On December 31, 1956, a charter was issued specifying the Board as advisory to the Assistant Secretary of Defense (Research and Development). Following the consolidation of the offices of the Assistant Secretaries of Defense for R&D and Applications Engineering in 1957, the Board reconstituted as advisory to the Secretary of Defense through the Assistant Secretary of Defense (Research and Engineering). Its membership was increased to 28, including as ex officio members, the Chairmen of the President's Science Advisory Committee and the Scientific Advisory Committee in the Office of Guided Missiles, Office of the Secretary of Defense (OSD). A revised Board charter was issued on October 30, 1957.