September-October - Air Defense Artillery

68
yards of range, based on firing table data for shell HE-T
(SE M3AI) ~lk II w/fuze, PD M64 Al (muzzle velocity
2,700 f/s). An appropriate correction can be made in opening
range when ammunition of different muzzle velocity is
used. Two scales are etched on the perimeter of the range
drum, graduated from 1,400 to 4,400 yards on the outer
scale, and 4,400 to 5,975 yards on the inner scale (See Figure
4). Subdivisions of 50-vard intervals are used from
1,700 to 4,000 yards range, ~nd 25-yard subdivision from
4,000 to 5,975 yards range. Calibration of the range drum'
was accomplished in the following manner: using FT
40-AA-A-2, the quadrant elevation for ground ranges from
1,500 to 6,000 yards was determined, corrected for type of
ammunition. Setting the gun by gunner's quadrant to an
elevation corresponding to 1,500 yards range, the 1,50o-yard
graduation was marked on the drum opposite the indicator ..
The process was repeated for each 100 yards up to 6,000
yards range, taking care not to overtravel and thereby introduce
a backlash error. Subdivisions were interpolated onto
the scale. Approximately two complete turns of the eleva.
tion hand crank were required, which necessitated graduating
both ~dges of the drum.
(d) Orient and engage the range drum, the gun is carefully
levelled and average range selected, and the gun elevated
to the correct range by means of a gunner's quadrant.
THE COAST ARTILLERY JOllRNAL
U. S. Nary Photo
American PO\Vs in the compound at Yokohama shout and
wave at a carrier-based plane.
September-Octo
The handwheel is then disengaged, the correct range r
ing set opposite the indicator, and the handwheel ree
gaged. A collar can be placed on the handwheel to insue
its remaining engaged, thereby maintaining proper orienta
tion. In order to prevent an incorrect range setting duej
being one or more turns off, a reference mark should
made on the body elevation plate, indicating the upper a
lower range settings on the drum.
(e) A height-of-site graph has been developed to faci!
tate accurate laying of the gun in elevation for the initia
round (See Figure 6). l
(f) Errors due to backlash in the elevation and azimut
gears are very small, and can be virtually eliminated b
"coming into the target" from the same direction each time
(g) By use of the azimuth and range drums, it is pos_
sible to conduct accurate unseen fire by 40mm guns. The
initial firing data is determined by map study, and the gu~
is laid on target by means of compass, aiming circle, or othd
standard field artillery methods. After the initial round
corrections in range can be set directly by turning the ele
vation hand crank; deviations in azimuth are translated intc
mils, and set directly on the gun by traversing with the azi
muth hand crank, right or left, the required amount. Fire
may be quickly transferred from one target to another within
the limitations of the range and azimuth drums.