at survival retreats, an architectural element that he calls a "crushroom". Both Bruce D. Clayton and Joel Skousen have written extensively on integrating fallout shelters into retreat homes, but they put less emphasis on ballistic protection and exterior perimeter security than Cooper and Rawles. Retreat logistics Anticipating long periods of time without commerce in the future, as well as observing documented history, retreat groups typically place a strong emphasis on logistics. They amass stockpiles of supplies for their own use, for charity, and for barter. Frequently cited key logistics for a retreat include long-term storage food, common caliber ammunition, medical supplies, tools, gardening seed, and fuel. In an article entitled "Ballistic Wampum" in Issue #6 of P.S. Letter (1979) Jeff Cooper wrote about stockpiling ammunition far in excess of his own needs, keeping the extra available to use for bartering. In their books, Joel Skousen, Mel Tappan, and Howard Ruff all emphasize the need to have a one-year supply of storage food. Mainstream economist and financial adviser Barton Biggs is a proponent of well-stocked retreats. In his 2008 book Wealth, War, and Wisdom, Biggs has a gloomy outlook for the economic future, and suggests that investors take survivalist measures. In the book, Biggs recommends that his readers should “assume the possibility of a breakdown of the civilized infrastructure.” He goes so far as to recommend setting up survival retreats: “Your safe haven must be self-sufficient and capable of growing some kind of food,” Mr. Biggs writes. “It should be well-stocked with seed, fertilizer, canned food, wine, medicine, clothes, etc. Think Swiss Family Robinson. Even in America and Europe there could be moments of riot and rebellion when law and order temporarily breaks down.” Survivalist retreats worldwide Survivalist retreats, both formal and informal exist worldwide, most visibly in Australia, Belgium, Canada, France, Germany (often organized under the guise of "adventuresport" clubs), New Zealand, Norway, Sweden, and the United States. Government operated retreats Construction of government-built retreats and underground shelters—roughly analogous to survivalist retreats—has been done extensively since the advent of the Cold War, especially of public nuclear fallout shelters in many nations. The United States government has created Continuity of Government (COG) shelters built by the Department of Defense and Federal Emergency Management Agency ("FEMA"). These include the massive shelter built under the Greenbrier hotel (aka Project Greek Island), military facilities such as Cheyenne Mountain Complex, and the Raven Rock Mountain