In the original TMP Marshal Savage proposed the use of submarine habitats as a training ground for prospective space residents who would use life in such habitats as a means of growing familiar with living in confined spacecraft-like spaces and coping with the demands of maintaining an artificial life support system. NASA and other government space agencies have employed submarine habitats with similar objectives. There is no question that the marine environment offers a closest analogy to the microgravity environment and that underwater facilities will be a practical tool in space development. But the need for large communities underwater is unlikely. However, this will not deter the demand for underwater habitat structures of some kind for Aquarius, even if their function is less practic