There is no indication that a director of any type is ordinarily used with the light and medium Flak guns, the Germans apparently having decided that the development of the Flak sights already described is more profitable and practicable than the development of directors. For use with heavy guns. the German development of fire-control apparatus is strikingly similar to our own. They have an older, angular-speed director which is used for auxiliary purposes, but the latest and most commonly used instrument operates on the linear-speed method, using present azimuth, present angular height, and present slant range as basic elements.

b. Equipment

(1) Kommandogerät (stereoscopic fire director) (figs. 11 and 12).—(a) Description.—This fire-control instrument combines into one instrument a 4-meter-base Zeiss stereoscopic height- and range-finder, and a director. Two types are known: the No. 36, employed with the 8.8-cm Flak gun, and the No. 40, employed with the 10.5-cm Flak gun. The principles and method of operation of the No. 40 are not known, but they are probably similar to those of the No. 36, details of which follow.

(b) Method of operation.—The stages in the production of the firing data in the No. 36 are as follows:

(1) The height- and range-finder furnishes present azimuth, angle of sight, and slant range to the target, all of which may be termed initial data.

(2) The rate of change, obtained by continuously feeding this data into the predictor, provides the horizontal ground speed and the course angle of the target, which may be termed intermediate data.

Figure 11.—Kommandogerät in traveling position. (Note that the range-finder is carried separately.)

(3) The combination of initial and intermediate data provides the vertical and lateral defection and range correction to determine the future position. From this combination, the gun data is obtained by mechanical computation within the predictor.

(c) Transmission of data to guns.—The gun data thus obtained (in terms of firing azimuth, quadrant elevation, and fuze) are normally transmitted electrically to the guns, in the following manner: each of the three receiver dials at the gun (i.e., for firing azimuth, quadrant elevation, and fuze) is provided with three mechanical pointers pivoted at the center of the dial. There are three concentric circles on the dial, each with 10 holes numbered from 0 to 9, each hole being fitted with an electric bulb. The outer circle represents units; the center, tens; and the inner, hundreds. The appropriate bulbs light up in accordance with the data transmitted from the Kommandogerät. The actual value of the reading is different for each dial, the unit (i.e., on the outer circle) in each instance having the following values:

Figure 12.—Kommandogerät ready for use.

These figures provide a measure of the limits of accuracy obtained in transmission. The two gun-layers and the fuze-setter bring their mechanical data pointers into coincidence (covering the illuminated bulbs with the transparent celluloid ends of the pointers) by manually actuating azimuth and elevation handwheels on the guns, and the fuze-setting handwheel on the machine fuze-setter.

(2) Kommandohilfsgerät (auxiliary fire director).—This instrument is used for auxiliary purposes, and operates on the principle of calculation of the rates of change of angular velocity. A separate 4-meter-base stereoscopic height- and range-finder provides the present slant range to the target, and this data is passed orally to the director. By following the target continuously for azimuth and elevation, and by setting in range continuously, the rates of change of azimuth, elevation, and slant range are obtained. These, multiplied by time of flight, give the lateral and vertical deflections and a correction for range. These corrections, applied to the present data, provide future data which are corrected for abnormal ballistic conditions, dead time, and drift, and which are then passed to the guns as gun azimuth, quadrant elevation, and fuze. Data in this case are transmitted to the guns by telephone, no electrical transmission being provided.

(3) Telescopic sight for 88-mm gun.—The 8.8-cm gun is fitted with a telescopic sight primarily for the engagement of ground targets; the latest type is the telescopic sight 20-E (ZF 20-E). It weighs about 10 pounds and is a monocular type with a magnification of four and a field view of 17.5 degrees. The reticle is made with two cross lines interrupted at the center to form a laying mark, an arrangement which is usual in German instruments. There is a range drum graduated in hundreds from 0 to 9,400 meters, and a super-elevation drum with graduations of 1/16 of a degree, from 0° to 12°. There are also lateral- and vertical-deflection drums.

For AT use, the lateral- and vertical-deflection drums are set to zero. Range is set on the range drum, thereby automatically applying the necessary super-elevation. Corrections from observation of fire are applied to deflection drums as required.

An older type of instrument, the 2F 20, may be fitted. This has the same particulars, but no range drum; superelevation must be found from a range table and applied.

(4) Radio-location equipment.—It is known that German radio-location equipment for fire-control data is being produced on a high priority, and there is no doubt that this will constitute a most important line of future development. This activity is taking place parallel to the development of radio-detection equipment for warning against hostile aircraft. Aerial observers flying over gun positions in Germany and the gun-defended portions of occupied European countries have reported seeing instruments, identified as German radio-location instruments, in close proximity to gun positions. This would indicate that these radio-location instruments are being used with gun batteries, probably as a means of furnishing early basic data to the directors. Another possible use of these instruments is to furnish early information for calculation of data for barrage and deterrent fire.