Tag Archive for 'director'

Fire Control Equipment for 75 mm Model 88 (1928) A.A. Gun

Fire Control Equipment for 75 mm Model 88 (1928) A.A. Gun

These instruments are used with the Mobile Field Antiaircraft Gun described on page 110. The method used to predict the future position of a moving target in space differs from both the angular rate of travel and the linear speed methods, although based on the latter. Antiaircraft installations captured before the middle of 1944 showed very little use of computing directors and remote control systems. The system described herein is apparently all that was available.

The following instruments and computing mechanisms are employed in the system as off-carriage components:

a. Two-meter-base height and range finder.

b. Speed and course angle calculator.

c. Charge (propelling) temperature and wind corrector scale.

d. Spotting binoculars.

The data computed with the off-carriage components are transmitted orally to the gun where they are manually registered in the on-carriage fire control instruments. The on-carriage components consist of the following:

a. Elevation computing apparatus.

b. Azimuth computing apparatus.

c. Auxiliary elevation and lead corrector disc.

d. Fuze setter.

The accompanying illustrations show five of the significant components.

Japanese: p. 185 (April 1, 1945)

Antiaircraft Director, Model 2

This appears to be the latest model of mechanical antiaircraft director made by the Japanese. It has data receivers (selsyns) for azimuth, angle of site, and slant range, probably provided for use with radar equipment. Primary input data may also be obtained by optical tracking by means of telescopes attached to the director and a height finder.

Computation is based on angular rates. The transmitted data is future azimuth, future quadrant elevation, and future fuze. Data is transmitted to each weapon by means of selsyn motors and applied to the weapon by means of a match pointer system resembling that used with the American 90 mm, M1 antiaircraft fire control equipment. It is believed that this instrument is capable of furnishing data for three weapons. It is assumed the azimuth receiver will work with both the 8 cm and the 12 cm Japanese antiaircraft guns.

As compared with th her modern directors, it is felt that this instrument is deficient in both design and construction. An angular rate computer is considered too inaccurate for anything other than small or medium caliber automatic tracer controlled antiaircraft fire. Human error is permitted through the curve-following method of introducing time of flight, superelevation, and converting slant range into altitude. A great deal of backlash exists in various gear trains and in the mechanical linkage of the multipliers.


Limits as indicated by drums and dials
   Slant range (dial calibration)       40,000 meters
   Slant range (limit of movement w/ alt. converter) 19,000 meters
   Horizontal range 12,500 meters
   Altitude 9,000 meters
   Quadrant elevation -10° to + 90°
   Fuze 35 seconds
   Dead fuze time 10 seconds
   Wind velocity 20 meters/sec.
   Azimuth No limit
   Angular rate Undetermined
   Electrical data
      Cycles 50 or 60
      Volts 50 or 60
   Weapon with which used 120 mm, 45 cals. A.A. gun and 80 mm, 40 cals. A.A. gun.
   Height 44 1/4 ins.
   Length 34 1/2 ins.
   Date of manufacture Showa 18 (1943)
Weapon data obtained from drums
   Fuze types (120 mm gun) M88 (1928), M89 (1929), M91 (1931)
   Muzzle velocity 825 meters/sec.
   Fuze types (80 mm gun) M89 (1929), 5th year type (1930)
Muzzle velocity 670 meters/sec.

Japanese: p. 176 (March 1, 1945)

Antiaircraft Director

Antiaircraft Director (Japanese, WWII)

This director (possibly referred to by the Japanese as Model 97) is a plan prediction type of computer. It is probably used with the Japanese Model 88 (1928) 75 mm antiaircraft gun.

Standard ballistics are obtained from cams; approximations and spot corrections take care of wind effects, muzzle velocity, and air density variations. The director is provided with telescopes, and with electric data receivers for azimuth and angular height, and for altitude or horizontal range.

The director imposes significant limits on altitude and horizontal component rates. The maximum altitude rate is +/- 179 miles per hour. The maximum horizontal component rates are 335 miles per hour. It is not known whether it is Japanese practice to orientate their directors with respect to true North; but if that is the case, targets flying in the cardinal directions with ground speeds in excess of 335 miles per hour would be beyond the capability of this director. Such ground speeds, when aided by wind, may be feasible. It should be noted that the director is capable of handling greater speeds if the target does not fly parallel to one of the principal coordinate axes.

Optical tracking is provided on the director proper. An electrical data transmission system provides for the use of an external tracker such as a radar unit.


Time of flight         30 secs. max.
Present altitude         0 to 7,655 yds.
Future altitude         -820 to 8,475 yds.
Present horizontal range         0 to 10,936 yds.
Future horizontal range         0 to 10,936 yds.
N-S and E-W rates         +/- 164 yds./sec.
Altitude rate         +/- 87 yds./sec.
Lateral deection         +/- 800 mils.
Horizontal range prediction         +/- 4,101 yds.
Altitude prediction         +/- 820 yds.

Japanese: p. 175 (March 1, 1945)

Kommando-Gerät 36: Antiaircraft Director

Kommando-Gerät 36: Antiaircraft Director

The Kommando-Gerät 36 is a goniographic director, thus differing from directors which operate on plan prediction or angular travel methods. The present instrument measures target course and speed and solves the problem by setting up to scale in ground plan the various distances involved. Ballistic data are obtained from graphical drums; varying heights are accepted, and corrections can be applied for wind, drift, displacement, dead time, and variations in muzzle velocity.

The instrument which has a built-in range finder is large and heavy and has a 4-wheeled traveling carriage for mobile use. A crew of thirteen men is required to operate it.

Readings must be called out to the appropriate operator on the director. Information is passed from one operator to another by voice and via a telephone system.

The instrument is manufactured by Zeiss and displays excellent workmanship. This director, however, has been criticized by fire control experts for poor coordination of basic design and for the excessive number of men needed to operate it.

German: p. 175

Kommando-Gerät 40: Antiaircraft Director

The Kommando-Gerät 40 is a director used principally for major caliber weapons such as the 8.8 cm and 10.5 cm antiaircraft guns. However, by installing the proper ballistic cams, it may be used with any type of gun.

The director is operated by five men. Two are required to track in azimuth and elevation; a third sets in slant range by means of a 4-meter base stereo range finder mounted on the director; the fourth man sets in horizontal angle of approach; and the fifth man operates various switches. Data are transmitted to the guns for reception by a signal-light manual follow-up system. A trailer equipped with devices for lifting the director is used for transport.

The Kommando-Gerät 40 computes continuously Case III data (for invisible targets) by a target speed and angle of approach method, and can handle diving and curving target courses. The time from initial pickup to first round is estimated to be 20 or 30 seconds. When shifting to a new target in the vicinity of the target previously tracked and flying an approximately parallel course, as little as 10 seconds may be required.

A change in course which requires a change in operating procedure upsets firing data for only a few seconds. In principle, the director will predict correctly for a target flying at constant speed with a constant rate of change of altitude and constant curvature. The stability is not affected by gradual changes in course.

After an abrupt change in speed, altitude rate, or course azimuth, about 10 to 15 seconds are required to evaluate the new course.


Azimuth       No limit
Elevation -1.5° to 90.5°
Slant range 1,200 to 18,000 m
Present horizontal range 570 to 14,500 m
Future horizontal range 570 to 14,500 m
Future altitude -500 to 12,000 m
Present altitude 0 to 12,000 m
Ground speed of target 0 to 300 m/s
Vertical speed of target 0 to 200 m/s
Horizontal travel during time of flight 0 to 6,000 m
Lateral deflection +/- 1,065 mils
Course azimuth correction +/- 1,600 mils
Altitude prediction +/- 3,000 m
Maximum tracking rates
     Azimuth +/- 130 mils/sec.
     Slewing +/- 700 mils/sec.
     Elevation +/- 105 mils/sec.
     Time of flight 0 to 30 sec.
     Horizontal parallax 500 m
     Vertical parallax +/- 210 m
     Fuze dead time 0 to 10 sec.
     Wind velocity 0 to 28 m/s
     Muzzle velocity 24 numbers (Gebrauchsstufe)
     dØ +/- 60/16°
     dA +/- 70 mils
     dF due to dead time +/- 5 secs.
     dF due to MV and wind +/- 5 secs.

German: p. 176