There is a natural bond of brotherhood among former Secretaries of Defense (there have been 26 of them, Jim Mattis joining most recently), and I benefited from their private counsel and support when I had that job.
Harold Brown, Jimmy Carter's SECDEF, and I had a special connection: the day I was confirmed, Harold called me and said jokingly, "Ash, every 20 years the country gets a good Secretary." What he meant by 'good' was a scientist: Brown and I were physicists, William Perry (1990s SECDEF) a mathematician. I met Harold in 1980 when I was working on my very first defense technology program. He had already been SECDEF, President of Cal Tech, Secretary of the Air Force, Director of Defense Research and Engineering, and Director of the Lawrence Livermore nuclear weapons laboratory. Yet he took the time to encourage me to stay involved in defense, and I did.
Harold's tenure as SECDEF was marked by major accomplishments. The Cold War was raging, and Harold funded the new Trident SLBM and MX ICBM to ensure deterrence, while secretly starting the stealth bomber program and also supporting intermediate range nuclear forces to counter similar Soviet developments, at the same time supporting arms control agreements. A whole host of innovations we now take for granted as part of the defense landscape -- cruise missiles, GPS, precision bombs, and more -- grew up during Harold's tenure.
Harold was in the long and unbroken string of SECDEF's stretching to the present day who supported a strong NATO alliance while also bearding the allies to spend more. During his time the transition began in earnest from the Vietnam era draft to the high quality all-volunteer military that shines today.
On the pol-mil front other than the Cold War, there were successes during Harold's time: the Camp David Accords and resolution of the thorny Panama Canal issue, as well as persuading President Carter not to diminish the U.S. military presence on the Korean Peninsula. Most important for the long run was establishing a defense relationship with a China that was newly opening up. There were failures too: the Iran hostage-rescue attempt was a debacle but had at least the long term salutary effect of spurring the creation of a Special Operations Command and the long pedigree of successful raids and rescues we have conducted in Iraq, Afghanistan, Syria, and elsewhere in recent years -- notably the bin Laden raid. The Shah of Iran fell to the mullahs and the Soviets invaded Afghanistan during the same years, but they at least led to the creation of CENTCOM.
Harold Brown represented rigor and truth in the grave matter of protecting America, civility and decency in conduct, and adherence to long-standing bipartisan security commitments around the world. These commitments have characterized the department to this day, which gives me great faith in the future.
Carter, Ash. “Ash Carter: Remembering Harold Brown.” Belfer Center for Science and International Affairs, Harvard Kennedy School, January 5, 2019