輜重兵
A graduate of Wheaton College, which he attended on an Army Reserve Officer Training Corps scholarship, Coffin was commissioned as an officer in the Quartermaster Corps in December 1981. He was the group supply maintenance officer and logistics plans officer at Army Special Operations Forces Europe from 1982 to 1985. He was watch commander at the United States Space Command and North American Aerospace Defense Command from 1996 to 1999, when he joined the United States Army Space and Missile Defense Command (USASMDC) staff as the G-4 (Logistics Officer) . He subsequently became commander of the 1st Space Battalion. He was deployed to Afghanistan in support of Operation Enduring Freedom as chief of the U.S. Strategic Command Forward Integration Team, Kandahar Air Field, from July 2010 to January 2011, and was Deputy Commanding General for Operations of USASMDC from 2011 to 2014.