Since Pres. Harry Truman established the Nevada Test Site (NTS) in December 1950, it has played a vital role in the security of the United States. For four decades, the test site's primary purpose was developmental testing of nuclear explosives. Atmospheric tests conducted over Yucca Flat and Frenchman Flat between 1951 and 1962 involved thousands of Army troops and Marines simulating nuclear battlefield conditions. Civil defense planners studied blast and radiation effects and evaluated bomb shelter designs. Testing moved underground in 1963 to eliminate radioactive fallout. Other projects at the NTS included nuclear rocket engine development for space travel, training for NASA's Apollo astronauts, excavation experiments, radioactive waste storage studies, and aircraft testing. Since the last underground nuclear test in 1992, this geographically diverse testing and training complex north of Las Vegas—known since 2010 as the Nevada National Security Site—has been used to support nuclear stockpile stewardship and as a unique outdoor laboratory for government and industry research and development efforts.