, and adapted to classify the object by performing classification based on said merged classification estimate output with clues; and a controller adapted to change the operating mode of the apparatus based on a result of the classification by said classifier.