A description is given of the German underwater simulator 'Gusi' which contributes to the development of high-tech products by permitting them to be tested in near-practice conditions as well as establishing quality references in reproducible conditions. The simulator is of two-storey design. On the ground floor are located the large horizontal working chamber and the vertical working chamber. Installed on the upper accommodation area are a living chamber with integrated prechamber and a medical treatment chamber with separated prechamber. Both chambers are connected via the transfer chamber. A diving bell is docked on top of the transfer chamber and can be transferred to the docking flange of the large working chamber. In the 'Gusi' diving system, manned dives can be performed down to 600 m depth of water and unmanned tests of components down to 1000 m or 2200 m respectively. A brief description is given of RRD program which focus on procedures and tools for welding and cutting under water, for non-destructive testing, cleaning and conserving.