Prior to joining Rising Sky, Sim had over 28 year of government service as a U.S. Army officer and subsequently as a Foreign Service Officer with the Department of State. Sim began his military career as a Signal Corps officer serving in a variety of posts and assignments, eventually retiring after twenty years of active-duty service in 2011. During this time, he was assigned to a variety of stateside posts as well as overseas assignments in Germany and Italy. Additionally, he deployed seven times for operational peacekeeping, humanitarian, and/or wartime operations, including Somalia, Cuba, Kosovo, Kuwait, Iraq and Afghanistan. He finished his military career as an operational planner, assigned as Chief of Plans for US Army Central Command.

He subsequently joined the U.S. Department of State serving a Foreign Service Officer with assignments in Tegucigalpa, Honduras; Guayaquil, Ecuador; and Washington DC where he served in the Bureau of European and Eurasian Affairs and the Bureau of Political-Military Affairs.