:To assure auxiliary propulsion of diesel submarines, DCN developed an anaerobic (atmosphere independant) system called MESMA. It is an electrical energy production using a turbo Generator supplied by a heating system in which the hot gases are produced by combustion of fuel (gasoil) and oxygen stored on board of the submarine. One injects in the combustion chamber to cool gases a part of condensates of these same gases. The medium concentrates itself in aggressive species, mainly sulphurous species coming from gasoil, and three types of corrosion risks must be taken into account : - Molten salt corrosion of the combustion chamber (salts in solution in the diesel oil and recirculated condensates and which become molten salts during the combustion and the evaporation in the flame), - high temperature oxidation and scaling in the hot parts, under the action of the combustion gases, - corrosion by the hot acidic condensates (until temperatures of the order of 250degreesC). Corrosion resistance in combustion gas condensates appeared to be the critical point. Subsequently.. a study was performed to search for the materials resistant to this type of corrosion, taking also into account the other materials features determining their possibility of use (resistance to the other types of aggression, high temperature characteristics, weldability...). Considering the gasoil used and the process, the representative conditions to perform tests were defined and the main tests consisted in exposure of samples with examination of surfaces and electrochemical tests at 250degreesC. They have been completed by tests at 80degreesC to verify that there was not inversion of material behaviour at intermediate temperatures. A large number of materials were tested : austenitic, duplex and ferritic stainless steels, nickel and cobalt alloys, unalloyed titanium and zirconium. The first tests, that mainly involved NiCr22Mo9Nb4 nickel alloy used by DCN in other applications, quickly highlighted selective corrosion of nickel, displayed by nickel enrichment corrosion products and resulting in localised corrosion taking the shape of pits or cracks. The risk of corrosion varies little with the concentration of sulphuric acid, but increases as the medium is made more oxidising. The nitric acid at these temperatures seems to behave in particular like an extremely powerful oxidant even at low concentrations. The following tests reinforced this result and showed that there is a direct relation between the corrosion resistance of an alloy in this medium and its concentration in nickel and in cobalt, except for the titanium that doesn't contain any of these two elements but is sensitive to pitting. The highest resistance alloys are those having high chromium content and limited nickel content, i.e. superferritic, duplex and austenitic stainless steels, as well as the zirconium. Electrochemical tests confirmed the good behaviour of stainless steels and zirconium, their steady passivation on a large domain of potential permitting to assure their corrosion resistance even though the electrochemical conditions vary somewhat. Besides, rotation of the working electrode permitted to simulate the circulation of the fluid on the surface of a tube at a speed of the order of 1 m/s. Dealing with the cost of materials, their availability and the easiness to work them, the best candidates are the 316 family austenitic stainless steels. 316Nb (X6CrNiMo17-12-3) and 316LN (X2CrNiMo17-12-3Az) alloys are preferable, due to their better mechanical characteristics at high temperature.