Harold Brown, an advocate of nuclear arms control who as President Jimmy Carter’s Defence Secretary tried but failed to win US Senate approval of a key treaty with the Soviet Union, has died at age 91, the think tank where he worked said.

Brown, a native New Yorker, was the first scientist to take the helm of the large and complex US military establishment. He was a physicist who received his bachelor’s degree at age 18 and his doctorate at 22. Brown spent his professional life initially developing nuclear weapons and then later striving to control them.

“Brown understood, perhaps better than any Defence Secretary before him, the technological complexities and unprecedented dangers of modern warfare,” RAND president and chief executive officer Michael D Rich said. “He was also an educator and author who made tremendous contributions to the advancement of science and the security of the nation.”

“The world is a dangerous place. But it has always been a dangerous place,” Brown told The Washington Post in 1980. “All we’re offered is a reasonable change to make things work. Because I’m temperamentally an optimist, I believe that’s good enough.”

Brown became Pentagon chief in 1977 and left in 1981, disappointed that was unable to convince the Senate to back the nuclear arms limitation treaty reached with the Soviet Union in 1979 dubbed SALT II. As Defence Secretary, he also was involved in planning the botched US military mission to rescue American hostages held in Iran that ended with the deaths of eight US service members in April 1980 and the diminishment of US prestige.