A report on German signals between air and ground forces in WWII, from Tactical and Technical Trends, No. 24, May 6, 1943. [DISCLAIMER: The following text is taken from the U.S. War Department publication Tactical and Technical Trends. As with all wartime intelligence information, data may be incomplete or inaccurate. No attempt has been made to update or correct the text. Any views or opinions expressed do not necessarily represent those of the website.]

GERMAN VISUAL COMMUNICATION BETWEEN AIRCRAFT AND GROUND TROOPS Modern warfare puts a heavy premium on successful coordination of all of the various arms. For that reason, comprehensive and flexible methods of communication must be devised. Liaison between air and ground forces presents special problems, and a German document gives the following outline of methods used to meet some of the difficulties. *          *          * a. Cooperation Cooperation between army and air force is to be arranged through the respective headquarters, prior to each action. The appropriate headquarters of both branches of the service are also responsible for keeping themselves mutually and speedily informed of all movements in their battle area, both on the ground and in the air. b. Method of Recognition Detailed knowledge of friendly aircraft types, pre-arranged signals, and the air situation, distributed down to companies, will facilitate early recognition by the troops. When the air crews possess knowledge of the situation on the ground, of the general conduct of ground troops in battle, and of the signals arranged for, this will enable the pilot to distinguish quickly between friendly ground troops and those of the enemy. Recognition signals can only be seen if they are given at the right moment and in the correct position. Ground troops must give their signals early and in a position easily observed from the air. Aircraft must be able to observe the signals well before arriving over the position. Aircraft must NOT give their signals too soon, as ground troops are often hindered in their observation by cover. Only when the ground is flat and when aircraft are flying low should early signals be given. Flying unnecessarily low over friendly troops is to be avoided, as recognition by the troops is made difficult through the sudden appearance of planes. c. Signals (1) Recognition of Friendly Ground Forces Means which are employed during daytime to indicate friendly troops are as follows: (a) Orange-colored smoke signal (b) Yellow panels (only for the front line) (c) Swastika flags (d) Any other signals which assist recognition. The orange-colored smoke is the signal most easily recognized from the air. It means "friendly troops; we are here." It is the chief recognition signal for all ground troops. The yellow panels are in general recognizable from medium heights if they are laid out in an advantageous position. Numerous yellow panels side by side facilitate recognition. Yellow panels mean "here is our own front line." They are only to be used for this signal and NOT in any other situation, in order to ensure that the front line is clearly indicated. The aircraft can draw its own conclusions as to the battle situation. When friendly troops advance, the yellow panels must NOT be left behind. In addition, the orange smoke signal is to be used as extensively as possible. Swastika flags can hardly be seen from great heights, and only with difficulty from medium heights. They mean "friendly troops; we are here." They are generally used in rear positions, particularly by columns, etc., but can be used in the front line if yellow panels are NOT available or if NO particular value is attached to the distinct recognition of the front line. As swastika flags alone are NOT generally sufficient, the additional use of the orange smoke signal is advisable. Any other signals may be used by the troops, if the usual recognition signals are NOT available. Improvised signals can include: laying out of swastika flags on snow or light background, and waving of steel helmets and handkerchiefs, etc. These signals are, however, only an improvisation - they do not afford any guarantee that the ground troops will be recognized. (2) Recognition of Friendly Aircraft Means by which aircraft can be recognized are: (a) Type of aircraft and national marking (b) Special painting (or camouflage) (c) Recognition light signals (d) Any other improvised signals. The special type of painting is usually ordered to be uniform throughout the entire air force for a fairly long period; for instance, yellow wing tips and a ring round the fuselage. The recognition signal is changed continually and must be made known to the commands, etc. Improvised signals can include: dipping the nose and tail of plane up and down, and repeated deceleration and acceleration, etc. These signals are only improvised if others are NOT available and they afford NO guarantee that the aircraft will be recognized. d. Means for Night Indication of Friendly Troops or Friendly Aircraft (1) For Ground Troops Flashes and light signals of all descriptions Special light signals ordered from time to time (for short-distance, night reconnaissance aircraft (2) For Aircraft (a) Recognition signals and lights (b) Fixed lights (c) Flashes with searchlight on aircraft. The above signals are continually changed and must be made known down to companies, etc. e. Use of Recognition Signals (1) Recognition signals by day must be given by ground troops: (a) When called for by signal from air units (b) If an attack is threatened by friendly aircraft. The order to signal is given by the company commander; by aircraft, when fired on by friendly troops. (2) Recognition signals by day can further be given: (a) By ground troops, if they consider it necessary to identify themselves to the aircraft, without being called upon to do so - particularly if the position justifies the assumption that the aircraft has omitted to call for signals. (b) By aircraft, when suddenly emerging from clouds over own territory, or as a request to ground troops to give their signals. (3) Recognition signals by night must be given by ground troops, when called for by friendly aircraft; also, when the position justifies the anticipation of a bombing attack by friendly aircraft. The order to signal is given by the company commander; by aircraft, if in danger of attack from friendly troops. (4) Night signals can further be given by aircraft: (a) To ascertain own territory, if bearings are lost (b) If it is known or believed that the aircraft are crossing the front (generally this is usual only on the return flight) (c) As a request to own troops to give their signals (d) In the area of an airfield, shortly before landing. (5) In addition to these general instructions, special signals and their use in certain cases can be arranged by cooperation between flying units and ground troops. A safety line can be arranged for a fixed period between the respective air and army headquarters. Operations in rear of this safety line can only take place if recognition of the front line is perfectly clear (with good visibility, at about 6,500 to 10,000 feet), or if the target ascertained through tactical reconnaissance immediately before the attack is free of our own troops. Night attacks on the near side of this safety line must NOT be undertaken. The safety line should give a safety zone of at least 1,000 feet. Air force headquarters must be informed in cases where friendly troops may be in possession of captured enemy material. f. Secrecy of Recognition Signals The enemy may be expected to cony German signals and every soldier must NOT ONLY realize the necessity of secrecy but must also report immediately any cases where the enemy are using our recognition signals. g. Ground Panels A time may be laid down in orders for making signals. The aircraft may call for signals by flare. The troops may put out signals on their own accord. The order for making these signals will NOT be given by officers below the status of company commanders, etc. These panels will be laid out so that they are always read when looking towards the front. They must be laid out in good time so that the aircraft does NOT have to circle over the battle area. They may only be lifted when the aircraft is out of sight. The signs must be laid out on a background against which they can be clearly picked out from the air. Where possible they must be laid out in open ground, as aircraft usually observe while approaching and NOT when directly over the position. Thus, bushes, trees, etc., may prevent the signs being seen obliquely. h. Messages by Use of Very Lights. etc. (1) By Aircraft (a) White Very lights - a demand to the troops to make recognition signals (b) Green Very lights - the observer is going to drop a message "Lay out message-dropping cross or make some other indication of dropping place" (c) Red smoke signal or red Very light - "Beware enemy antitank weapons, antitank gun, artillery, obstacles" (d) Blue or Violet smoke signal - "Beware enemy tanks." White and green Very lights will be fired obliquely downwards over the battle area, or approaching it. Smoke signals will be thrown by hand from the aircraft in the direction of the enemy target which has been spotted. Their direction of flight and position will indicate the approximate target. Improvised methods can be used, such as: the aircraft circles over the battle area several times, or flies low over the troops several times, in order to attract their attention (this is a demand for the troops to display recognition signals); diving on the enemy area in a certain direction, firing in bursts to indicate the observed target to the troops; dropping of short written message to supplement the information (messages will be dropped in message boxes which emit a yellow smoke while dropping, and on the ground). If this is NOT possible they will be dropped in message bags with a red and white streamer. (2) By Troops When the normal system of ground panels is NOT used, short messages can be transmitted by the use of Very lights. These signals and any other improvised methods MUST be prearranged. These last two signs are to be laid out with the big vertical strip pointing to the enemy, and the cross strips nearest the enemy.

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