The topic of munition in the sea and the associated dangers are becoming increasingly prominent due to ongoing corrosion and the corresponding release of toxic substances into the marine environment. In order to provide a safe defusing method for their salvage, the shell material needs to be partially weakened to about 1/3 of the material thickness. In this paper a dual nozzle system is utilized for optimized melt extraction, employing a Yb:YAG laser at a laser power of 2 kW on 10 mm thick mild steel samples under water. The process is investigated applying design of experiments methods regarding the depth of the notch and in particular the influence of the cutting gases oxygen, nitrogen and air. The impact of the weakening on the mechanical strength of the samples is determined by tensile tests.