The purpose of the project SARGOS is to develop a global alert and graded response system to answer the recent but strong need for securing critical civilian offshore infrastructures, vulnerable to piracy or terrorist actions from the sea. The challenge of protecting these infrastructures against malevolent intrusions requires to develop innovative strategies so as to ensure in a coordinate way the whole processing line: automatic surveillance, robust detection, continuous adjustment of the reaction plan and graded implementation of the relevant set of reactions. The system handles : Automatic and robust detection and classification of small size maritime targets in rough sea; Detection of suspicious behaviors in a security zone around the platform; Formalization and modeling of graded internal and external reactions, adapted to the dangerousness of the detected intrusion and taking into account security rules in force on the platform, geopolitical environment and legal aspects; Activation of progressive and reversible reactions, according to an intelligent situation analysis process. Reactions can go from a simple alert up to bringing non lethal reaction means into play. The project will materialize with the implementation of all the processing line in a single platform that will be used to carry out experimentations and to validate the overcoming of critical issues and the appropriateness of the proposed concept with regards to users' needs. SARGOS has been selected by the French National