Background GHQ Air Force (GHQ AF) had been established with two major combat functions, to maintain a striking force against long range targets, and the
air defense of the United States. In the spring of 1941, the
War Department established four strategic defense areas and GHQ AF reorganized its Southwest Air District as
4th Air Force with responsibility for air defense planning and organization along the west coast and in the southwest. 4th Air Force activated
4th Interceptor Command at
March Field, California on 8 July 1941, under the command of Major General
Millard F. Harmon. The command was charged with control of "active agents" for air defense in its area of responsibility, which included
interceptor aircraft,
antiaircraft artillery and
barrage balloons. Civilian organizations provided air raid warnings and enforced
blackouts and came under the authority of the
Office of Civilian Defense.
Radar was initially not sufficiently developed to be included in air defense systems, There were only ten radars to guard the Pacific coast, but the command worked "feverishly" to create a
ground observer corps and coastal radar net as elements of its Aircraft Warning Service. However, it soon became apparent that having two commands responsible for air defense in the Western Theater of Operations was impractical, and in early 1942, the 4th took over responsibility for air defense of the entire Pacific coast, replacing
2d Interceptor Command in the northwest. In June it moved its
headquarters north to
Oakland Airport, California, which was more centrally located for its increased area of responsibility. Regional air defense wings were established in August 1942 at
San Diego,
Los Angeles,
San Francisco and
Seattle Fifteen new radar sites were established, and several of the original ten were resited due to unsuitability of their locations. Coverage was extended northwards and southwards when arrangements were made for the
Royal Canadian Air Force to provide information from radar sites in British Columbia and three sites were constructed in Baja California, Mexico. With the Japanese attacks on
Midway and
the Aleutians, additional balloon and antiaircraft units were moved to the Pacific coast and the command was reinforced by units from
2nd Air Force. Additional reinforcements were prepared, but the victory at Midway led to cancellation of their movements. As the possibility of an attack on the Pacific coast grew more remote, the air defense wings became increasingly concerned with the training mission. The command continued to support the air defense mission until September 1943.
Unit and crew training In 1942, Air Force Combat Command had established an
Operational Training Unit (OTU) system for 2nd and
3d Air Forces. The system was later extended to 4th Air Force. Although it was originally intended to confine the OTU system to 2d and 3rd Air Forces, too much of the
Army Air Forces (AAF)'s aircrew and aircraft were assigned to 4th Air Force to permit the command to forego training responsibilities entirely. In May 1942, all pursuit groups assumed OTU responsibility. Even though AAF designated the units of the command to form the first "parent" and "satellite" of the program, it was not until October that Fourth Air Force even submitted a plan to operate OTUs, and not until January 1943 did the first unit, the
354th Fighter Group, begin to train under the OTU system. However, the command's training program was "seriously jeopardized" during early 1943, when
Bell P-39 Airacobras programmed for delivery to command units were diverted to the
Soviet Air Forces. Similar problems affected the command's P-38 Lightning training programs.
Curtiss-Wright AT-9 Jeeps were not available to qualify fighter pilots on twin engine operations, and during the command's active period, there were never enough P-38s on hand, requiring some fighter training for P-38 units to be conducted with single engine P-39s. Shortly thereafter, it was decided that one of the command's groups would be manned at 50% overstrength in order to train and supply replacement pilots for overseas units. This was the beginning of the
Replacement Training Unit (RTU) program, which replaced a system in which individuals were selected from existing units to fill overseas vacancies. Replacement training at
Muroc Army Air Field began in the fall. Unlike
I Fighter Command, which specialized in OTUs and
III Fighter Command, which consisted mostly of RTUs, the command's training included both types of units In time, however, the RTU program became the major type of training in all the continental air forces. As early as September 1943, Hq AAF announced that no more fighter OTUs would be formed. The last OTU fighter groups completed training early in 1944, and training turned sharply to replacement training.
Disbanding The AAF was finding that standard military units, whose manning was based on relatively inflexible
tables of organization were not well adapted to the training mission, even less so to the replacement mission. Accordingly, the AAF adopted a more functional system in which each base was organized into a separate numbered unit. In connection with this general reorganization, Fourth Air Force disbanded
IV Fighter Command and transferred its responsibilities to wings that were headquartered by AAF base units. ==Lineage==