The eight-engine, 390,000-pound B-52 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. The B-52 entered military service in 1954. Ongoing updates have included new avionics, data-link communications, electronic defense and offensive systems, and powerful, fuel-efficient turbofan engines. It is the longest-serving bomber US military history.