Early in 1958 a moratorium against further testing of nuclear explosions was under consideration, partly in reaction to international concern about the world-wide fallout of radioactivity from nuclear tests by the several nuclear nations. Before the moratorium, however, an intensive series of tests called Operation Hardtack was conducted. Operation Hardtack took place in 1958 both at Eniwetok Atoll as Phase I and at the Nevada Proving Grounds as Phase II, thereby breaking the pattern of alternate testing years at the sites. Between 5 May and 26 July 1958, twenty-two tests were conducted at Eniwetok under Operation Hardtack, Phase I. This one intense period of testing thereby constituted over half of the 43 total tests conducted at the Atoll over the entire ten years of testing. Following Operation Hardtack, the joint moratorium on testing by the U.S., and the U.S.S.R. started on 31 October * 1958. This marked the end of all nuclear tests at Eniwetok. The intervening 15 years until the present time have allowed some natural restoration of vegetation on affected islands and have provided the time for a tremendous decrease in the residual radioactivity resulting from the tests. Two islands were altered in this Operation Hardtack, Phase I. The test Koa was a surface explosion on the small island Bogeirik (Bokaidrik in Marshallese and Helen by the U.S. code name). island from the Atoll. This test removed the The other was Test Cactus at the northwest tip of Runit Island (Yvonne by the U.S. code name). This produced a crater nearby and to the Southwest of the La Crosse crater. s io