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.

After deploying to England, the 492d entered the strategic bombing campaign against Germany, but in three months of combat, suffered the most severe losses of an Eighth Air Force bomber group.

The 492d Group was withdrawn from combat in August 1944, and the 859th moved on paper to replace the 788th Bombardment Squadron, which was engaged in Operation Carpetbagger, dropping agents and supplies behind German lines, primarily in France.

It was initially equipped with the Stinson Vigilants, Douglas O-46s and North American O-47s of the 104th Observation Squadron, which it replaced at Atlantic City.

[13] The squadron flew its first combat mission on 11 May 1944, joining the strategic bombing campaign with attacks primarily on targets in central Germany.

During the first week in June, the squadron was diverted from strategic targets to support Operation Overlord by attacking airfields and V-1 flying bomb and V-2 rocket launch sites.

It bombed coastal defenses in Normandy on D-Day, 6 June 1944, and continued interdiction attacks until the middle of the month.

Except for support of Operation Cobra, the breakout at Saint Lo, the squadron then resumed bombardment of strategic targets in Germany.

With the drawdown of the Carpetbagger mission, the squadron concentrated on hauling gasoline to advancing mechanized forces in France and Belgium.

[4][11][19] During its assignment to special operations form England, the squadron flew 179 sorties and delivered 121 "Joes", as the agents were called.

Most supply drops were made in the Zagreb region, where partisans were attacking German forces withdrawing up the Sava River valley.

[4] The unit was reactivated in the Air Force reserve as the 859th Special Operations Squadron, marked by a ceremony at Duke Field, Florida, on April 1, 2016.