By the 21st century, the Boeing 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 B-52H made its first flight March 6, 1961, and is still in service.