 About one year later, SAC set plans in motion to replace the 28th's B-36s with the new all-jet B-52 Stratofortress.The last B-36 left Ellsworth on 29 May 1957 and the first B-52 arrived sixteen days later.In 1958, all base units came under the command of the 821st Strategic Aerospace Division, headquartered at Ellsworth.