It served in the European Theater of Operations, where it participated in the strategic bombing campaign against Germany and earned two Distinguished Unit Citations for its combat actions.

[1] On 1 November, the squadron moved to Pocatello Army Air Field, Idaho, where it began to act as a Operational Training Unit.

The ground echelon left Pyote on 16 April for Camp Kilmer, New Jersey in the New York Port of Embarkation, sailing on the RMS Queen Elizabeth on 5 May and arriving in Scotland on 13 May.

[6] The squadron was established at RAF Great Saling by 12 May, and flew its first combat mission the next day, an attack against the airfield at Saint-Omer, France.

It attacked airdromes, aircraft factories, harbors, oil refineries, railway yards, shipyards, and other industrial targets in Germany, France, the Netherlands, Belgium, Norway, Poland, Hungary, and Czechoslovakia.

Targets included airfields at Bordeaux and Augsburg; marshalling yards at Kiel, Hamm, Braunschweig, and Gdynia; aircraft factories at Chemnitz, Hanover, and Diósgyőr; oil refineries at Merseburg and Most, and chemical works in Wiesbaden, Ludwigshafen, and Neunkirchen[5] During an attack on the Messerschmitt factory at Regensberg on 17 August 1943, the squadron was without escort after its escorting Republic P-47 Thunderbolts reached the limit of their range.

[5][9] The squadron formed part of the leading 45th Combat Bombardment Wing formation on very long-range mission against the Focke-Wulf Fw 190 factory at Poznań.

In the preparation for Operation Overlord, the invasion of Normandy, it bombed coastal defenses, railway bridges, gun emplacements, and field batteries in the battle area prior to and during D-Day in June 1944.

[5] After V-E Day, the 337th flew food missions to the Netherlands and hauled redeployed personnel to French Morocco, Ireland, France, and Germany.