After it became operational in 1955, the B-52 remained the main long-range heavy bomber of the U.S. Air Force during the Cold War, and it continues to be an important part of the USAF bomber force today. Nearly 750 were built before production ended in Oct. 26, 1962; 170 of these were B-52Ds. The B-52 has set numerous records in its many years of service. On Jan. 18, 1957, three B-52Bs completed the first non-stop round-the-world flight by jet aircraft, lasting 45 hours and 19 minutes and requiring only three aerial refuelings. It was also a B-52 that made the first airborne hydrogen bomb drop over Bikini Atoll on May 21, 1956. In June 1965 B-52s entered combat in Southeast Asia. By August 1973, they had flown 126,615 combat sorties with 17 B-52s lost to enemy action. The B-52D on display at the National Museum of the United States Air Force saw extensive service in Southeast Asia and was severely damaged by an enemy surface-to-air missile on April 9, 1972. In December 1972, after being repaired, it flew four additional missions over North Vietnam. Transferred from the 97th Bomb Wing, Blytheville Air Force Base, Ark., this aircraft was flown to the museum in November 1978.