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MODEL OF 1904
( THREE PLATES)
JUNE 15, 1905
REVISED JULY 15, 1906
REVISED DECEMBER 5, 1907
REVISED APRIL 2, 1912
aOVBRNMBNT PRINTING OPPICE
Office of the Chief of Ordnance,
Washington, Anril 2, 1912.
This Manual Is published for the information and government of the Regular
Army and Organized Militia of the United States.
By order of the Secretary of War :
Brigadier General, Chief of Ordnance,
3-INCH TELESCOPIC SIGHTS,
MODEL OF 1904.
(The important changes in this pamphlet are shown in boldface type.)
(The telescopes for these sights were designed by the Warner & Swasey Com-
pany, Cleveland, Ohio.)
1. The advantages gained by the use of a telescope in laying a
piece consist of a decrease in personal error and an increase in power
of vision. A telescopic sight enables a gunner to see clearly an
object which is indistinct to the naked eye and to lay a gun on it with
facility and accuracy.
2. For the designation of parts see Plates I, II, and III, and the
list attached hereto giving the nomenclature. Plate I shows a tele-
scopic sight and cradle with a bracket for a barbette carriage. Plate
II shows same with arm for a disappearing carriage. Plate III
shows a sectional view of the telescope.
Sights for Barbette Carriages.
8. The principal parts are the telescope (1, 2, 3, 6, 9, 13, PI. Ill),
the sight bracket (25), the cradle (15), the open sights (4, 16), the
sight shank (24), the range drum (30), the gear case cover (31), the
elevating worm (43), the fulcrum (21), the yoke (40), the cables and
electric lamps, the deflection scales (45), the elevation scale (34), the
deflection worm (47), and the elevating gear shaft (46).
4. The sight bracket is bolted to the carriage by means of the feet.
Tlie cradle is assembled at the forward end to the sight bracket by
means of the yoke and fulcrum. The yoke shaft seats in the sight
bracket and is keyed in place ; the fulcrum axes have bearings in the
two sides of the yoke permitting rotation for elevation and depres-
sion, and the fulcrum has a short vertical shaft on its underside to
which the forward end of the cradle is assembled so as to allow rota-
tion in azimuth only. At the rear end the sight shank is assembled
between the sight bracket and the gear case cover, being held in place
by the gear case cover and the elevating gearing. The cradle is
assembled to the sight shank by means of its head (which is also the
deflection worm box) and the deflection worm, the latter being
seated in the box and meshing into a worm segment cut in the cradle.
The front and rear faces of the deflection box and the head of the
sight shank are arcs of circles having their common center on the
axis of the vertical shaft of the fulcrum, and the front and rear faces
of the sight shank and its seat are arcs of circles having their com-
center on. the central line of the fulcrum axes. The sight shank stop
(73) attached to the lower end of the sight shank limits the movement
of the sight shank in elevation.
5. The elevation of the sight and the rotation of the range drum
are accomplished by the elevating gearing, consisting of the elevating
worm and the elevating gear shaft with its worm gear and spur gear,
the latter two being on one piece. The elevating worm engages the
worm gear and the spur gear engages the sight shank rack. The
piece on which these two gears are cut is mounted on a squared sec-
tion of the elevating gear shaft, which is also the range drum shaft.
The range drum is also mounted on this shaft and is held in place
by the friction of a nut on a washer bearing against the drum and
the friction of the drum on a shoulder of the shaft. A ribbon spring
11 feet long and of German silver is secured at one end to the ele-
vating gear shaft, is wound several times around the shaft, and has
the other end secured to the gear case cover. The cover is bolted to
the sight bracket. By rotating the elevating worm, the elevating
gear shaft is turned, adding to or releasing tension on the spring,
depressing or elevating the cradle by means of the sight shank and
rotating the range drum. The spring serves to equalize the force
required to depress and elevate the cradle. The gear case cover and
the bracket serve to protect the elevating gearing, the spring, and the
range drum. The range scale pointer is attached to the cover.
6. An elevation scale of Grerman silver is dovetailed into the rear
face of the sight shank, and reads to 6 minutes from zero to 16
degrees. The pointer is on a piece of German silver dovetailed into
the sight bracket.
7. Deflection is obtained by rotating the deflection worm which is
seated in the deflection woim box and meshes into a worm segment
cut into the cradle where the box is seated.
8. The deflection scale, of German silver, is secured to the rear
end of the cradle and reads to 0.05 of a degree, which equals 3 min-
utes, over an arc of 4 degrees, beginning with 1 degree on the right
hand. The 3-degree mark gives no deflection. The pointer plate is
secured to a bracket which is screwed to the under side of the sight
shank head. This bracket has, at the rear end, the deflection lamp
bracket and a lug that works in a groove in the end of the cradle.
9. The open sight consists of a peep sight in rear and a cross si^t
in front, the former mounted on the eye-end telescope clamp and the
latter on the cross-sight holder. It is for use in picking up an object
10. Each flight is provided with two small electrio lamps of about
2 candlepower, and of the following voltages: 110-volt when used on
disappearing carriages monnted in emplacements with 110 or 220 volt
mains; 74-volt when used on other than disappearing carriages with
220- volt mains; and 36-volt when used with 5-inch and 6-inch barbette
carriages with 110-volt mains. One of these lamps illnminates the cross
wires, giving bright lines in a dark field, and the other illuminates the
deflection pointer. They are connected with the electric circuit by the
cables and plug connections. The lamp that illuminates the cross wires
is placed in a holder that is secured to the eye end of the telescope tube
on the right-hand side. Two small mirrors deflect the rays of light
through two elongated openings cut through the focusing sleeve and
telescope tube about 90 degrees apart. These openings are so arranged
that the light from each mirror is thrown upon the full length of the
wire opposite. The intensity of illumination of the cross wires may be
varied by turning the lamp bracket diaphragm which has two V-shaped
openings which pass over slots in the lamp bracket, thereby varying the
area of the light openings.
11. The principal parts of the telescope are the telescope tube (9), the
objective (56), the Porro erecting prisms (55), the draw tube (57), the
cross-wire holder (53), the focusing sleeve (51), the focusing ring (3),
and the eyepiece (1, 2, 48, 49, 50, 52).
12. The telescope tube is the principal piece to which the other parts
are assembled. The objective is a triplet seated in a cell that screws
into the forward end of the telescope tube, and gives a 3-inch clear
aperture. The Porro erecting prisms are two in number, which are re-
tained in the prism holder by flat springs. Brashear-Hastings prisms
having cemented surfaces are used in sights Hos. 1 to 26. In sights Hos.
27 to 297, inclusive, the prism holder and cover are made in one piece.
In sights after Ho. 297 the cover is separate from the prism holder.
13. The cross wires are secured to a ring by four clamps, and are
at right angles to each other. The cross-wire holder (63) is secured
to the draw tube by screws. The draw tube is assembled to the focus-
ing sleeve so as to allow longitudinal motion of the former when the
focusing ring is rotated, and to force rotation of the tube when the
focusing sleeve is rotated. The sleeve is screwed into the rear end
of the telescope tube by a thread of tight fit, and will be locked in
place by a set screw (60). The focusing ring is seated on the focus-
ing sleeve by a threaded surface, its motion being limited by the
telescope tube in front and the focusing-sleeve nut in rear. When
turned, it transmits longitudinal motion to the draw tube and
14. Two eyepieces are fumislLed. Each consists of the eyepiece tube
(50), the field lens (52), the eye lens (49) in its holder, and the eyepiece
cover (1). The eyepiece tnbe is screwed into the draw tube and carries
the field lens and the eye lens with its cell, the cover being screwed to
the latter. There is an amber glass shade in a holder (48), that is
pivoted so that it may be nsed or not, as desired. It is provided to protect
the eye from a glare of light. The eyepiece of power 12 should be used
under conditions of poor illumination.
15. The front end of the telescope is provided with a movable
shutter (13) for the protection of the objective.
16. The clear aperture of the telescope is 3 inches, the focal length
of objective is 17.25 inches, the magnifying powers of the two eye-
pieces are 12 and 20 diameters, and the fields are 3.6 degrees for the
12-power eyepiece and 2.6 degrees for the 20-power.
17. The image is erect, the erection being secured by the Forro prisms,
each of which twice totally reflects the pencil of light at an angle of 90
degrees, so that it emerges parallel to the entering pencil and in the
original direction. The path of an axial pencil of light is shown on Plate
m, giving an illustration of the erecting process, in which, however, the
90-degree angles are not all projected as 90 degrees, because of the relative
position of the prisms.
18. The telescope is secured in position by clamps and is located
by six accurately bored segmental projections, four on the cradle and
one on each clamp. A locating lug on the front clamp fits into a
recess in the telescope, thus bringing the vertical wire plumb.
19. For those carriages in which the gun is carried in a cradle, the
sight bracket is bolted by means of the feet to seats which form parts
of the gun cradle. Thus the motion of the bracket conforms to that of
the gun, and when the sight is properly assembled to the carriage and
the elevation reading is zero, the optical axis of the telescope and the
axis of the bore of the gun will remain in parallel planes at all elevations.
Therefore, if the sight be set at the elevation required for the range of
the target, and then laid upon it, the gun will automatically receive the
same elevation. Since the deflection movement of the sight is independent
of the gun, any deflection necessary may be given to it without affecting
the elevation. The elevation scale on the sight shank is normally not
20. The sight brackets for barbette carriages are lefts and rights.
Plate I shows a right-hand sight. It is expected that eventually all
left-hand sights will be removed from 5-inch and 6-inch barbette carriages.
Sights for Disappearing Carriages.
21. The sights for disappearing carriages differ from those for bar-
bette carriages in that a sight arm is substituted for the sight bracket,
and a different method of attachment is used. See Plate 11.
22. The sight arm differs from the sight bracket in shape, has an
elevation guide, and the feet of the sight bracket are replaced by
seats for two pins.
23. All disappearing carriages are constructed for the mounting of
the 3-inch telescopic sight on the left side of the carriage, except the
6-inch disappearing carriage, model of 1905. The top of the sight
standard ends in a horizontal flange surmounted by a cylindrical axis,
upon which is centered a sight-arm bracket with a flange resting on
the flange of the sight standard. The sight-arm bracket is forked and
provides seats for the pins by which the sight arm is attached. The
sight-arm bracket has a small motion in azimuth and can be set in its
proper position by lugs and adjusting screws, then clamped by screw
bolts passing through its flange and into that of the sight standard.
The method of attachment of the sight to the carriage is more fully
described in the pamphlets descriptive of the various models of carriages.
Sights of Nearly the Same Design as the Model of 1904.
24. There are in service 26 sights, numbered from 1 to 26, both
inclusive, which are nearly the same as those described above. The
differences are due to substituting in the latter Porro double reflect-
ing prisms for the Brashear-Hastings erecting prisms u^d in the
25. The telescopes of these sights are differently shaped from the
model of 1904, being practically symmetrical about the axis; they
are longer by about 3^ inches, the peep sight is directly over the
eyepiece, the rear clamp is differently shaped, the sides upon which
the shutter and clamps are hinged have been reversed, the adjusting
arrangements for the cross- wire holder are different, and the diam-
eters of bearings on the telescopes and cradles for seating the tele-
scope are A ii^ch smaller than on the model of 1904.
Method of Assembling the Sights and Locating the Pointers.
FOR barbette carriages.
26. In assembling the brackets for the barbette carriages, great
care should be taken to see that the seats are level in both directions,
and that burrs, paint, and rust are removed from them and the feet
of the brackets. A small obstruction of this kind will throw the
sight shank out of plumb. In setting up the bolts, all should be
brought to a firm bearing before any are set up tight.
27. The elevation pointer is marked by the manufacturer of the
sights, since there is no adjustment for it on the carriage. The ele-
vation pointer should be cut at the works of the builder of the carriage
to allow for any possible inaccuracy in the seats and the deflection
pointer should be put on at the emplacement after the gun is mounted.
28. After the sight is assembled to the carriage and while the gun
is at zero elevation the sight should be accurately leveled and the
pointer cut exactly opposite the zero of the elevation scale.
29. The position of the deflection pointer may be detennixied by adjust-
ing the telescopic sight so that its axis intersects the axis of the gon at
mid range. The pointer should then be set exactly opposite to the 3-degree
mark on the deflection scale.
FOR DISAPPEARING CARRIAGES.
30. The deflection pointer is cut by the manufacturer of the sight, but
the axis of the telescopic sight and the axis of the bore of the gun should
be adjusted at the emplacement, so that they intersect at mid range.
When the sight is in the correct position the bracket should be clamped
and a light line cut so as to extend over both the flange on the bracket
and that on the sight standard.
31. The range drums for these sights will not be used as such, nor
will they be graduated. The sight shank elevation scales are also not
used. The movement of the sight in elevation allows for variations in
the angle of site of the target.
32. The cross wires are rendered distinct by screwing the eyepiece
in or out, and this adjustment has no other object. If the telescope
is frequently used by the same observer, the eyepiece can be reset
at the correct position by using the graduations on the outer rim
in connection with the pointer on the focusing sleeve nut. After
bringing the cross wires into distinct vision by adjusting the eye-
piece, the wires may be brought into the focal plane by turning the
focusing ring until the object appears distinctly and does not seem
to shift when the- eye is moved from side to side of the eyepiece.
This adjustment is impossible if the object is too close to the telescope.
33. The cross wires are mounted on the cross-wire holder, which is
held in position by four adjusting screws which pass through elongated
holes in the focusing sleeve. These screws may be reached by first re-
moving the focusing sleeve nut and unscrewing the focusing ring until
the slotted screws can be seen through the elongated openings in the
34. When adjusting the cross wires the collimating telescope furnished
with the optical repair kit should be placed in the proper rings and
securely clamped in the ,sight cradle, and when properly adjusted should
be sighted on a target haying plnmb and horizontal lines. The telescopic
sight is now placed in the cradle with its axis coinciding with the axis of.
the collimating telescope.
35. The cross wires shoald be adjusted by means of the adjusting screws
to coincide with the same plumb and horizontal lines which were seen
through the collimating telescope.
36. The slotted holes in the focusing sleeve permit a slight rotary
motion of the cross-wire holder to secure vertical and horizontal align-
ment. The focusing sleeve should always be screwed into the telescope
tube and locked in place with a set screw (60).
37. The adjustment of the cross wires of the sights numbered from
1 to 26 is made by unscrewing the focusing sleeve nut and the focusing
ring until access is given to the capstan head adjusting screws that
secure the cross-wire ring. These screws should be loosened, the
adjustment made, and the screws again set up.
38. To adjust the tension of the range drum spring, run the sight
shank rack out of mesh, turn the balanced handwheel to the right
to relieve tension or to the left to increase tension and reengage the
rack. When the cradle and telescope are in place and the eleva-
tion is 8 degrees, the force required to rotate the handwheel should
be the same for both directions. The cradle must first be disengaged
from the head of the sight shank before this adjustment is made.
Care and Preservation.
39. Telescopic sights are necessarily delicate instruments and must
not be subjected to rough usage, jars, or strains. When not in use,
the telescope should be kept in its leather case and should be stored
in a dry place. It should be occasionally examined to insure its not
being corroded by tannic acid from the case, and all traces of dust
or moisture should be removed before putting it away.
40. To obtain satisfactory vision, the glasses should be kept per-
fectl}' clear and dry. In case moisture collects on the glasses, place
the telescope in a gentle warmth ; this is usually sufficient to remove
it. Material issued for cleaning of lenses only should be used^ care
being taken that the cleaning material does not contain any dirt or
grit. The glasses will seldom require cleaning on the inside; but,
when necessary, they should be unscrewed, and by a competent person
only. The object glass must always be kept screwed home, except
when removed for cleaning.
41. The erecting prisms should not be removed from the prism
holder except by a person with special training in the care of tele-
scopes^ and if they need repair, report should be made to proper
authority. Semoval is apt to disturb the adjustment, and finger
marks or lint will cause difficulty.
42. The cross wires ai-e unprotected when the eyepiece is removed,
and great care must be exercised not to touch them, as they are very
delicate. No attempt should be made to clean them, except by
43. The sight bracket (or arm) and cradle should never be removed
from the carriage unless the carriage is to be dismounted. When not
in use, these parts should be kept protected by the covers provided for
the purpose. All bearing surfaces should be kept thoroughly oiled,
especial care being given to the worm box, sight shank, and bearings
for the telescope, which are of steel. Care should be taken not to
remove the oil in putting on the cover. The oil should be wiped off
before use. The cover should be removed and the sight brackets (or
arms) , etc., examined at least once in every two weeks, and the cradle
should be moved in elevation and deflection, so that as much as pos-
sible of the sight shank and worm box can be inspected.
No oil should he allowed on the surf aces of the lenvses and prisms.
44. Special care should be taken in the use of the small electric
lamps, as they are fragile. Each lamp should seat in its receptacle
not less than one and one-half turns.
Dismantling and Assembling.
45. General instmctions for disassembling and cleaning are g^iven in
pamphlet No. 1796, Instructions for the Care, Preservation, Bepair, and
Adjustment of Instruments for the Fire Control Systems for Coast and
Field Artillery, paragraphs 24 to 28, and 35 to 38, inclusive.
46. If a sight is packed for shipment, special attention should be given
to the blocking of it in its packing box to prevent all movement of the
sight during transit. The telescope should be packed separately.
47. When ordering spare parts, use the nomenclature given below.
Nomenclature of Sights.
(Plates I. II, and III.)
1. Eye piece cover.
2. Eye piece dial.
3. Focusing ring.
4. Peep sight.
5. Eye end telescope clamp.
6. Prism holder.
7. Deflection worm knob.
8. Clamp pin.
9. Telescope tube.
10. Split pin for clamp pin.
11. Telescope lamp bracket.
12. Cell end telescope clamp.
13. Objective shutter.
14. Twisted hook.
16. Cross sight holder with sight (complete).
17. Clamping screw.
18. Yoke cap.
19. Cross sight screw.
20. Deflection pointer bracket.
22. Elevating wheel.
23. Objective shntter handle.
24. Sight shank.
25. Sight bracket.
26. Deflection pointer bracket screw.
27. Lamp cord.
28. Plug connection for lamps.
29. Lamp holder for deflection scale.
30. Bange drum with range drum scale.
I»l. Gear case cover.
H2. Lamp cap.
33. Telescope lamp holder.
34. Sight shank elevation scale.
35. Yoke cap bolt.
36. Split pin for yoke.
37. Sight arm.
38. Deflection scale screw.
39. Lamp bracket screw.
41. Focusing nut.
42. Focusing nut screw.
43. Elevating worm.
44. Focusing sleeve nut.
45. Deflection scale.
.46. Elevating gear shaft.
47. Deflection worm and nut.
48. Amber glass holder with disc (complete).
49. Eye lens.
50. Eyepiece tube.
51. Focusing sleeve.
52. Field lens.
53. Cross-wire holder.
54. Cross wires.
55. Erecting prisms (Porro).
57. Draw tube.
Digitized by VjOOQIC
68. Cross-wire holder screw.
59. Gross-wire clip.
60. Focnsing sleeve locking screw.
61. Eyepiece (complete) 12 power.
62. Eyepiece (complete) 20 power.
63. Oear case cover bolt and nut.
64. Prism spring.
65. Prism holder screw.
66. Bange pointer (right hand).
67. Bange pointer (left hand).
68. Bange pointer screw.
69. Spring cover.
70. Spring cover screw.
71. Bubber hood for 12 power.
72. Bubber hood for 20 power.
73. Sight shank stop.
Office of the Chief of Obdnance,
Washington, April 2, 1912.
June 15, 1905.
Revised July 15, 1906.
Revised December 5, 1907.
Revised April 2, 1912.
Form No. 1955.
Ed. Aug. 24-17-600.