Complex sentence: From 1951 to 1963, he was a research economist at the RAND Corporation, where he and Charles J. Hitch developed the Planning Programming, and Budgeting System (PPBS), which was first implemented by the U.S. Department of Defense in 1961.
Split into simpler sentences: From 1951 to 1963, he was a research economist with the RAND Corporation. He developed the Planning Programming and Budgetting System (PPBS), which was first implemented by the U.S. Department of Defense in 1961.