 Nearly all new heavy bomb groups organized after Pearl Harbor were organized and trained at Second Air Force Bases, by II Bomber Command operational training units (OTU) then were deployed to combat commands around the world.McChord trained numerous bombardment squadrons during the war, receiving graduates of AAF Training Command's flight and technical schools and forming them into operational squadrons which were then sent on to second and third phase training prior to being deployed to the overseas combat air forces.Starting in mid-1943 the training of B-17 and B-24 replacement crews began to be phased out, as the Second Air Force began ramping up training of B-29 Superfortress Very Heavy bomb groups, destined for Twentieth Air Force.