(These regulations supersede FM 100-5, Tentative Field Service Regulations, Operations, October 1, 1939.)



  1. The theater of war comprises those areas of land, sea, and air which are, or may become, directly involved in the conduct of war.

  2. A theater of operations is an area of the theater of war necessary for military operations and the administration and supply incident to military operations. The War Department designates one or more theaters of operations.

  3. A combat zone comprises that part of a theater of operations required for the active operations of the combatant forces.

    It is divided into army, corps, and division areas, each comprising the zone of operations of the unit to which it pertains.

  4. A communications zone is that part of a theater of operations, contiguous to the combat zone, which contains the lines of communication, establishments for supply and evacuation, and other agencies required for the immediate support and maintenance of the field forces in the theater of operations.

  5. The zone of the interior comprises the area of the national territory exclusive of areas included in the theater of operations.

  6. The details of organization of the theater of war and its territorial subdivisions are given in FM 100-10, FM 100-15, and in instructions relative to mobilization published by the War Department. As indicated therein, definite territorial responsibilities are assigned to GHQ, theater commanders, and army commanders.



  1. Troop organization includes command, combat (tactical), and service (administrative) elements. Most tactical units contain service elements and have some administrative functions. But a unit is not designated as administrative unless it performs all or nearly all administrative functions for its components.

  2. The field forces consist of a general headquarters (GHQ), one or more armies, the GHQ air force, an armored force, and a GHQ reserve.

  3. The GHQ air force is composed of a headquarters and a variable number of squadrons and groups of combat aviation and various other types which may be organized into wings or larger commands. It also has air base organizations comprising troops of various arms and services for security and administration.

  4. An armored force is a combined force comprising elements transported in wheeled or track-laying type motor vehicles, the bulk of which is provided either with partial or complete armor.

  5. The GHQ reserve is composed of units of the various arms and services not otherwise specifically assigned which are held for use as reinforcements or for separate missions under GHQ.

  6. Several armies may be organized into a group of armies under a designated commander. Such a group is primarily a tactical command.

  7. An army is composed of a headquarters, certain organic army troops, a variable number of corps, and a variable number of divisions, of which some or all may be assigned from time to time to corps. The army is an administrative as well as tactical unit.

  8. A corps consists of a corps headquarters, certain organic corps troops, and such infantry (cavalry, armored) divisions as may be assigned to it. The corps is primarily a tactical unit.

  9. The division is the basic large unit of the combined arms. It comprises a headquarters, infantry (cavalry)


    (armored) units, field artillery units, and certain troops of other arms and services. It is an administrative as well as a tactical unit.

  1. The term large units as used in this manual refers to divisions and larger units. A more detailed discussion of the larger units is found in FM 100-15.

  2. In each armor service, the company (troop, battery) or similar unit is the basic administrative unit. It contains all the agencies required for subsistence, interior economy, and administration. For purposes of tactical control and training, each company is subdivided into smaller units.

  3. The battalion (squadron) or similar unit is the basic tactical unit. It is composed of a headquarters, two or more companies or similar units, and certain special units, organic and attached. Unless organized as a separate battalion it has few administrative functions.

  4. The regiment is both an administrative and a tactical unit. Ordinarily, it consists of a headquarters, a headquarters company and service company, either separate or combined, and two or more battalions or similar units. It may also include a company or similar unit in which certain special weapons and means are assembled for tactical purposes, economy, instruction, and administration.

  5. A brigade is ordinarily a tactical organization composed of two or more regiments of the same arm, together with a headquarters and headquarters company or similar unit. When organized as a separate brigade it may include units of other arms and services and may have administrative functions.

  6. For organization of the Air Corps, see paragraph 76.

  7. For economy and flexibility in the assignment to tasks, the means not habitually required by a unit are pooled and organically assigned to a higher unit. These means may then be allotted to subordinate units in accordance with their requirements for particular operations.

  8. To insure unity of effort or increase readiness for combat, part or all of the subordinate units of a command may be formed into one or more temporary tactical groupings (task forces), each under a designated commander. In


    each, the unity of tactical organizations is preserved as far as practicable. In an infantry division, the term combat team is usually applied to a task force consisting of a regiment of infantry, a battalion of light artillery, and essential units of other arms in suitable proportion.

  1. The details of organization of the field forces and the amounts and kinds of transportation and major items of equipment are published in current War Department Tables of Organization and Tables of Basic Allowances. The organization of large units and pertinent technical and logistical data are given in FM 101-10.


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