With an estimated amount of about 1.6 metric million tons, unexploded ordnances (UXO) in the German North and Baltic Sea pose a serious threat to the environment due to increasing corrosion. One way to allow safe salvage of the objects from the sea is to weaken them and then disarm them by low order detonation. This paper deals with the weakening by laser ablation, aiming for the introduction of ablation gaps with a depth of 2/3 the material thickness in 4 and 10 mm thick mild steel samples. An Yb:YAG laser source is used with a laser power of up to 2 kW in combination with a coaxial gas jet supplying the process zone with nitrogen to ensure a controllability of the process and the depth of the gap. The study is thus focused on achieving constant and predictable gap depths.