Sims was commissioned as a
second lieutenant in 1991 after graduating from the
United States Military Academy with a
Bachelor of Science degree in
political science. His education also includes a
Master of Arts degree in management from
Webster University, the
United States Army Basic and Advanced Infantry Officer Courses, and the
United States Army Command and General Staff College. From November 1991 to April 1994 he was a platoon leader in the
505th Infantry Regiment,
82nd Airborne Division, at
Fort Bragg,
North Carolina, and then until August 1995 he was a platoon leader in the
75th Ranger Regiment at
Fort Lewis,
Washington. Sims was a student at the United States Army Infantry School at
Fort Benning,
Georgia, between 1995 and 1996, and became an assistant professor of military science at the
University of Pittsburgh in
Pennsylvania from April 1996 to May 1998. He was then a battalion headquarters company commander in the
501st Parachute Infantry Regiment,
172nd Infantry Brigade, at
Ford Richardson,
Alaska, until February 2000. Between March 2000 and May 2001 Sims became the commander of C Company in the
3rd Infantry Regiment (The Old Guard), at
Fort Myers,
Virginia, and then the regimental assistant operations officer. After that, he was the
aide-de-camp to the commanding general,
United States Army Military District of Washington at
Fort McNair,
Washington, DC, until July 2002. and took up the post in January 2024. Despite his nomination by the Army for his fourth star, defense secretary Pete Hegseth removed his nomination allegedly based on Sims’s previous work for General
Mark Milley, a former Chairman of the Joint Chiefs, Sims retired from the Army at the end of September 2025, with over 34 years of service. ==Dates of promotion==