The concrete ″Sea Tank″ , post-tensioned in three directions, has been developed by the Sea Tank Company of France. The design and subsequent model tests have produced a viable and practical facility, completely stable on the sea floor. It is capable of resisting and predicted horizontal and uplift forces without the use of piling or other anchorage, and can be constructed using techniques materials, and equipment readily available today. Comprehensive theoretical studies have been carried out using mathematical programs to establish the resistance of the structure to the various hydrodynamical forces acting against it. The studies and verifying model basin tests considered the forces acting on the structure in conjunction with the performance of the tank during towing, immersion, and operation. The spectrum of studies and tests covered a range varying from calm seas to the conditions imposed during the ″100 year storm″ in the North Sea.