Improvements relating to the Aiming or Pointing of Guns at Sea.
Year: 1890

page_text: Date of Application, 9th Sept., 1890-Accepted, 15th Nov., 1890
COMPLETE SPECIFICATION.
Improvements relating to the Aiming or Pointing of Guns
at Sea.
I, BRADLEY ALLAN FISKE of the City of New York, State of New York, United
States of America, Lieutenant in the United States Army do hereby declare the
nature of this invention and in what manner the same is to be porformed to be
particularly described and ascertained in and by the following statement :-
My invention relates to a new method of pointing guns located upon a vibrating,
heeling or rolling platform, such as a ship, upon a distant target: and consists (after
determining the angle of elevation above the horizontal which it is necessary to give
the gun in order to cause the projectile to traverse the given range) in adjusting a
telescope movable about a transverse axis approximately parallel to that of the gun
at an angle to the axis of the bore of said gun equal to said predetermined angle of
elevation, and then noting the moment when the line of sight of said telescope so
adjusted intersects the target.
In the accompanying drawings,
Fig. 1 illustrates a vessel on an even keel, showing the vessel's deck, the gun and
the telescope all horizontal and parallel.
Fig. 2 shows the vessel heeled over a determinate angle, the gun still remaining
parallel to the deck, but the telescope disposed with reference to the deck over an
angle equal to that of the heel of the vessel.
Fig. 3 shows the vessel heeled over a determinate angle less than that shown in
Fig. 2, the gun being elevated above the deck through the remaining part of
that angle, and the telescope depressed over an angle equal to the heel of the
vessel.
Similar letters of reference indicate like parts.
A represents a section of the hull of a vessel, BC the water line, and D E the line
of the deck. F is a gun mounted on the deck and capable of being elevated or
depressed, turning on its trunnions G. H is a telescope or spy-glass supported on
transverse pivots or trunnions in any suitable way above the deck, and also capable
of being turned on vertical pivots so as to point at any object.
In Fig. 1 the vessel A is shown on an even keel, the deck line D E, axis of the
gun F and axis of the spy-glass H all being parallel and horizontal.
Let it be assumed that the gun is to fire at a target located at such a distance from
the ship that the necessary elevation to be given to the gun above the horizontal
would be (to illustrate) two degrees. But suppose the ship heels over as indicated
in Fig. 2, so that the deck line makes an angle EIC equal to two degrees. Then,
clearly, the axis of the gun being parallel to the deck will make an angle of two degrees
with the horizontal, and thus by the rolling or heeling of the ship the gun will be
brought to the desired elevation. If it be then fired, its projectile will (as assumed)
traverse the distance to the target. The object of the telescope H is to determine the
moment when the vessel in rolling or heeling reaches the point at which the gun
attains the desired elevation. To this end, as soon as the extent of elevation is
determined, the telescope is set so that the angle between its axis and the axis of the
gun shall equal this angle. That is, assuming as before the angle of elevation of the
gun to be two degrees, the object end of the telescope is depressed two degrees.
(Dotted line Fig. 2.) Therefore the angle between the line of sight of the telescope
and the axis of the bore of the gun will be two degrees. The observer now looks
through the telescope until he sees the cross hairs of the telescope intersect the target,
which may be assumed in all cases without material error to be located in a level line
drawn from the telescope. In order that the cross hairs may intersect the target,
he vessel must heel or roll so as to bring the telescope back to the horizontal, or in

page_text: the position indicated by the full lines Fig. 2. When this happens, the gun is in the
position shown and hence at the desired elovation.
Suppose, however, that, by reason of the smoothness of the sea, the vessel does not
roll, or heel, sufficiently to elevate the gun to the desired extent. Assuming this, as
before, to be two degrees, let one degree bo the maximum elevation producible by the
heeling of the vessel. These conditions are illustrated in Fig. 3, the angle between
the deck line DE and the water line BC being one degree. The gun is then
elevateri on its trunnions over an angle of one degree; and inasmuch as the angle
between gun and telescope must equal that of the desired elevation of gun, the tele-
scope is depressed one degree, so that the angle between gun and teloscope as before
becomes two degroes. Therefore when the telescope is brought level by the heeling
of the ship, and the target sighted through it, the gun will stand at an elevation of
two degrees above the horizontal; one degree being obtained by the heeling of the
vessel, and one degree by the gun's own elevation on its trunnions G. Of course,
the gun may be laid at any angle of elevation and the telescope adjusted
conformably.
The assumption made in the foregoing that the line from the telescope to the target
floating on the water is a horizontal line, is strictly true only when the telescope
points at a part of said target which is at the same height above the water as
the telescope itself. But under ordinary conditions of practice, this refinement may
be neglected, and the gun fired when the cross hairs of the telescope cut any part of
the target.
Among the advantages gained by my aforesaid method are that it does away with
the use of all mechanical contrivances, such as pendulums, spirit levels, etc., and allows
the gun to be accurately adjusted in elevation with reference simply to the true
horizontal line. It renders unnecessary frequent adjustment of the gun itself on its
trunnions to effect changes in elevation, the telescope being correspondingly depressed
instead. It places the determination of the instant of firing the gun in the control of
a person distant therefrom, and hence in a position away from the excitement and
hurry prevailing in the immediate vicinity of the gun; and finally, the piece can be
sighted much more accurately by means of the telescope than is possible by the use
of the rough sights on the gun itself.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, 1 declare that what I
claim is :-
Pointing a gun located on a rolling, heeling, or vibrating platform, by adjusting a
telescope also located on said platform and movable on a transverse axis approximately
parallel to that of the gun, at an angle to the axis of the bore of the said gun equal to
a certain predetermined angle of elevation necessary to cause the projectile fired from
said gun to travel to a given target; and second, noting the moment when the line of
sight of said adjusted telescope is caused by the movement of said supporting platform
to intersect said target.
Dated this 9th day of September 1890.