With the diving watch U1, Sinn engineers succeeded in developing a diving watch in which the quality of material and design gives it superior resistance to external influences under extreme conditions of use. In their search for a steel with the desired resistance, the Sinn engineers found what they were looking for at the German submarine manufacturer ThyssenKrupp Marine Systems: the steel manufacturers supply small quantities of the original steel of the current German submarine production exclusively to Sinn for making diving watches — the very steel of which the external hulls of the German Navy's new submarine class 212, which currently represents the most advanced non-nuclear submarines in the world, are made. This original submarine steel is not only extraordinarily seawater-resistant but is also of the highest non-magnetic quality without any residual magnetism.