The four-engine, propeller-powered B-50 bomber, which first flew in 1947, was among the last piston-powered bombers built during an era that was to be dominated by jets. However, in 1949, the B-50A, the Lucky Lady II, made the first nonstop flight around the world in 94 hours, refueled in flight four times by KB-29Ms. The B-50 originally evolved from the B-29D but because it included so many improvements, it was redesignated the B-50A, with 59 percent more power than the B-29. The next version, the B-50B, fitted with cameras and wing tanks, was designated RB-50B and used for strategic reconnaissance. The B-50D, the most common variant, was distinguished by a one-piece transparent-plastic nose molding and an optically flat bombardier’s window in the lower portion. Some B-50s were later converted to hose-type KB-50 aerial tankers, their speed enhanced by the addition of two 5,200-pound-thrust jet engines, so at 400 mph, they could refuel jet aircraft. One KB-50D became a drone to test Bell XGAM missiles and 36 became long-range reconnaissance aircraft (WB-50D).