Brown died on Friday January 4 2019 at his home in Rancho Santa Fe, Calif. He was 91. His daughter Deborah Brown said the cause was pancreatic cancer. Born in New York City on 19 September 1927, Brown took three degrees at Columbia University, including, at age 21 in 1949, a Ph.D. in physics. After a short period of teaching and postdoctoral research, Brown became a research scientist at the University of California Radiation Laboratory at Berkeley. In 1952 he joined the staff of the Lawrence Radiation Laboratory at Livermore, California, and became its director in 1960. During the 1950s he served as a member of or consultant to several federal scientific bodies and as senior science adviser at the 1958-59 Conference on the Discontinuance of Nuclear Tests. Brown worked under Robert McNamara as director of defense research and engineering from 1961 to 1965, and then as secretary of the Air Force from October 1965 to February 1969. Between 1969 and 1977 he was president of the California Institute of Technology. With almost eight years of prior service in the Pentagon, Brown was the first scientist to become secretary of defense. After leaving the Pentagon in 1981, Mr. Brown taught at the Paul H. Nitze School of Advanced International Studies at Johns Hopkins University for several years, and from 1984 to 1992 he was chairman of the school’s foreign policy institute. Since 1990, he had been a partner at Warburg Pincus, the New York investment firm. He served on the boards of many companies, including Altria, CBS, IBM, Mattel and Rand. In addition to his daughter Deborah, he is survived by another daughter, Ellen Brown; a sister, Leila Brennet; and two grandchildren.