The work reported here is innovative in that it presents a new design chart for circular cylinders collapsing under external hydrostatic pressure based on both theoretical and experimental data. The design chart consists of two straight lines, rather than the more complex curves typical of well-known codes. The design chart also allows the designer to design much shorter and thicker vessels than the standard codes do. The authors contend that this will enable engineers to design pressure vessels that can dive to a much greater depth than previously known. Currently, most large submarines can only dive to a maximum depth of about 400 m (0.25 mi.), but the maximum depth of the oceans is some 29 times deeper than this.