A U.S. intelligence report on a WWII Japanese range and height finder, from Tactical and Technical Trends, No. 39, December 2, 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.]

JAPANESE HEIGHT FINDER The Japanese height finder is a sell-contained stereoscopic optical instrument used to measure both range and height on the principles of triangulation. It is dependent upon magnification and base length, the two basic conditions which serve to increase the stereoscopic sense of the observer. The greater the base length of the instrument and the greater the magnification, the greater amount of depth perception will be attained. This enables the observer to read with greater accuracy the distance to targets of extreme range or height. a. General The Japanese instrument has a base length of 7 feet 2 1/2 inches and can operate on only one range of magnification -- 20 power with a field of 2° 15'. Its total weight is about 500 pounds and it disassembles into three major units: the tripod, cradle and tube. These units are packed separately in steel containers for transportation. The Japanese instrument has only an outer tube and optical bar. In adjusting its measuring wedges, the Japanese height finder depends solely on external targets of known ranges or altitudes. However, it has an adjusting lathe of such construction and dimensions that when it is set about 50 yards from the instrument it can be used as an infinity target. At night this lathe is rendered useless so that it is necessary to adjust the height finder on a visible astronomical body such as the moon or a star. These bodies being at an infinite distance the measuring wedges are adjusted at their infinity setting. b. The Wedges There are two rotating and one sliding measuring-wedges, and a mechanism for concerting the wedge to read either range or height during operation. The correction wedge assembly is machined out of brass. It employs a system of stop rings to control complete movement of the glass wedge. c. The Optics The main optics of the Japanese height finder are extremely small in diameter so that the field of view is greatly decreased and the light transmission reduced. However, the instrument contains all the optics usually found in stereoscopic instruments, namely: 2 end windows, 2 end reflecting units, 2 objective lenses, 2 erecting systems, 2 ocular prisms, 2 reticles, 2 eye lenses, 2 field lenses, 2 rhomboid prisms, ray filters, height if image plate, correction wedge and the measuring wedge assembly. The optical bar, which contains the main optics, is made of a beautifully finished stainless steel. The adjustments of the optics are difficult because of their undesirable position in the optical bar. In many instances it is necessary to completely disassemble the instrument and remove the bar in order to make the necessary adjustments for satisfactory operation. There is a simplified method of drying out the optics in the tube. There are two plugs on either end of the tube through which dry air can be forced periodically but not during actual operation. The optics are of excellent quality but are believed to be of German manufacture. d. Operation The Japanese method of tracking a target makes it extremely difficult for the observer to get stereo-contact with the target. They have only one man tracking in azimuth and elevation and he must operate both handwheels for azimuth and elevation sitnultaneously observing through a simple metal open sight. The handwheels are both located to the right of the operator and are only a few inches apart. A small wooden box, used as a container for several batteries, is mounted on the left side of the cradle. These batteries furnish the only means of illumination for adjustment and operation of the instrument. The Japanese height finder has absolutely no electrical connections whatsoever with other instruments in the battery and the information found on the range drum is either telephoned or signaled in some other manner. The Japanese range drum is graduated from 400 to 20,000 meters. However, the Japanese use the mil scale for orienting their instruments. A circular mil scale is located directly below the tube in the center of the cradle, secured with two small screws. These screws can be loosened and the scale slipped until the desired reading is found. In the center of this scale is a large handwheel connected to the slip clutch plates which must be loosened through the action of the handwheel in order to slow the instrument; it must then be retightened to continue operation....

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