By the 21st century, the B-52 was in its fifth decade of operational service. The eight-engine, 390,000-pound jet was the country's first long-range, swept-wing heavy bomber. It began as an intercontinental, high-altitude nuclear bomber, and its operational capabilities were adapted to meet changing defense needs. B-52s have been modified for low-level flight, conventional bombing, extended-range flights and transport of improved defensive and offensive equipment -- including ballistic missiles that can be launched hundreds of miles from their targets. The original XB-52 design, selected by the Army Air Force in 1946, was for a straight-wing, six-engine, propeller-powered heavy bomber. However, the Air force approved the company's request to develop an entirely new jet bomber under the same designation. Throughout the 1950s, the B-52 chalked up numerous distance and speed records. It cut the round-the-world speed record in half, and in January 1962, it flew 12,500 miles nonstop from Japan to Spain without refueling. This flight alone broke 11 distance and speed records. B-52s saw active duty in the Vietnam War, were used in the Persian Gulf War in 1991 and over Afghanistan in 2001.