helicopters to complete some of the work begun during Highjump. The International Geophysical Year and the Antarctic Treaty In 1956–57 the U.S. Navy, during Operation Deep Freeze I, and in conjunction with research teams funded by the National Science Foundation, established seven research stations in Antarctica to prepare for the International Geophysical Year (IGY, 1957–58). The IGY was an intensive, multi-national, multi-disciplinary, global research effort designed to study a wide range of geophysical processes. Much of that effort took place in Antarctica and was crucial in establishing Antarctica as a continent for peace and science. The international coordination that resulted from the IGY ultimately lead to the Antarctic Treaty, which was signed in 1959. Since then, Treaty nations have agreed to several addenda, including the 1991 Environmental Protocol to the Antarctic Treaty which establishes rules and procedures specifically designed to protect the Antarctic environment. The Protocol was ratified and went into effect in 1998. The U.S. Antarctic Program Today The U.S. Antarctic Program operates three year-round research stations and two research vessels. Additional temporary field camps are constructed and operated during the austral summer. McMurdo Station McMurdo Station (77°51' S, 166°40' E), the largest U.S. station in Antarctica, is situated on barren volcanic hills at the southern tip of Ross Island, about south of Christchurch, New Zealand and north of the South Pole. The station sits on the eastern shore of McMurdo Sound, the southernmost body of seasonally open water in the world. Mount Erebus, a high active volcano, towers over Ross Island. On the west side of the Sound, the Royal Society Range and Mount Discovery, an extinct volcano, provide spectacular vistas. The mean annual temperature is . Temperatures may reach as high as in summer and in winter. The average wind speed is , but winds have exceeded . McMurdo Sound is a historic area. In 1841, James Clark Ross brought his ships HMS Erebus and HMS Terror into the Sound, farther south than anyone had ever gone, before sailing eastward along a great wall of ice. He and his crew were the first humans to see the island and the ice shelf that both now bear his name. In 1902, Robert F. Scott wintered HMS Discovery in Winter Quarters Bay, adjacent to the station. Both of Scott's (1901–1904 and 1910–1913) and Ernest Shackleton's (1907–1909 and 1914–1916) expeditions used the area as a base to deploy sledging parties