The U.S. Department of Defense (DoD) employs Unmanned Aerial Systems (UAS) across all echelons to support tactical, operational, and strategic operations. The types of UAS that are used in these operations are categorized into "Groups" according to their size and capability. Previous to 2010, UAS were categorized into "Tiers" or "Classes" separately by each branch of the military. In order to promote a homogeneous categorization, the "group system" was developed.