Complex sentence: In the summer of 1961, a complete reorganization of the base began in order to convert the base from the B-47 Stratojet medium jet bomber to B-52 "Stratofortress" heavy bombers.
Split into simpler sentences: In the summer of 1961, a complete reorganization of the base began. A program began to convert the base from the B-47 Stratojet medium jet bomber to B-52 "Stratofortress" heavy bombers.