- The Army has always divided its organizations between those that perform specific tasks and tactical units operating in the field. During the nineteenth century the Army called these categories staff and line. The staff consisted of various departments and corps, including The Adjutant General's Department, Quartermaster Department, Medical Department, Corps of Engineers, Ordnance Department, and Signal Corps. The line consisted of cavalry, artillery, and infantry regiments. The former may be considered the predecessors of today's TDA units, while the latter may be thought of as today's table of organization and equipment (TOE) units. Personnel from both staff and line manned installations and geographic departments. Congress directly authorized personnel for the line regiments, and their personnel "tables" were included in the public statutes. This system of designating the internal structure of line units continued to be part of the statutes as late as the National Defense Act of 1916. While Congress also authorized the strength and structure of the corps and departments in public statutes, additional personnel for these staffs came from men detailed from the line regiments and from civilian employees.
- During the early years of the twentieth century, although no line units above the regimental level were authorized except during wartime, the Army staff began planning for higher-level organizations in the event of war. Tables of organization were included in Field Service Regulations, published in 1905, for both line regiments and for echelons above the regimental level, i.e. divisions, corps, and field armies. Units above the regimental level continued to be manned provisionally. Tables of organization, similar to those in use today, were first published in 1914.
- Tables of organization and tables of allowances (equipment) were published separately until 1943, when they were consolidated as tables of organization and equipment (TOEs). Tables of allowances were also published for installations, schools, departments, etc., and in 1936 the term "table of distribution" was adopted for the document that authorized personnel for such units. In 1943 the tables of distribution and tables of allowances were also consolidated into tables of distribution and allowances (TDAs).
- TDA units are organized to perform specific missions for which there are no appropriate TOEs and are discontinued as soon as their assigned missions have been accomplished. Unlike TOE units, TDA organizations are considered non-deployable, even when organized overseas, as their missions are normally tied to a geographic location. The personnel of TDA organizations can be military, civilian, or a combination of both. In some instances, provisional-type units have been organized under TDAs until suitable TOEs were established. Examples are some of the mobile army surgical hospitals (MASHs) and a ranger company organized in Korea during the Korean War. When the Army developed TOEs, the TDA organizations were discontinued.
- A TOE prescribes the normal mission, organizational structure, and personnel and equipment requirements for a military unit and is the basis for an authorization document. Units are constituted and activated in accordance with an approved TOE or modified TOE. All personnel are military, and the unit can be deployed anywhere in the world. Some current TOE organizations have TDA augmentations, which may include civilians and foreign personnel, to assist in performing their non-tactical missions. These augmentations are not deployable, however.
- Although TDA and TOE units are distinct types of organizations, there are some instances in which either could be used, the military police company at a garrison or installation, for example. A TOE military police company can perform the function, but such units are deployable, and in the event of war the post conceivably might be left without military police support. If the post TDA includes the military police function, then the personnel and equipment authorizations remain with the post regardless of war or other contingencies.
- The sustainment base of the Army is made up of TDA-type units, and the number of personnel assigned to them fluctuates. In 1905 34 percent of officers in the Regular Army were assigned or detailed to organizations other than line units. The number had risen to 45 percent by 1911 and to approximately 50 percent by 1921. Throughout the 1930s the number of officers in TDA-type units remained at about 60 percent of the authorized officer strength. With the mobilization of forces in 1940-41, this percentage dropped to about 45 percent. In June 1989, as the Army began its current reduction, the Active component had 55 percent of its authorized officer strength (43,929 of 80,066), 24 percent of its authorized warrant officer strength (3,474 of 15,415), 22 percent of its authorized enlisted strength (126,195 of 578,322), and almost 100 percent of its authorized civilian strength (397,783 of 397,790) in TDA units.
Prepared by DAMH-FPO/30 May 1995