1. Security embraces all measures taken by a command to protect itself against annoyance, surprise, and observation by an enemy.

  2. The primary mission of a security detachment is to protect the command against surprise attack and observation by hostile air and ground forces, and to maintain freedom of maneuver for the command by gaining the time and space it requires to make the necessary dispositions. Forces assigned to security missions are secondarily charged with reconnaissance.

  3. Adequate and timely information is the basis of all security measures.

  4. Security and reconnaissance forces operate in accordance with different considerations. In general, security forces operate primarily with reference to the command to be secured; reconnaissance forces operate primarily with reference to the enemy.

  5. Each commander is responsible for the security of his command. This includes the protection of his lines of communication unless such protection is furnished by the higher commander. The superior commander prescribes security measures for the protection of the command as a whole or coordinates those adopted by subordinate commanders. Subordinate commanders provide such additional security as is required for their own local protection. The measures adopted are appropriate to the hostile threat. As the danger becomes greater, as, for example, when contact is imminent, security measures are increased.

  6. All security measures include an adequate warning system consisting of observers and the means of signal communication to warn promptly of hostile dispositions and operations on the ground and in the air. Special measures are taken to warn of the approach of hostile mechanized or air forces.


  1. Security detachments weaken the available forces of a command and in some situations constitute a partial commitment of the command to action. They are given sufficient strength to preserve the commander's freedom of action, and no more. In their composition, consideration is given to the desirability of preserving tactical unity. It is desirable that they possess mobility at least equal to that of the forces they are expected to oppose.

  2. In proximity to the enemy, an advancing force secures itself to the front by mobile reconnaissance elements sent out in advance of the command and by an advance guard.

  3. Depending upon the composition of the command, the mobile reconnaissance elements vary from armored units, cavalry, and aviation, in the case of large units, to small cavalry detachments, motorcyclists, or infantry in trucks, in the case of small units.

  4. The advance guard consists of a fraction of the command sent out on the route or routes of advance in front of the main body to protect it against surprise and observation, to clear the way by driving back weak enemy forces, removing obstacles, and repairing demolitions, and to secure for the main body the time and space required for its deployment for action in accordance with the plan of the commander. (For details, see ch. 8.)

  5. A command retiring in the presence of the enemy secures itself by a rear guard, a fraction of the command which follows the main body within the zone of retirement, usually by bounds, for the purpose of protecting it against hostile pursuit. (For details, see ch. 11.)

  6. An advancing force threatened in rear by hostile mobile forces also requires a rear guard. In the same way, a retiring force confronted with the danger of interception by hostile encircling forces requires an advance guard.

  7. In addition to its advance or rear guards, a command whose flanks are not protected by adjacent units will often find it necessary to detail flank guards to protect the exposed flanks. (See ch. 8.)

  8. A resting or defending force secures itself by an outpost, a fraction of the command disposed to cover its front,


    flanks, and rear when the situation indicates, to protect it against surprise attack and observation by hostile ground forces. (For details, see ch. 7.)

  1. There is a similarity in the formation of advance, flank, and rear guards and outposts. Each comprises reconnaissance groups which send out patrols or post sentinels for observation. These reconnaissance groups are backed up by a support echelon, the principal element of resistance. In large security detachments, a reserve is provided. The reserve constitutes the principal maneuvering and reinforcing element for offensive or defensive action as determined by the mission of the security detachment, which mission in turn depends upon the plan for the subsequent employment of the command as a whole.

  2. An echelon of command which depends upon another for security to its front, flanks, or rear is responsible for maintaining contact with the unit upon which it depends. This is accomplished by means of liaison agents which it sends to the unit upon which it depends for the purpose of gaining information of the situation and by means of combat patrols which move between the two to assure connection.

  3. Reconnaissance and observation aviation, and in many situations combat aviation, is allotted in sufficient strength to supplement effectively the ground security forces. Combat aviation is particularly effective in providing security for fast moving and often isolated mechanized forces against hostile air and ground attack.


  4. Terrain and the road net influence the employment of mechanized forces. A map study, supplemented by air and ground reconnaissance, will disclose avenues of approach which may favor or impede mechanized operations. Reliance for protection against mechanized attack cannot be placed on terrain alone. When approaches are favorable, special measures are taken for antimechanized protection, especially by exposed march columns.

  5. Security against mechanized units requires an efficient warning system, which includes an intelligence and a signal communication system carefully coordinated to insure early


    and continuing information of the presence and action of hostile mobile forces. Timely warning permits an increased readiness for action. Mechanized reconnaissance detachments operating well to the front and flanks are especially suitable for giving warning. All observation and reconnaissance agencies, both ground and air, are required to make an immediate report of a mechanized threat to the nearest commander. In addition to security measures adopted by a command as a whole, subordinate units conduct local reconnaissance to prevent surprise mechanized attack.

  1. The means for protection against mechanized attack are active and passive. The active means include antitank guns, artillery, combat aviation, antiaircraft artillery which is capable of firing at horizontal or minus elevations, tank units and armored divisions, chemicals, and individual weapons to the limit of their effectiveness. Passive means include reconnaissance, concealment, cover, natural and artificial obstacles, buildings, demolitions, antitank mines, and organized localities. Usually active and passive means are used in combination.

  2. Security against mechanized attack must be organized from two standpoints--the local protection of the troops and the protection of the command as a whole. The first is the mission of the antitank weapons organically assigned to lower units.

    The second is the mission of the antitank units at the disposal of the higher commander. These units, because of their great mobility, are available for employment at a distance from the command or for concentration at the decisive locality. Mobile units capable of effective employment against mechanized forces are held for maneuver against hostile mechanized vehicles which succeed in breaking through. To insure the prompt transmission of information and orders to units, arrangements are made for rapid means of signal communication with them.

  3. The coordination of the means of antimechanized protection is a command responsibility. Commanders of subordinate units are given missions for antimechanized defense which are specific with respect to time, place, and purpose, and cooperation with other units, but which leave to them the details of execution. (See ch. 10.)



  1. It is the responsibility of each commander to take measures to provide security for his command against chemical agents.

  2. The means of providing security against chemical attack consist of an adequate warning system, the provision of individual and collective protective equipment, provision for the prompt decontamination of individuals, equipment, and supplies, and tactical measures which minimize the effects of chemical agents.

  3. An adequate warning system comprises reconnaissance to locate and define contaminated areas, gas sentinels, and an alarm system to alert the command when a chemical attack begins or impends.

  4. Individual equipment consists principally of gas masks and protective clothing. Men must be trained and disciplined in the use of this equipment. Failure in this respect results in excessive casualties and incurs the danger of panic.

  5. Collective equipment includes gasproof shelters, or protective covers for equipment and supplies, and decontaminating equipment and supplies. Gasproof shelters are provided in all permanent fortifications; their use in field fortifications increases with the elaboration of the field fortifications.

    Prompt decontamination of individuals, equipment, supplies, and occupied areas reduces casualties and losses of equipment and supplies.

  6. Tactical measures include troop dispositions which take advantage, as far as practicable, of terrain unfavorable for gas concentrations and the avoidance or evacuation, to the extent possible, of gassed areas. Alternate positions for units and supporting weapons are selected in advance.


  7. Regardless of the effectiveness of the security measures taken by the higher command through the offensive action of its combat aviation, all units must consider the probability of air attack and reconnaissance and provide appropriate security measures.


  1. Measures taken by ground troops for antiaircraft security vary with the situation, the degree of visibility, the concealment and cover offered by the terrain, and the capabilities of the enemy's aviation. Protective measures comprise warning, concealment, dispersion, and fire.

  2. The first requirement of antiaircraft security is an efficient warning system. Air guards are detailed by all units to give timely warning of the approach of hostile aviation. In addition, an aircraft warning service is, whenever practicable, organized within an area for the purpose of detecting and tracing movements of hostile air forces and transmitting warning of the approach and departure of such forces.

  3. Upon receiving an air alarm signal, troops in position, bivouac, or billets seek the nearest concealment or cover and remain motionless. In general, foot troops on the road take concealment or cover in adjacent ditches, depressions, or shadows. Motorized troops clear the center of the road, halt, and dismount. Horse elements seek protection by dispersal and the utilization of all available concealment and cover. When secrecy is not of paramount importance, all suitable weapons are employed against low flying aircraft.

    When the situation indicates the necessity for continued movement and a command is subjected to frequent air attacks, maximum advantage is taken of dispersion and available concealment and cover without unduly delaying the movement. Troops must be prepared to accept some casualties rather than delay arrival at their destination at the appointed time.

  4. Measures taken for concealment aim to defeat both visual reconnaissance and air photography. Protective measures taken to defeat the camera will ordinarily deceive the eye of the air observer.

    The presence and position of troops are disclosed to an air observer by movement, by regular formation or outline, by reflection of light, or by dust, smoke, or newly made tracks and entrenchments. All commanders are required to take appropriate countermeasures to prevent detection.

  5. Shadows cast by the sun early in the morning and late in the afternoon facilitate concealment. Ground haze or mist may constitute an effective screen against air ob-


    servation. A low ceiling makes air reconnaissance dangerous for the air observer. During darkness, blackout frequently provides effective concealment.

    Woods and villages afford concealment from air observation and reconnaissance; they serve to screen troops in shelter, in assembly, in position, and in movement.

    Intrenchments and field works are visible from the air unless carefully sited and camouflaged. Protection is sought by the distribution of the defenses on the terrain and by their adaptation to concealment and cover such as buildings, brush, hedges, banks, ditches, and cuts.

  1. A command diminishes its vulnerability to air observation and attack by adopting dispersed formations. Dispersion in formation may be accomplished by increased width and depth of dispositions, by reduced density within columns or groups, and by increased speed in movement between successive terrain lines affording concealment or cover.

  2. The antiaircraft security of a column depends initially on the efficacy of the concealment in its last bivouac. During a movement, the important periods during which antiaircraft security must be provided are the formation of the march column, the passage of defiles or crossings en route, and the movement into shelter or assembly positions at the end of the march. During temporary halts, troops and vehicles clear the road and take full advantage of all nearby cover.

  3. At night, special precautions must be taken against reconnaissance by hostile aviation using flares. When a unit is illuminated it halts and remains motionless. No lights visible to air observers are permitted to be used by troops and vehicles.

  4. All units take measures for immediate protection against low-flying aircraft by using their own weapons which are suitable for fire against aircraft. All troops charged with this duty are constantly prepared for immediate action. Antiaircraft artillery reinforces the antiaircraft fire of other units and operates especially against aviation flying beyond the effective range of weapons of other arms.

  5. In the forward area of the combat zone, antiaircraft artillery protects the principal troop concentrations and


    assembly positions, and covers the movement of troops through defiles and critical localities. Driving hostile aviation to higher altitudes decreases the effectiveness of air attack and observation. Since antiaircraft artillery will be handicapped in giving protection at night, additional dependence must be placed on passive measures supplemented by the fire of organic weapons of troops in position. (See pars. 421 and 633.)

  1. In the rear area, antiaircraft artillery cooperates with friendly aviation in protecting important establishments from air attack.

  2. The threat from troops transported by and landed from aircraft requires that special security measures be instituted against them. Responsibility for these measures extends down through all echelons of command, the measures adopted within each echelon being coordinated in such a way to provide a unified system over the entire danger area. In general, the security measures adopted are designed to gain early information, to attack incoming enemy transports by combat aviation and antiaircraft fire, to destroy parachute troops while in the act of landing or immediately afterward when they are most vulnerable, to obstruct all possible landing fields (airdromes, open fields, and straight stretches of level highway), and to isolate and destroy all landing forces by immediate attack before they can be resupplied and reinforced with supporting weapons. Defensive measures must not be reduced to routine; routine will assist the enemy in gaining surprise. (For details, see ch. 13 and FM 100-15.)


  3. Counterreconnaissance includes measures to screen a command from hostile observation. It is executed principally by aviation, antiaircraft artillery, cavalry, armored units, and security detachments. The commander coordinates the action of all of his counterreconnaissance agencies by assigning to each a mission in accord with its capabilities.

  4. Bombardment aviation contributes materially to counterreconnaissance by attacking hostile airdromes. Pursuit aviation, employed for counterreconnaissance on fronts where it is important to conceal our own activity from hostile


    air reconnaissance, attacks all hostile aviation. Since complete elimination of hostile air reconnaissance cannot be expected, where secrecy is desired, ground forces must conceal their movements and dispositions.

  1. Combat aviation in counterreconnaissance is supplemented by antiaircraft artillery and the weapons of other units. Subject to the desirability of maintaining secrecy, all hostile aviation within range is fired upon to prevent observation. Before the fire of antiaircraft weapons is resorted to, consideration must be given to the fact that such fire may disclose the importance of the area being screened.

  2. Units assigned counterreconnaissance as their principal mission seek to defeat or neutralize hostile reconnaissance forces. In the execution of this mission, they operate offensively, defensively, or by delaying action, resorting to all forms of combat when necessary.

    Offensive counterreconnaissance is most effectively executed by the defeat of the hostile reconnaissance forces. The activity of hostile patrols is most completely eliminated by the defeat of the stronger supporting detachments.

    Defensive counterreconnaissance is most effective when the screen can be established behind an obstacle which must be crossed by hostile reconnaissance forces. Elements are employed to obtain information, attack advanced enemy detachments, or obstruct their operations.

    When a broad front must be covered, it may be necessary to resort to delaying action to impede temporarily the operations of hostile reconnaissance forces.

    Aviation assists counterreconnaissance by attacking hostile aviation attempting to cross the zone of counterreconnaissance and by reporting hostile ground movements, especially the approach of highly mobile units.

  3. The counterreconnaissance screen may be either moving or stationary. A moving screen is applicable to situations where the movement of a force must be screened; a stationary screen is used to screen the dispositions or concentration of troops or prevent the enemy from reconnoitering an area. (See ch. 15.)



  1. The object of counterintelligence is to destroy the effectiveness of the enemy intelligence system. Counterintelligence measures available to a command include secrecy; discipline; concealment; tactical measures designed to deceive the enemy; restrictions on the preparation, transmission, and use of documents; signal communication security; precautions in the movements of troops and individuals; regulation of the activities of newspaper correspondents, photographers, radio news commentators, and visitors; censorship; counterespionage, and counterpropaganda. (See FM 30-25.)

  2. It is imperative that all members of the military service realize that thoughtless or talkative persons may become a menace to their country and to the lives of their comrades. Officers, enlisted men, and civilian employees must not discuss military instructions, plans, operations, movements, or the composition or location of troops in the presence of civilians or other unknown persons. In making preparations for operations, it frequently will be advisable to take special precautions to maintain secrecy. Secrecy precautions must not jeopardize the success of operations by withholding information necessary to the forces involved.

  3. All members of the military service should understand that if they are captured the enemy will make every effort to obtain information from them. They will be instructed to give correctly their name, rank, and serial number, and maintain absolute silence when asked any other questions. Any other information given may prejudice the success of operations and endanger the lives of their comrades.

  4. Troops should make maximum use of natural and artificial concealment. Natural concealment and cover should be supplemented by camouflage. Since photographs frequently disclose things not visible to an observer's unaided eye, commanders should prevent the making of trails, tracks, or other telltale marks in the vicinity of any work. In general, it is useless to attempt to camouflage a position where work has already been begun which the enemy has had an opportunity to observe and register.

    In general, troop movements in the combat zone should be


    made under cover of darkness and with restrictions on the use of lights. If the enemy possesses a powerful air force, a blackout system must be employed. Under favorable conditions, smoke can be placed over restricted areas for limited periods of time to conceal information of great importance.

  1. A commander who is ingenious and resourceful in the use of tactical stratagems and ruses often will find methods of deceiving or misleading the enemy and of concealing his own intentions.

    Feints, demonstrations, and simulated concentrations may be employed to mislead the enemy regarding the strength, time, or place of attack. The main attack may be accompanied or preceded by secondary attacks made in such a manner as to conceal the location of the main attack. A carefully screened withdrawal may be employed to deny the enemy the choice of the time and place of attack. Marches by day and return at night and the movement of empty truck columns have been employed to create the impression of great activity. Fake concentrations; simulated bivouacs, airdromes, and radio installations; dummy field fortifications, artillery positions, tanks, and airplanes; and many other such means have been successfully employed. It often is practicable to deceive the enemy regarding our plans and intentions by changing any routine procedure which may have come to his attention.

    The dissemination of false information designed to deceive or mislead the enemy as to our intentions, capabilities, morale, or dispositions, such as, for example, the deliberate loss of orders or prisoners always introduces an element of danger because our own plans and decisions are apt to be influenced by the assumption that the enemy has been deceived. Such measures may be adopted only by the theater commander or by his authority.

  2. Counterreconnaissance is employed on fronts where it is especially important to conceal the disposition of troops from hostile investigation.

  3. Precautions are taken in the safeguarding and transmission of secret, confidential, and restricted documents. All orders, pamphlets, maps, diagrams, publications, or manuals and similar matter, except messages, originating in the theater of operations are classified as restricted unless given a


    more restrictive classification. Military personnel in the front lines, on reconnaissance, or on missions over the enemy's lines, will not, under any circumstances, have in their possession any documents, except those absolutely necessary for the execution of their missions.

  1. Secrecy in the transmission of messages is of the utmost importance. Commanding officers are responsible for the maintenance of signal security within their commands. The signal intelligence service is responsible for the surveillance of friendly signal communication. The use of codes and ciphers is restricted to personnel specially trained in cryptography.

  2. Before leaving a camp, concentration area, rest area, bivouac, or any other assigned area in the theater of operation, troops will make a systematic search of the area to insure that no documents or other evidence of potential intelligence value to the enemy remain.

  3. The objects of censorship are to prevent information of military value from reaching the enemy, to insure that only accurate accounts of military activities are published or broadcast, and to maintain friendly relations with allied and neutral nations.


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