Ash Carter, who served as defence secretary for the last two years of the Obama administration, has died at age 68. During that time, he removed a prohibition on transgender persons serving in the military and opened combat professions in the military to women.

According to a statement released on Tuesday by Douglas Elmendorf, dean of Harvard University’s Kennedy School, Carter passed away following a heart attack on Monday night. The school’s Belfer Center for Science and International Affairs had been directed by Carter.

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Carter managed the department’s campaign to expedite the delivery of more than 24,000 Mine Resistant Ambush Protected vehicles to Iraq and Afghanistan while working as the senior procurement officer in President Barack Obama’s administration before being nominated the secretary of the Defense Department.

Thousands of American soldiers were being injured or killed at the time as a result of roadside bombs because the trucks they were driving lacked sufficient safety measures. Carter usually cited the quick creation and acquisition of those vehicles as one of his greatest successes.

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“At peak production, the United States shipped over 1,000 MRAPs a month to theater. And there, they saved lives,” Carter said at a 2012 ceremony marking the completion of the vehicle production. “And you all know me, I would have driven one in here today, if I could get it through the door.”

After three years of research and discussion, Carter ordered the military to allow women to work in any position, even the most hazardous and taxing commando positions, in December 2015. This ended the last remaining obstacle to women fighting in combat.

The next year, Carter lifted the ban on transgender service members in the American military, claiming that doing so was morally correct.

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“Americans who want to serve and can meet our standards should be afforded the opportunity to compete to do so,” Carter said in June 2016, laying out a one-year plan to implement the change. “Our mission is to defend this country, and we don’t want barriers unrelated to a person’s qualification to serve preventing us from recruiting or retaining the soldier, sailor, airman, or Marine who can best accomplish the mission.”

Carter, a Philadelphia native, served at the 25th defense secretary and “loved nothing more than spending time with the troops, making frequent trips to Iraq and Afghanistan to visit U.S. forces with his wife Stephanie,” his family said in a statement. “Carter always set politics aside; he served presidents of both parties over five administrations.”