Four hundred pilots and 3,600 crewmen of the 351st Bombardment Group assemble at a Colorado air base in preparation for overseas duty. The men come from all over the United States and are from many different ethnic backgrounds. When the troops arrive in England, they are welcomed by the Royal Air Force. The 351st becomes part of the 8th Air Force. By air, their base is twenty minutes away from the battlefields. The newly arrived troops begin training for battle and attend daily lectures on security. After receiving the order for their first mission, the men are briefed. They are reminded that their main job is to bring back their B-17 planes, also known as Flying Fortresses. Before the planes take off, all equipment is checked thoroughly. The planes then depart at fifteen second intervals. The first mission of the 351st is a success, as all twenty planes and all the men return. Back on base, the men clean their guns. The 351st flies many missions and downs many German planes. After each flight the men are questioned. When they are not flying, they partake in activities including games, socializing and worship. The U.S.O. brings entertainers such as Bob Hope to visit the base. At a seaside resort, the Red Cross provides the men with rest and recreation. On some missions, U.S. planes are lost, and soldiers are killed and wounded. The wounded are cared for at a nearby hospital. Sometimes the weather prevents the planes from dropping their load of bombs. In 1943, some of the pilots receive medals for exceptional service, and the base is visited by General Ira C. Eaker, commander of the 8th Air Force. The 351st participates in a big mission into Germany. After flying for about three hours, the B-17s' fighter escort turns back. As the planes get close to their target, enemy fighter planes appear. The U.S. planes drop their bombs, which include incendiary bombs and anti-personnel bombs. When the bombs are all dropped, the planes must evade flak from the ground defense. After an extensive battle, the U.S. planes return to base, ready to fight again until the war is over.
The opening credits state that the film was produced "through the cooperation of the 351st Bombardment Group, AAF." The film ends with the following written statement: "Enemy, look at these men. They're not going to lose, brother." Information provided by NARS states that General H. H. Arnold assigned Clark Gable, who was then a first lieutenant in the U.S. Air Force, to produce this film. In addition to narrating the film, Gable is seen interviewing several servicemen.