The KB-50 tanker was a later version of the four-engine, propeller-powered B-50 bomber which first flew in 1947. The B-50, among the last piston-powered bombers built during an era that was to be dominated by jets, evolved from the B-29D. However, because it included so many improvements, it was redesignated the B-50A with 59 percent more power than the B-29. Two 5,200-pound-thrust jet engines enhanced the B-50’s speed when it was converted to the hose-type KB-50 aerial tanker, so it could refuel jet aircraft flying at 400 mph. Some KB-50s served until 1965 and were in action during the Vietnam conflict as refueling tankers.