: troops under threat of atomic attack. A miniature mortar drives a propelling charge into the earth, where an excavating charge blasts out the foxhole. The entire device weighs less than 5 Ib, and the cost is estimated at Jess than $10. For civil defense purposes somewhat larger devices based on this principle could be stored in advance of attack in neighborhoods and communities. On receipt of a yellow or strategic alert these devices could be distributed quickly and the householder could excavate a family shelter, roof it with doors, etc., and spread the excavated earth over the improvised roof. This type of improvised shelter should provide nearly perfect protection from primary thermal and secondary blast effects. The extent to which it attenuated radiation would be determined by the amount of earth cover, but could be close to unity. For cities where evacuation may be feasible (such as Dayton in this study) such a device could provide a means for providing fallout cover in the reception areas. The cost of enough devices to shield the entire us population would be of the order of $700 million. TIME REQUIRED AND AVAILABILITY OF MATERIAL Mass evacuation plans could perhaps be developed in 6 months, but as yet no city has completed satisfactory plans, and many have been working on them for up to 3 yr. An additional 12 months would probably be required to implement and practice acity’s plan to the point at which it could be considered adequate. To construct shelters for a large-scale shelter program would require at least 12 months — up to 24 monthsif land had to be acquired through condemnation procedures. The Cincinnati Milling Machine Co. shelters, however, were completed in 7 months. There is no shortage of concrete or reinforcing steel (the major materials used in shelter construction), but the shelter program and the proposed road programs mightfind themselves in competition for these materials. IMPLEMENTING THE SHELTER PROGRAM It is true that each community will have varying shelter needs, but some general principles can be stated: (a) The first shelters should be constructed outside the congested urban core but within walking distance. This distance will vary. For coastal cities this might be within a walking time of ¥ hr. Inland cities may be able to disperse their shelters even more. (b) Planning must ultimately look forward to having a shelter entrance within a t0-min walking distance of each inhabitant. (c) The shelter program must be accompanied by a program of reduction in urban vulnerability through dispersal. Shelters built to conform to present population distribu- tions would still result in very large numbers of people being in the crater or lip in a daytime attack. Problems of implementation are treated in detail in Annex B of this appendix. 66 ORO-R-17 (App B) CONFIDENTIAL