The head of the Department of Energy division responsible for overseeing and maintaining the U.S. nuclear weapons arsenal is stepping down, according to a statement issued on Saturday.

“The ability to serve our nation is a privilege and I have been blessed to be able to do so for many years,” wrote Tom D’Agostino, head of the National Nuclear Security Administration (NNSA).

“It has been truly an honor and privilege to serve with you and to serve the country in the wide variety of roles and opportunities I have been presented,” D’Agostino wrote in his farewell to the division.

His last day at NNSA will be Jan. 18, the final day of the Obama administration’s first term in office.