COAST ARTILLERY, JOURNAL - Air Defense Artillery

MORTAR FIRE CONTROL
Remark by the Coast Artillery Board:
3. c. The Coast Artillery Board concurs in the opInIOn that inter.
polation on the range-elevation board and the deflection board should be
accomplished by a permanent adjustable device rather than by means of
proportional dividers, as now prescribed. Devices similar to the interpolator
on the range percentage corrector are under test by the Coast Artillery
Board; and it is believed that the use of these devices will result in a saving
of time in the plotting room.
Extract from report of critique:
3. d. It appeared to be difficult to instruct a mall to operate the timeelevation
spiral rapidly. This was possibly due to the fact that the scale of
the spiral was too small. Thc operation of the time.azimuth check, the chart
of which was a straight line, was relatively easy. It is possible that a
straight-line, time-elevation check chart could be devised that would require
less training for its operation and at the same time include the equally
spaced range scale feature, probably one' zone on each horizontal line.
Remark by the Coast Artillery Board:
3. d. It is believed that a time-elevation spiral built to the proper SC:lle
will work satisfactorily. The difficulty with the spiral in question was doubtless
due to the fact that the print used was too small a reduction. The
time.el~vation spiral and time-azimuth board do permit of extrapolation in
case of a failure of communications between plotting room and emplace.
ment. These devices will probably be replaced by the plotting room interpolators
if the tests of the latter prove successful.
Extract from report of critique:
3. e. There was no method prescribed for interpolating d.lta for the
2-bell predicted point for the B. C. instrument. The following system was
worked out and gave very satisfactory results:
At' about the time of the three bells, the observer at the B. C. instrument
rec'eived the' data for the predicted point thirty: seconds in advance; he set
that data, noting how many turns of the handwheel it required. He then
turned the hand wheel back halfway, measuring the distance by the number
of turns. This gave an approximate setting for the 15-second interval,
which proved to he sufficiently accurate.
Remark by the Coast Artillery Board:
3. e. The scheme for interpolating data for the 2.hell predicted point i~
ingenious and very simple. The Coast Artillery Board is in favor, however, of
discontinuing the use of the predicted point, as stated above.
Extract' from report of critique:
3. f. During the iipng of fifteen shots in the maneuvers, held April 1 to
10, 1925; elevations "'ere set by the elevation scale and were not checked by
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