Guns emplaced on permanent mounts or in static positions are generally used throughout the air defense system. The emplacements are usually well prepared, with living quarters for the crews. Calibers of these static guns range from the light 20-mm to the heavy 150-mm guns, most of the latter being permanently emplaced in readiness for both AA and coast defense roles. It is known that the light- and medium-caliber guns are also mounted on the tops of high building's and factories.

Figure 16.—German 88-mm gun in static position. (Note protection provided for gun crew.)

b. Use of Towers

Guns engaged in a static role are also emplaced in towers of various kinds. For example, in Berlin there are at least two concrete towers 250 feet square and over 100 feet high. Each of these has a "satellite" tower, a smaller rectangular structure about 350 yards distant. The larger towers each have four heavy AA guns, one being mounted on each corner; the smaller towers each have four light AA guns and what appears to be a radio-location instrument. It is believed that these towers are also used in the control system.

c. Use of Mobile Guns

Mobile guns include those on railway mounts. In some areas a proportion of the gun defenses are mobile so that guns and gun positions may be altered on short notice. In order to achieve the maximum effect, the Germans believe that the system of AA defense should be extremely flexible, and the active means of defense are therefore closely coordinated with the means for deception. Under this system, different positions can be taken by mobile units at different times. For example, if system "A" is used tonight, the mobile force will take position in area 1; if system "B" is selected, they will be installed in area 2, etc. These systems of antiaircraft defense are changed frequently in order to meet changes in the tactics of enemy aviation. The net result theoretically operates to produce confusion in the mind of any hostile aviator who might attempt to orient himself through locations of a series of gun positions based on past experience. Guns emplaced in these positions are nearly always countersunk to permit continuous firing throughout an air raid with maximum protection to the crews.

d. Use of Dummy Guns and Dummy Positions

In keeping with the practices of active deception mentioned in the previous paragraph, the Germans employ dummy gun positions and dummy guns. The latter are usually employed along probable lines of air approach, and it is known that dummy gun flashes have been used. Furthermore, mobile guns may rotate through the various dummy positions, thus precluding any safe conclusions, based on hostile air reconnaissance, as to the existence of a set system of dummy positions.

e. Disposition of AA Guns in Rear Areas

(1) General.—In heavily defended areas, heavy guns are disposed on the outskirts with special attention to the expected lines of approach. A certain number of positions will be in the area itself, and will be situated about 6,000 yards apart where the target is a large one. Light guns are concentrated at particularly vulnerable points, such as factories and docks. They are occasionally emplaced on lines of approach, such as canals, rivers, or arterial roads. For isolated vulnerable points, the disposition of defenses is a special problem which varies with the nature of the particular target. For example, airdromes generally have 12 or more heavy guns, none placed nearer than 2 miles, and 12 to 30 light guns, none located nearer to the perimeter than 500 yards.

(2) Heavy guns.—(a) Four-gun positions (fig. 17).—In the normal four-gun layout, the guns are sited roughly in a square of approximately 70 yards to a side. A fully equipped position has two command posts, which for convenience may be termed Command Post No. 1 and Command Post No. 2. Command Post No. 1 is usually situated about 100 yards to the side of the gun layout, and contains the Kommandogerät, which transmits data by cable to a junction box located in the center of the square, and thence to each of the four guns. Command Post No. 2 is located approximately in the center of the square, and normally contains the auxiliary predictor (director), with its separate height- and range-finder. Communication from the auxiliary predictor to each gun is by telephone. The fire is normally controlled from Command Post No. 1; in the event of destruction or failure of the Kommandogerät or the transmission system, fire is controlled from Command Post No. 2.

Depending on the terrain, 20-mm guns are normally located between the gun layout and Command Post No. 1 in order to provide protection against low-flying aircraft.

Figure 17.—4-gun layout.

In a great many cases, the normal four-gun layout has only one command post, either in the center or, more frequently, to the side. The provision of two command posts depends partly on the importance of the locality and partly on the availability of equipment.

It is interesting to observe that wherever the existence of radio-location fire control has been suspected or observed, the equipment has been found on sites with one command post to the side, and always in close proximity to the command post. Where this equipment is used, it is suspected that one set may furnish data for several nearby gun batteries.

(b) Six-gun positions.—Six-gun layouts fall into three main categories:—

(1) Those expanded from existing four-gun layouts by the addition of two emplacements, one on either side of the original square.

Figure 18. 6-gun layout for coastal defense.

(2) New layouts, consisting either of five guns sites roughly in the form of a circle, with the sixth gun in the center, or of all six guns in the form or a circle.

(3) Coastal layouts, consisting of four guns in a straight line facing the sea, with the remaining two guns in rear (fig. 18).

The command post on six-gun positions is almost invariably located outside the gun layout, except in the case of the coastal layouts, where it is usually located between the two landward emplacements.

(3) Light and medium guns.—A triangular layout of light and medium guns is common, but not invariable, with the guns anywhere from 75 to 150 yards apart. Guns are seldom deployed singly. In built-up areas, considerable use is made of light guns on specially constructed towers; they are also mounted on the roofs of buildings.

f. Fire-Control Methods

(1) With heavy guns.—The Germans use several types of fire-control methods with heavy AA guns. As has already been indicated, the data-computing director used by the Germans does not differ materially from that used by the U.S. Army, except for the fact that in the latest standard type of director the Germans incorporate the height- and range-finder and the predicting mechanism into one instrument. Since there are times when the target is not seen, or when for various reasons it may not be practicable to rely on fire directed at only one aerial target, the Germans use several methods of fire control, principally the following:

(a) With director where target is seen.—This is the normal method and is employed under suitable conditions by day, or in conjunction with searchlights by night. The use of mechanical fuze-setters permits the maintenance of a high rate of fire. Guns may fire singly, but in recent months a tendency towards salvo firing has been observed. At night, targets in searchlight "cones" are engaged by large gun densities, indicating a preference for this type of fire.

(b) With director where target is unseen.—This method may be used by day in overcast conditions, or by night in the absence of searchlight illumination. The use of this method presupposes some means, other than visual, of obtaining the basic elements of present azimuth, present angular height, and present slant range. The Germans are known to have experimented with and used searchlight sound locators for this purpose, fixing the location of the target in space by finding the intersection point of data received from two or more separate sound locators. Authentic reports indicate, however, that the Germans have not found the use of searchlight sound locators to be very satisfactory for this purpose. Since the Germans are known to have been employing radio-location instruments since 1940, it is quite certain that such instruments are now being used for obtaining the initial data.

(c) Predicted concentrations.—In this method a number of gun positions operate under a central control or "master station"; gun densities may include as many as 32 guns. Predicted salvos from individual positions have also been encountered. Unless irregular evasive action is taken by the hostile aircraft, both types of fire can be fairly accurately produced by taking a mean of plots of the plane's course.

(d) Fixed barrages.—This method was particularly used in the early part of the war. Controlled by a central operations room, the fire can be laid in almost any shape; screen, box, cylindrical, or in depth. This type of barrage is usually put up over a vulnerable point or just outside the bomb release line. At the present time it is used mostly at night or under conditions of bad visibility. Furthermore, the development of up-to-date instruments has made its use secondary.

(2) With light and medium guns.—(a) At visible targets.—By use of the several course and speed sights, AA fire from light and medium guns is opened With reasonable accuracy, and corrections are made by observation of tracers. The light or medium AA guns are highly maneuverable and can engage a target almost immediately as it comes in view and in range. These guns rely for effect on the high rate and volume of fire. For altitudes below 1,500 feet, they are exceedingly accurate. At very low levels, particularly from 0 to 50 feet, accuracy is considerably reduced, owing partly to the limitation of field of view with a consequent restricted time of engagement, and partly to the high angular velocity of the target in relation to the guns. By night the method of engagement of an illuminated target is similar to that used by day, with greater reliance placed on observation of tracer.

(b) At unseen targets.—Against unseen targets, light AA fire is nothing more than a deterrent, as the Germans have no instruments for "unseen" firing with light and medium guns. These guns are sometimes sited close to a heavy searchlight, probably for the purpose of obtaining early approximate data, as well as for the protection of the searchlight.

(c) Fixed or curtain barrages.—Fixed or curtain barrages are occasionally fired by the weapons by day or by night over small vulnerable points, at targets or along likely lines of approach.