S 14 AND 17
17B10. Columns 14 and 17

“Deviation for lateral motion of gun perpendicular to line of fire, speed, 10 knots.” By “motion of gun” is meant the
velocity imparted to the projectile due to motion of the firing ship, aside from the velocity imparted by the powder charge.

velocity of 16.89 foot-seconds, in the horizontal plane. The same ship firing dead astern reduces the horizontal component
of initial velocity by the same amount.  Firing on the beam causes a velocity component across the line of fire in the
direction of motion of the ship.

In the case of firing dead ahead, the range would be increased by 16.89 X Tf/3 yards.  But this is the value found in
columns 15 and 18, since the target motion was computed by using this very formula and with these same values.

a person standing on deck on a moving vessel will feel an apparent wind, equal in force to the speed of the vessel.
It may therefore be said that a projectile fired from a moving vessel, in still air, is opposed by an apparent wind equal
in force but opposite in direction to the motion of the vessel. The effect of such an opposing wind may be found in

the equivalent of the effect of an equal component of target motion less the effect of an equal component of wind.”
This does not mean that target motion, as such, enters into the problem in any way. It does mean that the value
of the change of range if the gun were fired in a vacuum, would be computed in the same manner in which the
However, since the gun is fired in air, this effect is opposed by a force which is the same as that of an equal
component of wind blowing against the projectile. This relation should be thoroughly understood, as it will be
employed repeatedly in this text.

This statement may also be expressed as:

Column 14 = column 15 — column 13, and

Column 17 = column 18 — column 16.

is due to the fact that columns 14 and 17 actually are computed from formulas, the results plotted, and the curves faired.)