From the Summary: "Since the dawn of military aviation, the U.S. military has been interested in remotely piloted aircraft. Present-day unmanned aircraft systems (UAS) typically consist of an unmanned aircraft vehicle (UAV) paired with a ground control station. UAS have become ubiquitous in U.S. military operations since the 1990s with the introduction of the MQ-1 Predator. The U.S. military currently employs several different large UAS, including  the Army's MQ-1C Gray Eagle,  the Air Force's MQ-9 Reaper,  the Navy's MQ-25 Stingray,  the Air Force's RQ-4 Global Hawk,  the Navy's MQ-4C Triton, and  the Air Force's RQ-170 Sentinel. In addition, several other reported programs are either in development or currently undergoing experimentation. These programs include the Air Force's B-21 Raider and the Air Force's RQ-180. As Congress performs its oversight and authorization functions, it may consider several potential issues associated with UAS programs, including  the cost of manned versus unmanned aircraft,  a lack of acknowledged follow-on programs of record,  the management of UAS acquisitions across the Department of Defense,  the interoperation of UAS with existing force structure, and  export controls of UAS abroad."
CRS Report for Congress, R47067
Congressional Research Service: https://crsreports.congress.gov/