Altenburg was commissioned as a United States Army officer after law school. He was assigned to the office of the Center Judge Advocate, John F. Kennedy Special Warfare Center and School, Fort Bragg, North Carolina. After serving as a criminal defense attorney, he was the Judge Advocate, 5th Special Forces Group, and Prosecutor for the JFK Center for almost four years. He subsequently served as the Chief Prosecutor at XVIII Airborne Corps before moving to Germany for service with the 3rd Armored Division, again as Chief Prosecutor for three years.