. . . . from the late-1950s to the mid-1980s one of the practices of the offshore petroleum industry was to put subsea assemblies in dry, one-atmosphere, water tight chambers right on the seafloor. This permitted oil field workers to be sent down to the seafloor in deep water diving bells or small submarines, and to enter the chambers to perform work in a “shirt sleeve” environment down on the seafloor itself. In the mid-1980s, the petroleum industry abandoned this practice, but this sort of capability has obvious implications for construction of non-commercial or clandestine sub-seafloor installations that have openings to the seafloor. Clearly, chambers of this sort can serve as transfer points for personnel, equipment and supplies to sub-seafloor facilities or bases of the sort discussed later in this book. Interestingly, Lockheed, the well-known aerospace company, developed one of these dry, seafloor, one-atmosphere systems for use in water of 1,200 feet depth, with studies showing that the technology could be extended to depths of 3,000 feet. . . .