Media related to 490th Bombardment Group at Wikimedia Commons
The squadron moved to Mountain Home Army Air Field, Idaho on 27 September 1943.
 On 1 October, it formed the cadre for the new 490th Bombardment Group.
 In early December, group headquarters and the other three squadrons of the group joined it at Mountain Home and it began training with Consolidated B-24 Liberators.
 The 851st left its training base on 9 April 1944 for the European Theater of Operations.
 The ground echelon departed the Port of Embarkation at Camp Shanks, New York, sailing on the SS Nieuw Amsterdam on 11 April and arriving in the United Kingdom  on 25 April.
 The air echelon flew its planes along the southern ferry route beginning on 12 April.

The squadron arrived at RAF Eye, its combat station, on 28 April and began combat operations on 31 May 1944.
   Its initial missions were flown to prepare for Operation Overlord, the invasion of Normandy, as the squadron concentrated on targets in France.
 It supported the landings on D-Day and attacked coastal defenses, airfields, rail lines and vehicles near the landings.
 It flew close air support missions to assist British forces near Caen in July and American forces near Brest in September.
 It was withdrawn from combat on 6 August 1944, to convert to the Boeing B-17 Flying Fortress as the 93d Combat Bombardment Wing transitioned to make the 3d Bombardment Division an all B-17 unit.

Once transition to the B-17 was completed on 24 August, the squadron concentrated on strategic bombing, attacking oil refineries, airfields, marshalling yards, and factories manufacturing aircraft and armored vehicles.
 It participated in raids against Berlin, Cologne, Hamburg, Hanover, Kassel, Merseburg and Münster.
  On occasion, the squadron was diverted from the strategic bombing campaign.
 It attacked enemy lines of communication during the Battle of the Bulge from December 1944 through January 1945.
 In the last month of the war in Europe, it carried out interdiction missions to support advancing ground forces.
 The squadron's last combat mission was flown on 20 April 1945.

Following V-E Day, the squadron carried food to flooded areas of the Netherlands and transported prisoners of war to Allied repatriation centers.
 The air echelon began flying its planes back to the United States on 6 July 1945.
  The ground echelon sailed from Southampton on the RMS Queen Elizabeth on 26 August 1945.
 The unit regrouped at Drew Field, Florida in September.
 It was inactivated there on 7 November 1945.
Media related to 490th Bombardment Group at Wikimedia Commons
The squadron moved to Mountain Home Army Air Field, Idaho on 27 September 1943.  On 1 October, it formed the cadre for the new 490th Bombardment Group.  In early December, group headquarters and the other three squadrons of the group joined it at Mountain Home and it began training with Consolidated B-24 Liberators.  The 851st left its training base on 9 April 1944 for the European Theater of Operations.  The ground echelon departed the Port of Embarkation at Camp Shanks, New York, sailing on the SS Nieuw Amsterdam on 11 April and arriving in the United Kingdom  on 25 April.  The air echelon flew its planes along the southern ferry route beginning on 12 April.
The squadron arrived at RAF Eye, its combat station, on 28 April and began combat operations on 31 May 1944.    Its initial missions were flown to prepare for Operation Overlord, the invasion of Normandy, as the squadron concentrated on targets in France.  It supported the landings on D-Day and attacked coastal defenses, airfields, rail lines and vehicles near the landings.  It flew close air support missions to assist British forces near Caen in July and American forces near Brest in September.  It was withdrawn from combat on 6 August 1944, to convert to the Boeing B-17 Flying Fortress as the 93d Combat Bombardment Wing transitioned to make the 3d Bombardment Division an all B-17 unit.
Once transition to the B-17 was completed on 24 August, the squadron concentrated on strategic bombing, attacking oil refineries, airfields, marshalling yards, and factories manufacturing aircraft and armored vehicles.  It participated in raids against Berlin, Cologne, Hamburg, Hanover, Kassel, Merseburg and Münster.   On occasion, the squadron was diverted from the strategic bombing campaign.  It attacked enemy lines of communication during the Battle of the Bulge from December 1944 through January 1945.  In the last month of the war in Europe, it carried out interdiction missions to support advancing ground forces.  The squadron's last combat mission was flown on 20 April 1945.
Following V-E Day, the squadron carried food to flooded areas of the Netherlands and transported prisoners of war to Allied repatriation centers.  The air echelon began flying its planes back to the United States on 6 July 1945.   The ground echelon sailed from Southampton on the RMS Queen Elizabeth on 26 August 1945.  The unit regrouped at Drew Field, Florida in September.  It was inactivated there on 7 November 1945.
851st Strategic Missile Squadron