NASA WAS FORMALLY ESTABLISHED on October 1, 1958. An aeronautical research agency, the National Advisory Committee for Aeronautics (NACA) was reorganized and became the nucleus of the new organization. At that time the space program had already begun. Sputnik I had been launched by the U.S.S.R. on October 4, 1957, a year earlier. This was followed by Sputnik II, launched November 3, 1957. The U.S. Navy attempted to launch Vanguard satellites on December 6, 1957, and February 5, 1958. They succeeded on March 17, 1958. Meanwhile, on January 31, 1958, the U.S. Army had launched Explorer I whose instruments discovered the Van Allen belt. The U.S. Air Force attempted its first lunar probe with Thor-Able I on August 17, 1958, but failed. The Department of Defense Advanced Research Programs Agency (ARPA) had taken over the Explorer program with the successful launch of Explorer 4 on July 26, 1958. After the establishment of NASA, these military projects passed into civilian control.