XX Bomber Command
Designated the Second Air Force on 18 September 1942, starting in mid-1943 the unit's training of B-17 and B-24 replacement crews began to be phased out, and reassigned to First, Third and Fourth Air Forces as the command began ramping up training of B-29 Superfortress Very Heavy bomb groups, destined for Twentieth Air Force. Under the newly organized XX Bomber Command, B-29 aircraft were received from Boeing's manufacturing plants and new combat groups were organized and trained. XX Bomber Command and the first B-29 groups were deployed in December 1943 to airfields in India for Operation Matterhorn operations against Japan.