COAST ARTILLERY, JOURNAL - Air Defense Artillery

PROFESSIONAL NOTES 563
The eight practices were fired in the following order: Battery A, mortars;
E, 12-inch guns; F, lO-inch guns; B, mortars, all on July 12; and on July 13,
D, mortars; H, 12-inch guns; G, 10-inch guns; and C, mortars. This made it
necessary for the spotting detail to move between each two practices. Only one
spotting bo~rd was available, but there were enough azimuth instruments. available
for all of the spotting stations used. The moves were made without delaying the
practices.
Notwithstand the brief traiuing of the detail, they lost only one of' the 32 shots
fired by the gun batteries at ranges varying from 9,200 to 10,500 yards, and for
the 31 splashes spotted the mean difference between the spotters' report and the
longitudinal deviations subsequently obtained by the plot of the splashes from
the camera and lateral deviation records was only 27 yards. Thirteen, or 42 per cent.
of these shots, were spotted within 12 yards, and 71 per cent were spotted within 30
yards. Airplane observation was available for seven of these shots, one of which
was lost by the airplane. For the other. six the results obtained by the terrestrial
spotters and the airplane observer were practically identical, the former being
somewhat closer and so much more rapid that the report had been received from
the terrestrial spotting detail and the resulting correction made and applied before
the airplane report was received. The airplane report was transmitted by radio
to the radio station and thence relayed by telephone, the telephone wire being
kept open.
The result in the case of the four mortar p~actices was not so satisfactory as
to accuracy, probably on account of the special situation obtaining at the battery
which was fired. The entire target course is hidden from this battery by a large
island, on the left end of which the primary station is located. The observer of
lateral deviations and the observer of the azimuth of the target at the instant
of splash were both placed at the primary station on the island where one of the
spotting observers was also located and an effort of the details for the three
functions to cooperate seems to have worked badly. Under this arrangement, also,
the lateral deviations on which, with the camera recor~, the plot of deviations is
based, being observed at an angle of from forty to eighty degrees with the target
course and most of the impacts being nearer the forty than the eighty degree end
of the course, a slight error by thl" observer of lateral errors might make a large
error in plotting the splash. Excessive armament errors developed tend to encourage
the suspicion that all of the spotting errors show might not in fact have been
spotting errors.
Be that as it may, the average spotting error shown for the mortar practices
on the twelfth was 209 yards, and on the thirteenth, 60 yards, or' a mean of 132
yards for the entire 30 mortar shots observed, two having been reported as lost.
The result obtained in the gun practices is believed to be the more reliable
criterion of the system. Three errors of 30 yards in the spotting were directly due
to a fault of the particular board used, the head of the pivot extending 30 yards
from the center of the board and concealing the 20-yard line passing under it for
a distance of approximately 60 yards. In each of the cases referred to a shot
falling 20 yards short was reported ten yards over through the inability of the
board operator's eye to carry the line through this area where it could not he
actually seen. So large a head for the pivot was not necessary and this type of
error also would be minimized "ith a larger board.
The result was obtained with a board having a scale of 160 yards to the
inch and reading lines spaced 20 yards apart. With a scale of 100 yards to the