THE COAST ARTILLERY JOURNAL - Air Defense Artillery

Spotting and Plotting for Antiaircraft Artillery
From the Aberdeen Tests
I. OBSERVATION OF BURSTS
1. Method of Measuring Deviations. a. The problem of measuring and
recording the position of the bursts of antiaircraft gun fire with respect to the
target is of primary importance. The first method used in our service provided
for measurements in range and in vertical deflectionby means of a grid held
by the observer in the towing plane. The observer was supposed to record his
observations on specially prepared cards. Lateral deviations were read by
observers on the ground. This system was hopeless. The aerial observer could
never obtain but a small percentage of the bursts, recording was very difficult
for him, and the synchronization of his results with those of the ground ob.
servers was impossible.
b. At Aberdeen during the antiaircraft tests a complete ground system
was installed. This year two methods of obtaining deviation of bursts from
the towed target were used; these were the camera method and the visual
method. Since these two systems used approximately the same base line and
the same orientation data, the deviations obtained by each could be compared.
The course of the target could be plotted and results from each system computed.
The two systemsprovided a check against each other, made certain that
a course would not be lost should one system fail for any reason to obtain
deviations, and permitted of a comparison as regards accuracy and the ability
of each system to observe under various conditions of visibility and dispersion.
For further data on comparison of visual and camera system see paragraph
14 of the Final Report, Antiaircraft Firings and Tests, Aberdeen Proving
Ground, Maryland, 1928.
2. The Camera Method. a. The apparatus used in this method consists
of two Bell and Howell B motion picture cameras, each mounted on the modi.
fied base of an azimuth instrument, M-1918. To the trunnion carrying the
camera is attached an elbow telescope M-2 whose line of collimation can be
made exactly parallel to that of the camera. Each camera is normally operated
by a small motor and the two camera units are synchronized by means of a
relay circuit closed approximately every second by means of a clockwork. A
small electric lamp in the relay circuit marks the film of each camera at the
same time as often as the relay circuit closes. One projector and the necessary
developing and drying equipment are necessary in the laboratory. Specially
prepared grid screens laid off to the proper scale for projecting the film are
also required.
b. In nse a camera unit is set up at each end of a base line whose length
and azimuth is accurately known and the necessary telephone and synchronizing