While Mark was serving as a full-time missionary in California, the U.S. was attacked on 11 September 2001, which became one of the reasons he joined the U.S. military to fight terrorism. He received his college degree, and then enlisted in the U.S. Air Force in June 2007. He enlisted instead of becoming an officer because he knew his chances of deploying were higher as an enlisted Special Tactics airman. He wanted the toughest job the military could offer, and Air Force Combat Controller was what he was looking for.