Replaced the propeller-driven B-29s and B-50s with new B-47E Stratojet swept-wing medium bombers in 1954, capable of flying at high subsonic speeds, primarily designed for penetrating the airspace of the Soviet Union. The 43rd set a new, jet endurance record in 1954 by keeping a B-47 airborne for 47:35 hours. Flew numerous training missions and participated in various SAC exercises and deployments with the Stratojet during the 1950s. In the late 1950s, the B-47 was considered to be reaching obsolescence, and was being phased out of SAC's strategic arsenal. The 43rd began reassigning its Stratojets to other wings as replacement aircraft beginning in 1959.