Abstract: A method for laying underwater pipelines in deep water, using the J launching technique, comprising joining together mixed-structure pipes consisting of a steel core reinforced with a composite material consisting of a hardenable material containing continuous fibers and in which:the continuous fiber is wound about the steel core as a helical winding which forms an angle of between 65.degree. and 87.degree. with the pipe axis;the ratio of the thickness of the composite layer to the thickness of the steel core is between 2 and 8;the weight of the mixed-structure pipe in water is between about 40 and 100 kg/m.