COAST ARTILLERY, JOURNAL - Air Defense Artillery

MORTAR FIRE CONTROL 511
turned, i. e., new data appeared on mechanical display board before
firing instant for the old data. The special board was held so as to
display the data in use until firing time. As the stage of training improved
both sets of data were written on the special board, as a rule,
when time came to turn it, and there was time available for "repeats"
between the operators on the display board and the operators in the
plotting room.
15. A recorder in each pit recorded all data displayed .and compared
the 3-bell data shown on the two display boards. If 3-bell data
did not check he signalled the fact to the pit commander who commanded
"relay." The recorder also noted whether the intermediate
2-bell data shown on the display board were approximately half-way
in magnitude between the 3-bell data then displayed and last preceding
3-bell data he had recorded.
16. Under present regulations a recorder is required in the em.
placements and pits of all batteries. It is desirable to provide a means
for continuing the fire of a battery during periods of interrupted com.
munications between plotting room and pits or emplacemen".. The
Board has devised a means for recording easily firing data sent to, or
displayed in, the pits or emplacements, for checking interpolated
data or predicted data after several predictions have been obtained,
and, when communications to the plotting room are interrupted, fm
continuing the flow of reasonably accurate firing data to the guns for
a short period of time. The device is called a check-back board.
17. a. The check-back board referred to is simple and requires
but one operator-the recorder. It consists, in the case of mortars, of
a time-elevation spiral (of the type described in Coast Artillery Board
Project No. 75) mounted adjacent to an 8-inch by 20-inch piece of
10/10 cross-section paper on a drawing board twenty inches square.
Figure 3 is a photograph of the device.
b. The time-elevation spiral is graduated in elevations corresponding
to each ten yards of range in each mortar zone. The cross.section
paper shown above the spiral is numbered in azimuth to a scale of one
inch equals one degree to cover the field of fire of the battery. Pieces
of vellum paper are tacked over the spiral and the cross section paper.
c. The operator records the zone and elevation shoVr'Ilon the special
display board by a pencil check mark on the vellum at the elevation
for the indicated zone. Similarly he makes a check mark on the cross
section paper at the azimuth shoVr'Il.The data can be synchronized by
indicating "time 10," "time 20," etc., by figures or symbols penciled
on the vellum.
d. The distances between successive check marks on the device
affords a check upon the accuracy of succeeding predictions and inter-