Former Defense Secretary Harold Brown dies at 91

Brown played a crucial role in the Carter administration's effort to end the Iranian hostage crisis, and described the botched 1980 rescue attempt as the biggest regret of his career.

"The failure to rescue the U.S. hostages still haunts me," Brown wrote in his memoir "Star Spangled Security," according to the RAND Corporation, a think tank where Brown served on the board of trustees for decades.

It announced his passing Saturday and detailed his life and career as a nuclear physicist, weapons designer, California Institute of Technology president, philanthropist and public servant.

Before he became the the 14th defense secretary, Brown served as the Air Force secretary under Lyndon Johnson during a period that included the US bombing of North Vietnam.

"Harold Brown understood, perhaps better than any defense secretary before him, the technological complexities and unprecedented dangers of modern warfare," said Michael D. Rich, president and chief executive officer of the Santa Monica, California-based RAND Corporation. "He was also an educator and author who made tremendous contributions to the advancement of science and the security of the nation."

Brown was awarded the Presidential Medal of Freedom by Jimmy Carter, the nation's highest civilian honor, and the Enrico Fermi Award for achievement in science and technology by President Bill Clinton.