The 859th Special Operations Squadron is a reserve unit of the United States Air Force. It was first activated in October 1942 as the 517th Bombardment Squadron, when the Army Air Forces replaced National Guard observation units that had been mobilized and were performing antisubmarine patrols off the Atlantic coastline. A month after its activation, the squadron was redesignated the 12th Antisubmarine Squadron. In August 1943, the Army Air forces began turning the antisubmarine patrol mission over to the Navy and the squadron moved to California, where, as the 859th Bombardment Squadron, it formed the cadre for the 492d Bombardment Group.