July-August - Air Defense Artillery School

Stereoscopic Viewer
By Colonel Maurice Morgan, Coast Artillery Corps
A recent issue of Tile J\lilitary Surgeoll contained an
article' by l\lajor Erwin E. Grossman, i\ledical Corps.
formerly stationed at Camp Hulen, Texas, covering the relationship
of the eye to antiaircraft gunnery. In connection
with the reproduction of certain portions of the article and
at the request of the Editor of the JOURNAL, these notes
have been prepared covering the trial use at Camp Hulen
of a locally designed depth perception viewer in relation to
automatic weapon fire.
Manv readers will be more or less familiar with numerous
method~, devices, and gadgets which have been used with
varying success in the attempt to obtain and apply automatic
weapon pointing corrections in firing at aerial targets. The
writer must plead guilty to some "gadgeteering" in past years
which contributed much of interest but little, I fear, of
practical value toward the solution of the two principal gunnery
requirements which have not yet in my opinion been
adequately met.
(a) Definite and certain knowledge as to the sense and
approximate amount of deviations.
(b) Ready means for applying an appropriate correction
in time for it to be of value.
Having observed the continued difficulty encountered by
range setters and others in attempting to sense "overs" and
"shorts" during the brief period required by the tracer to
traverse the presented area of a diaphanous £lag target and
the added uncertainty which accompanied the procedure
when "line" shots were for any reason not obtained, it was
decided to experiment with a home made adaptation of the
stereoscopic height finder, omitting the element of calibrated
range readings, in the effort to develop a means whereby
range sensing could be accomplished with increased certainty.
There was nothing original in the design and the materials
were "procured" locally. The instrument was designed
to extend stereoscopic limitations of normal unaided
vision by providing a bifocal separation of approximately
five feet instead of the normal pupillary diameter of sixtyfive
millimeters, in conjunction with six-power binoculars
issued to automatic weapon battalions. The viewer consisted
essentially of a rectangular box (5' x 10" x 10") mounted
on a metal tripod to permit tracking in azimuth and angular
height. Two pairs of front-silvered mirrors (one 7" x 7"
and one 5" x 5") were mounted inside the box so as to permit
of a double right angle reRection into the objective
ends of six-power binoculars which were fastened to the
exterior of the box by a clamp and screw in rear of apertures
fronting on the smaller (center) pair of mirrors. One of the
center mirrors was connected bv a threaded screw to an
exterior adjusting knob to pe~it limited rotation of the
mirror in azimuth and a separate but similar arrangement
was provided to enable rotation of the other center mirror
'Extracted in COAST ARTILLERY JOUR:-:AL. Mar-June. 1943. issue.
in a vertical plane. The adjusting knobs permitted settinD!
of the mirrors for targets of different ranges and were neces~
sary to prevent double images (lateral and vertical) which
would otherwise be present due to parallax and rough meth.
ods used in mirror mountings. In adjusting the viewer for
observation of A\V fire it was found most advantageous to
focus the binoculars for a distance of about 1000 yards
clamp them to the box and manipulate the azimuth and
vertical adjusting knobs until a suitable object at that
distance (1000 yards) produced a single, clear image
Further adjustment of either the binoculars or the mirrors of
the viewer was generally unnecessary for targets at usual\
40rnm operating ranges.
A private of the Training Center Record Section \\asI
given opportunity to accustom himself to tracking the £lag
target. He received the usual coaching in the recognition
of obscuration or silhouette applicable to the norma] "]ine
shot. In addition he was impressed with the basic pro-j
cedure required for attempted sensings on non-line shots,
i.e., to note if possible the comparative distance relationship
of target and tracer when both were most nearly in lineal
conjunction or (as some prefer to state) to note the relatire
juxtaposition of target and tracer at the instant when the
tracer appears to intersect the vertical plane containing the
target path.
After the foregoing preliminary instruction a test \\a5