The paper describes the design and analysis of underwater housings made of ultra-high performance concrete (UHPC) within the Helmholtz Alliance "ROBEX" to provide cost-efficient alternatives to expensive titanium housings. The research is related to former investigations on spherical and cylindrical shells under hydrostatic pressure made of normal strength concrete, performed from 1960 to 1980 at the Civil Engineering Laboratory, Port Hueneme, California. Several housings made of UHPC have been manufactured and the short-term implosion resistance has been determined experimentally. Since neither the mechanical equations for thin-or thick-walled shells nor the empirical equations for implosion pressure of shells made of normal strength concrete by Albertsen can describe the behavior sufficiently, two nonlinear material laws for concrete, multiPlas Law 9 (modified Willam-Warnke model) and Law 14 (Menetrey-Willam model) by Dynardo for ANSYS, have been calibrated with results from uni-and biaxial strength tests, and the results of nonlinear finite element model with ANSYS 16 have been compared. To study the long-term behavior, an in situ test is currently being performed at 2,500-m depth in the Arctic Sea.