The 561st was first activated as the 561st Bombardment Squadron at Gowen Field, Idaho, one of the four original squadrons of the 388th Bombardment Group, in December 1942. The cadre that formed at Gowen moved to Wendover Field, Utah in February 1943, where the unit was fully manned and squadron training with Boeing B-17 Flying Fortress heavy bombers began. Training continued until June 1943, when it deployed to England. The air echelon ferried its B-17s to England via the northern ferry route, while the ground echelon departed for Camp Kilmer, New Jersey, the port of embarkation, sailing in the on 1 July.