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.

To ensure reliably that the rotating bezel of the diving watch does not detach under harsh impacts, it is attached as a captive bezel to the central part of the case.

The water-resistance and pressure resistance of 100 bar (= 1000 m water depth) was certified for the diving watch U1 by DNV. The safety test pressure used for this purpose was 125 bar.