Underwater activities, such as surveying or interventions, carried out by autonomous robots, can benefit greatly from using a vision system. Optics based systems provide information at a spatial and temporal resolution higher than their acoustic counterparts. At present, they are the best option when high precision maneuvering and manipulation is needed, if there is good visibility. This paper presents a new system designed to provide visual information in submarine tasks such as navigation, surveying, mapping and intervention. The main advantages of our system, called Fugu-f (Fugu flexible), are its robustness in both the mechanical structure and the software components, its flexibility, since it is installed as an external module and is adaptable to different vehicles and missions, and its capacity to operate in real-time. Experiments of surveying and object manipulation carried out in real conditions in the context of the TRIDENT project show the suitability of the system and its scientific and industrial potential applications.