THE COAST ARTILLERY JOURNAL - Air Defense Artillery

192 THE COAST ARTILLERY JOURNAL
ment question and adjustment of fire is possible, at least under certain conditions.
In exactly what percentage of engagements it will be possible is a
figure shrouded in the mists of futurity. To most proponenti of adjustment
it seems, quite logically, that (having prepared the fire) to continue firing at
a target without result and with no attempt to adjust borders on inaction, an
unforgivable military crime.
When we were told that antiaircraft fire must be prepared, with what
problem were we confronted? A point in space must be selected and a series
of bursts fired at that point, the location of each burst being computed and
located by very inaccurate means. The deviation of the bursts, as represented
by their determined C. 1., from the point selected is due to the inaccuracies of
locating the bursts; to errors in the firing tables; to non-standard muzzle
velocities, caused by peculiarities of the powder lot, erosion of the gun, the
temperature effort on powder, and other variants affecting muzzle velocity; to
variations in weight of the projectiles; to elasticity effects; to wind; to drift;
to rotation effects; to variations in density and in the moisture content of the
air; and to any of the other causes of non-systematic error that might prevent
the attainment of a true C. I. in the few rounds fired, or causes of systematic
error that impel the C. 1. to refrain obstinately from falling where it should.
The summation of all these innumerable effectsis a distortion of all trajectories,
for which complicated changes, flat corrections made at one point in space,
were supposed to offer a correction! It is true that something was known about
wind and drift effects and approximate corrections for these two could be
applied, but even if accurately applied, these corrections would be lost in the
maze of the unknowns. The problem was incapable of so simple a solution
then and is incapable of so simple a solution now.
The proper opening wedgeto drive into this knotty question is one to reduce
the most important ballistic variations to known and accurately applied corrections.
The Director M-l (Vickers) computes and applies its own wind and
drift corrections. Muzzle velocity corrections may be effectedby placing charts
for the specific muzzle velocity obtained on the time-of-flightand altitude-fuze
range drums. To determine the muzzle velocity developed the field chronograph
has come into being and the Ordnance Department has caused to he
published the differential effect of temperature on the powder.
A data computer constructed by the Ordnance Department, and now undergoing
further development and perfection, is of such design that ballistic corrections
are made with greater ease and accuracy than is true of the Director
M-l. In addition to the automatic application of wind and drift corrections,
muzzle velocity corrections may be made instantly by setting the desired value
on a scale graduated in foot seconds. Furthermore, a ballistic coefficient
correction is provided whereby the battery commander may take cognizance of
variations in the ballistic density.
Quite a few sources of systematic error remain, but a large bite has been
taken from the total number and the trial-shot problem has been reduced in
complexity thereby. An extensive trial shot study has just been completed