A report on German signals between aircraft and ground forces based on captured German documents, from the Intelligence Bulletin, March 1943. [Editor's Note: The following article is wartime information on enemy tactics and equipment published for Allied soldiers. In most cases, more accurate data is available in postwar publications.]

VISUAL SIGNALS BETWEEN AIR AND GROUND FORCES 1. INTRODUCTION The German system of visual communication between ground troops and aircraft is well developed. Extracts from a German document explaining the system are reprinted below. It must he remembered, however, that the Germans take the precaution of changing their signals as often as possible. Perhaps the chief value of these extracts is that they illustrate basic methods of air-ground visual signaling and the importance attached to them by the Germans. 2. COORDINATION Coordination between Army and Air Force is to be arranged through the respective headquarters prior to each action. The appropriate headquarters of these two branches of the service are also responsible for keeping themselves mutually and speedily informed regarding all movements in their battle area, both on the ground and in the air. To speed up recognition, ground troops should possess detailed knowledge of our own aircraft types, of the prearranged signals, and of the air situation. This information should be distributed down to companies, whose commanders may give orders to signal. If air crews are aware of the situation on the ground, of the general conduct of ground troops in battle, and of the prearranged signals, gunners will be able to distinguish more quickly between enemy troops and friendly troops. Ground troops must give their signals early and in a position easily observed from the air. Aircraft must be able to see the signals before arriving over the position. Aircraft must not give their signals too soon, inasmuch as cover often interferes with observation by ground troops. Only when the ground is flat, and when the aircraft are flying low, may early signals be given. Since recognition by ground troops is difficult when planes appear overhead too suddenly, unnecessarily low flying over our own troops is to be avoided. 3. DAY SIGNALS USED BY GROUND TROOPS In the daytime, ground troops must give recognition signals when air units call for them by giving their own recognition signals, or if friendly aircraft threaten to attack. Also, ground troops may give daytime recognition signals without being called upon to do so if they consider it necessary to identify themselves to friendly aircraft—especially where terrain features tend to obscure ground troops from air observation. a. Orange Smoke Orange-colored smoke is the signal most easily recognized from the air. It means, "own troops are here." It is the chief recognition signal for all ground troops. b. Identification Panels Identification panels will be laid out so that they may be read from aircraft flying toward the front. They must be arranged in good time, and on a background against which they can be picked out clearly from the air, so that the aircraft will not be obliged to circle over the battle area. The panels should be spread on open ground, wherever possible, since aircraft usually observe while approaching, and not when directly over a position. Trees, bushes, and other objects may prevent aircraft from seeing the signals obliquely. Every effort must be made to make the signals as large as possible. Panels may be lifted only when the aircraft are out of sight. Yellow cloths mean "here is our own front line." They are to be used only for this message, so that the front line will always be clearly indicated. The aircraft can draw its own conclusions as to the battle situation. In general, yellow is easily recognizable from a moderate height; a number of yellow cloths spread out side by side will make identification easier. When our own troops advance, the yellow cloths must not be left behind. In addition, the orange smoke signal is to be used as extensively as possible. c. Swastika Flags Swastika flags can scarcely be identified at all from great heights, and only with difficulty from moderate heights. They mean "own troops are here." As a rule, they are used in rear positions, but may be used in the front line if yellow cloths are not available or if no particular value is attached to a distinct recognition of the front line as such. Since swastika flags alone are generally not sufficient for identification purposes, it is advisable to use the additional signal of orange smoke. d. Improvised Signals If the usual recognition signals are not available, troops may improvise signals, such as the waving of steel helmets, handkerchiefs, and so on. However, these signals afford no guarantee that the ground troops will be recognized. 4. DAY SIGNALS USED BY AIRCRAFT In the daytime, aircraft must give recognition signals when fired on by friendly troops. Daytime signals may also be given by aircraft which suddenly emerge from clouds over friendly territory, or which wish to request signals from ground troops. Ground troops will generally identify friendly aircraft by noting the type of plane, the national marking, or special painting. When security permits, messages will be dropped in message boxes which emit a yellow smoke while dropping and after reaching the ground. If these boxes are not available, messages will be dropped in message bags, to which a red-and-white streamer is attached. Aircraft may improvise such signals as the dipping up and down of the nose and tail of a plane, wing dipping, or repeated spurts of the motor ("jackrabbiting"). 5. NIGHT SIGNALS USED BY GROUND TROOPS At night, ground troops must give recognition signals when these are requested by our own aircraft, and when the situation warrants anticipating a bombing attack by our own aircraft. Ground troops use light signals of all types, making extensive use of Very lights. Codes are changed continually, of course, and are made known down to companies. 6. NIGHT SIGNALS USED BY AIRCRAFT Aircraft must give night signals when there is danger of attack by friendly troops. Further, aircraft are permitted to signal at night if they have lost their bearings and wish to know whether they are flying over friendly territory; if they know, or believe, that they are crossing the front on a return flight; when they wish to request friendly troops to give signals; and when they are about to land at an airdrome. Aircraft must continually change the meanings of their fixed light signals and flashed searchlight signals. 7. USE OF VERY LIGHTS The Germans use white, green, and red Very lights. At the time the above instructions were published, German aircraft used white Very lights to request ground troops to give recognition signals: green, when a plane was about to drop a message and wished ground troops to indicate where they preferred to have it dropped; and red, to convey the message "Beware of enemy antitank weapons." Red smoke signals also were used to convey this last message, while blue or violet smoke signals were used to indicate the presence of enemy tanks.

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