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SERVICE ASSEMBLY - CHAP. IV O.P. NO. 747

TOOLS

1. Prior to the development of the Mark 6 Mod. 1 depth charge pistol and booster extender, sets of service tools were furnished for use with Mark 6 pistols and booster extenders. This original service set consisted of the following tools contained in a canvas bag.

1 Extender Testing Tool (Dwg. 180387-1 to 5).

1 Depth Setting Wrench (Dwg. Nos. 180387-10, 180387-A-10, or 180387-B-10).

1 Detonator Holder Wrench (Dwg. 180388-3).

Tools

2. The development of the Mark 6. Mod. 1 (deep setting) pistol and the Mark 6 Mod. 1 booster extender has necessitated an additional special tool to the regular tool set for shipboard use. This tool, the Packing Nut and Gland Wrench (Drawing 18038815), is being procured in quantities sufficient for issue to Forces Afloat at any early date, and will be issued in one of two distinct ways: (a) as a separate unit, or (b) as a single tool having a Detonator Holder Wrench (Dwg. 180388-3) at one end and a Packing Nut and Gland Wrench (Dwg. 180388-15) at the opposite end.

3. A screw driver for making the deep settings on the Mark 6 Mod. 1 pistol will also be necessary. Depth setting wrenches procured for service tool sets

 

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of future issue will be manufactured with a screw driver on the end of the handle. It is not intended to replace depth setting wrench now in use with the new type, since any ordinary medium sized screw driver in stock on board ship may be used for the above purpose.

NEW SERVICE SETS

4. There will be two chief sources of supply for the new tool sets, the Naval Mine Depot, Yorktown, Virginia, and the Naval Ammunition Depot, Hawthorne, Nevada. These new service tool sets, when issued complete, will consist of either of the following assortments:

(a)

1 Extender Testing Tool (Dwg. 180387-1 to 5).

1 Depth Setting Wrench with screw driver at opposite end (Dwg. 180387-C-10).

1 Detonator Holder Wrench with Packing Nut and Gland Wrench at opposite end (Dwg. 180388-3 and 15).

(b)

1 Extender Testing Tool (Dwg. 180387-1 to 5).

1 Detonator Holder Wrench (Dwg. 180388-3).

1 Depth Setting Wrench with screw driver at opposite end (Dwg. 180387-C-10).

1 Packing Nut and Gland Wrench (Dwg. 180388-15).

5. When vessels, at present equipped with the old type tool sets, are issued Mark 6 Mod. 1 depth charge pistols and booster extenders, they should requisition Packing Nut and Gland Wrenches (Dwg. 180388-15) direct from either of the aforementioned depots, or the nearest issuing depot, without reference to the Bureau.

6. Those issuing depots which maintain a stock of the original type of service tool sets on hand for


See Change 4 at the end of the book.
 

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issue, or which utilize the Mark 2 Mod. 1 depth charge testing sets for testing pistols and extenders, are authorized to requisition sufficient packing nut and gland wrenches to make these sets applicable for use with Mark 6 Mod. 1 pistols and booster extenders direct from the Naval Mine Depot, Yorktown, or the Naval Ammunition Depot, Hawthorne. Additional wrenches may be requisitioned in order to maintain a reasonable surplus (not to exceed ten (10) for issue to vessels complying with paragraph 5 above).

7. The addition of the safety stop for depth setting wrench and the safe setting lock to both Mark 6 and Mark 6 Mod. 1 pistols requires that a pair of long nose pliers and a spool of No. 19 (".0358) dia. copper wire be issued for inclusion in the service tool set. The instructions noted in paragraph 5 for requisition of wrenches also apply for these items.

ASSEMBLY INSTRUCTIONS

8. Before assembling components to make up a complete depth charge, check each part to see that it bears a depot inspection tag or stencil. This marking insures that the particular component was in proper working order when shipped.

INSTALLATION OF BOOSTER AND BOOSTER EXTENDER

9. Install a booster and booster-extender in a depth charge case as follows:

(a) Engage the socket on the booster can with the collar on the booster-extender. Place the booster and booster-extender in the central tube of the depth charge case, with a rubber gasket, in good condition, between the booster-extender flange and the flange on the central tube.

(b) Place cap screws with lock washers in the flanges and tighten the screws gradually, one by one, until all are uniformly tight. If the screws are

 

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Depth setting mechanism with booster on top.

 

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not all tightened equally, the booster-extender may be slightly cocked in the central tube. This condition may cause faulty operation of the mechanism, or may allow water to leak into the central tube of the depth charge.

10. TEST the booster-extender as follows:

Spindle and extender testing tool.

(a) Remove the safety fork. (Hooking the extender testing tool into the eye of the fork is a convenient means of doing this). When the fork is removed the spindle should move inward about 1/4 inch due to the spring tension in the bellows. Only on rare occasions will the Mark 6 booster extender fail to do this. However, since the spindle of the Mark 6 Mod. 1 booster extender passes through a seal in the spindle bushing, the spindle will sometimes fail to move inward due to tightness of the seal. If the spindle does not move inward, the packing gland should be backed off to free the spindle. Approximately 1/4 turn should be sufficient to accomplish this purpose. In this connection it should be noted that the function of the gland seal is to prevent moisture entering the booster extender hydrostatic chamber when the safety fork is in place on the spindle. Excessive slackening of the packing gland will permit water to leak along the spindle into the hydrostatic chamber, causing corrosion and, at times freezing of internal operating parts.

(b) Engage the hook of the testing tool in the hole at the end of the spindle and pull outward. Hold the spindle in this position and swing the body of the tool until the recessed end engages in the

 

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groove in the spindle. Release the tension on the tool. The booster spindle will be retracted by the tension in the bellows and the body of the tool will be pulled into the hole in the spindle bushing. The hook will now be free ; swing it outward to clear the flange. Before releasing the tension on the tool be sure that it is well centered on the spindle so that the seal on the Mark 6 Mod. 1 booster will not be gouged with the edge of the tool as it is pulled into the hole.

(c) Test the booster for freedom of motion by pushing the spindle inward about 3/4 inch, ONLY.

(d) The spindle has a certain natural resistance to motion due to the reaction of the spring and friction of the locking balls. If there is binding or resistance in excess of this natural resistance and the cause cannot readily be found and corrected by examination of the booster can, central tube or exterior of extender mechanism, return the extender mechanism to a depot or tender for overhaul.

(e) To release the tool from the booster spindle, swing the hook into the hole at the end of the spindle. Pull outward on the hook and disengage the body of the tool from the groove. Swing the body of the tool outward and away from the spindle and replace the safety fork. Remove the hook.

INSTALLATION OF DETONATOR

11. To install a detonator in a pistol and to install the pistol in the case, proceed as follows:

(a) Remove the safety cover and inspect the ports of the inlet valve (Mark 6 pistol) or the orifice of the deep firing mechanism (Mark 6 Mod. 1. pistol.) Set the deep firing pointer at 0-300. Replace the safety cover.

 

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(b) Set the index pointer to SAFE with the depth setting wrench. (Check to see that the pistol is cocked. Then rotate the index pointer counterclockwise from "Safe" to "30" and clockwise from "30" to "Safe" with the depth setting wrench. An improperly assembled depth setting sleeve or a sheared index pointer stop pin can thus be discovered before the detonator is attached to the pistol and before the pistol is installed in the depth charge.)

(c) Release the detonator holder locking spring and remove the detonator holder with detonator holder wrench.

Locking spring (d) Place the detonator in the detonator collar. Lower the detonator holder over the detonator and with the detonator holder wrench screw it in place. Replace the detonator holder locking spring. See that the end of this spring projects inside of the guide tube to prevent the detonator holder from backing out.

Detenator

CAUTION: CAUTION: THE OPERATION OF ATTACHING THE DETONATOR TO THE PISTOL SHOULD BE PERFORMED WITH EXTREME CARE.

(e) Place a rubber gasket on the central tube

 

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flange of the depth charge case or slip the gasket over the centering flange of the pistol and hold it against the pistol carrying flange. Then insert the pistol in the case.

(f) Put securing cap screws and lock washers in place. Locate the safety stop for depth setting wrench by placing its attaching cap screws in the pistol carrying flange holes adjacent to the "150" and "250" dial marks. Note that the safety stop is provided with a marking on the top of the projecting mid-section to indicate its relationship to the center of the pistol. Set up the cap screws until all are uniformly tight.

(g) Make up the safe setting lock by reaving a piece of No. 19 (".0358 dia.) copper wire through the holes in the solid lug of the index pointer and the holes in the wrench safety stop. Use the long nose pliers and a piece of wire approximately 6 inches long for this purpose. Both of these items are included in the service tool set. If the depth charge is intended for immediate use the safe setting lock may be omitted at the discretion of the responsible officer.

LOADING DEPTH CHARGES INTO RELEASE TRACKS OR PROJECTORS

12. For instructions in loading depth charges into release tracks or projectors see O.P. No. 35, "Depth Charge Release Track, Mk. 1"; O.P. No. 721, "Depth Charge Release Tracks, Mk. 3"; O.P. No. 63, "Depth Charge Projector, Mk. 1"; or O.P. No. 831, "Depth Charge Projector, Mk. 6 Mod. 1" O.P. No. 904, "Depth Charge Release Gear," under preparation, will cover all types of depth charge tracks. It will supersede O.P.'s Nos. 35 and 721 when it is issued.


See Change 2, at end of book.
 

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REMOVING AND CHANGING SAFETY FORKS AND PISTOL COVERS

13. Plain (shipping) safety forks on booster-extenders and plain safety covers on pistols must be removed and replaced with knobbed safety devices after depth charges are loaded into release tracks.

14. A plain safety fork may be easily removed from a booster-extender by engaging the hook on the extender testing tool in the hole in the fork and pulling the fork clear of the spindle of the mechanism. After the fork is removed, the spindle will spring inward about 1/4-inch. The hook on the testing tool may be used to pull the spindle outward far enough to permit installation of the knobbed safety fork.

15. The plain cover on a pistol May be removed by unscrewing it from the inlet valve or the deep firing mechanism of the pistol. A knobbed cover is installed on the pistol by merely screwing it on firmly, in place of the plain cover. The safety cover is installed to keep the interior of the pistol mechanism dry. For this reason it should be firmly secured in place. However, a pipe wrench, pliers or other tool should not be applied to the knob for the purpose of screwing on the safety cover. A good grip with the thumb and forefinger applied at the rim of the cover will be sufficient to form a tight seal.

15 A. - Attached Sheets (Change 2)

16. When a depth charge is placed on a projector, the plain shipping fork and plain safety cover are to be left in place until immediately before the projector is fired. (It is intended that paragraph 19. of O.P. 831, July 1942, shall be revised in this respect.) The plain safety fork and plain safety covers remain in place while depth charges are in roller loaders.

 

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Depth setting dial, set at SAFE

 

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SETTING DEPTH ON PISTOL

17. Pistols should be set for the desired firing depths at a time prescribed by the Commanding Officer.

SETTING THE MARK 6 PISTOL

18. Set a Mk. 6 pistol as follows:

(a) Place the depth-setting wrench on the index pointer of the pistol, with the open section of the wrench fitted over the arrow on the pointer. Turn the pointer in a counterclockwise direction from SAFE to 30, or in a clockwise direction from 30 to SAFE.

(b) When setting the pointer in a counterclockwise direction to 30, do not attempt to force it past the 30 mark and against the stop pin. Likewise, when moving the pointer clockwise to SAFE, do not attempt to force the pointer past the SAFE mark and against the stop pin. The attachment of safety stop for the depth setting wrench is intended to prevent moving the index pointer beyond its limits. If this is done it may result in shearing off the index pointer stop pin. As a consequence, the proper relationship between the adjusting bushing and the depth-setting sleeve will be destroyed. And when the index pointer is subsequently rotated counterclockwise, the adjusting bushing will be forced against the hydrostatic piston to produce a highly unreliable depth setting or cause firing of the detonator during the setting operation.

 

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SETTING FOR LESS THAN 300 FEET
SETTING FOR LESS THAN 300 FEET

SETTING THE MARK 6 MODE 1

19. Set a Mk. 6 Mod. 1 pistol as follows:

(a) To set the pistol for a depth of 300 feet or less, remove the safety cover and see that the deep-firing mechanism pointer is set at the 0-to-300 mark on the inner dial. If it is not, set it by turning the pointer with a screwdriver (or the screwdriver end of the depth-setting wrench.) Replace the safety cover and set the outer pointer for the desired depth as directed in paragraph 18.

 

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SETTING FOR GREATER THAN 300 FEET
SETTING FOR GREATER THAN 300 FEET

(b) If the depth charge is to be set to fire at a depth greater than 300 feet, set the index pointer at the 100-foot mark on the outer scale. Remove the safety cover and turn the deep-firing mechanism pointer to the desired setting. Replace the safety cover.

 

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NOTE: The strength of the index pointer stop pin in the Mark 6 Mod. 1 pistol has been increased. However, instructions noted in paragraph 18(b) above must be observed.

The installation of a seal, between the dial plate and the neck of the depth setting sleeve to make this pistol watertight, increases the torque required on the depth setting wrench as compared with the Mark 6 pistol. Generally tightness at this point is a good assurance against leakage and should not cause concern as to the condition of the pistol. However, instances may occasionally be encountered where it is practically impossible to turn the index pointer. This may be caused by binding between the piston stem and the wall of the hole in the adjusting bushing. Pistols defective in this respect should be reconditioned.

Stern of ship showing release tracks and projectors.

 

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LAUNCHING O.P. NO. 747

DROPPING CHARGES FROM RELEASE TRACKS

20. After a depth charge is properly installed in a release track, with a knobbed safety fork on the booster-extender and a knobbed safety cover on the pistol, no other operation is necessary before dropping the charge other than setting the pistol for the desired depth.

THROWING CHARGES FROM PROJECTORS

21. Immediately before firing a projector, pull the safety fork from the booster-extender with the attached lanyard and unscrew the safety cover from the inlet valve or deep-firing mechanism of the pistol.

UNDERWATER ACTION
SINKING RATES OF DEPTH CHARGES

22. The combined case and charge components of the depth charges described in this pamphlet are symmetrically loaded cylinders and have no stabilization of tumbling, spiral, and leafing actions which are aggravated by the initial disturbance of the ship's wake. In order to facilitate production, a tolerance must be allowed on the pressure at which pistols are required to fire at specific depth settings. These circumstances result in some variation of explosion times at all depth settings. The variations increase in proportion to the depth at which the pistols fire and may be expected with both the Mark 6 and Mark 6 Mod. 1 pistol.

23. In tests at sea, specially calibrated Mark 6 Mod. 1 pistols installed in Mark 6 and Mark 7 depth charges were dropped from different type ships at varying speeds. The time elapsed from the moment

 

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each charge struck the water until the explosion was felt on deck was clocked with three or more stop watches. The sinking data thus obtained was compiled and analyzed mathematically and a mean sinking rate was determined. Still water tests have also been made in tanks and lakes but are not considered to reflect true conditions, particularly with respect to the unweighted "ash can" depth charge.

24. The results of tests to date are as follows:

For destroyer class ships:

Depth
Charge
Time to
50 ft.
(sec.)
Time to
100 ft.
(sec.)
Time for each
succeeding
100 ft.
(sec.)
Mark 6 10 16 12.2
Mark 7 10 16 11.1

For small types of vessels such as mine sweepers, SC's, etc:

Depth
Charge
Time to
50 ft.
(sec.)
Time to
100 ft.
(sec.)
Time for each
succeeding
100 ft.
(sec.)
Mark 6 7.5 13.5 12.2
Mark 7 7.5 13.5 11.1

25. Mark 6 depth charges with arbors attached, due to initial entrance velocity, sink to 50 feet in about 5 seconds, thereafter the sinking rate is about 9.5 ft./sec.

26. The sinking rates noted herein for large and small anti-submarine vessels are considered to be the high limits.

 

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The restricted clearances required in the depth setting mechanism for deep firing of the Mark 6 Mod. 1 pistol have made it difficult to obtain firing within close limits of the 30 ft., 50 ft. and 75 ft. index pointer settings Tests, in still water, of this pistol installed in a Mark 6 depth charge indicate the following:

Depth
Setting
(ft.)
Firing
Depth
(ft.)
Max. Min. Ave.
30 65 61 63
50 79 67 72
75 98 85 92

28. The firing depths noted may be expected to show a closer approach to respective depth settings when the depth charge is dropped in disturbed water under service conditions.

29. Delayed firing may be expected when charges fitted with Mark 6 Mod. 1 pistols, set at 30 feet, are dropped in shallow water. In this connection it should be noted that the pressure required to fire both Mark 6 and Mark 6 Mod. 1 pistols at the 30 foot setting is 10 to 15 psi. This pressure is equivalent to 22 to 40 feet depth of sea water.

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