The engineering firm of Holmes & Narver, Inc., AEC Facilities Division, was engaged by the Division of Biology and Medicine, USAEC, Washington, D. C., to conduct an underground group-shelter study. Specifically, the shelter tested in Operation Plumbbob was to be refined and improved. In addition to the refinement study, working plans, specifications, bills of materials, and a three-dimensional model were developed to enable the Atomic Energy Commission to obtain without delay realistic local cost estimates for construction of shelters of this type. Thus, technical information and details relative to a tested protective structure for both emergency and peacetime applications are made available. Presented here is a group shelter of conceptual design and size for twofold use: (1) emergency shelter and (2) normal peacetime activities. The adaptability of the shelter to peacetime activities increases its attractiveness from an economic viewpoint. It also improves the emergency potential because the occupants will become familiar with the shelter and because a structure in regular use will have regular maintenance. Figures 1 through 3 are plan views of the shelter; Figs. 4 through 7 are photographs of the shelter model. Although this engineering study has been made to satisfy an Atomic Energy Commission responsibility, it is hoped that the results will be useful to other organizations and groups interested in protective structures.