COAST ARTILLERY, JOURNAL - Air Defense Artillery

506 THECOASTARTILLERYJOURNAL
mining the travel in yards to the setforward point from the last plotted
observation. The last method of prediction was used at all practices
and was satisfactory. The Stephens Predictor, Coast Artillery Board
Project No. 419, has been developed since and is believed superior to
the methods used in the test.
c. Range Correction Board.-Both the Range Correction Board,
Model E, 1923, and the Pratt Range Board, Model 1905, have been
used; the former, modified as described in COASTARTILLERYJOURNAL
for March, 1926, was entirely satisfactory. Percentage curves were
used on the charts and operation was as indicated in T. R. 435-22l.
(See COASTARTILLERYJOURNALfor March, 1926.)
d. A standard wind component indicator was used in the test.
e. Range Percentage Corrector.-A range-elevation board is a
necessary adjunct to the fire control system of any mortar battery.
The most suitable range-elevation board known to the Coast Artillery
Board is the range percentage corrector described in T. R. 435-22l.
During the early part of the test proportional dividers were used for
interpolation. Later the range percentage corrector was provided with
an interpolating device.
f. Deflection Boara.-Two types of deflection boards have been
used in the tests:
(1) The deflection board for mortars, Model of 1906, with a new
lateral wind and drift chart substituted for the De Carre drift chart.
Various means of interp?lating were tried but no satisfactory method
was found. Due to the fact that when the azimuth cylinder is turned
one notch it is necessary to move the carriage to the extreme right or
left and the old azimuth reading is lost, it appears improbable that
a satisfactory method of interpolating on this board will be found. A
separate interpolating device with a continuous azimuth take was tried.
This was unsatisfactory because of the time required for the various
operations.
(2) The Coast Artillery Board Universal Deflection Board with
interpolator. (See COASTARTILLERYJOl::RNAL for May, 1925.) During
the test this deyice was modified slightly but there was no change made
in the principle of the board or in its operation. In its improvised
form the 1}niversal Deflection Board is subject to inaccuracies which
it is believed will not exist in an arsenal constructed device. An arsenal
constructed board is very desirable not only because of increased
accuracy but because of increased speed in operation. Since the corrected
azimuth can not be determined until after the corrected elevation
is found, the corrected azi_muthis usually late in getting to the pits and
is the most frequent cause of relays. Furthermore, there is difficulty in