LAUNCHING

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 opera-tion is necessary before dropping the charge other than setting the pistol for the desired depth.

THROWING CHARGES FROM PROJECTORS

21. Immediately before fring 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 pis-tols 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 types ships at varying speeds. The time elapsed from the moment 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 complied and analyzed mathematically and a mean sinking rate was determined. Still wa-ter 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 test to date are as follwos:

For destroyer class ships:

Mark 7

10

16

11.1

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

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 consi-dered to the high limits.

The restricted clearance required in the depth setting mechanism for deep firing of the Mark 6 Mod. 1 pistol have made it difficult to obatin 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:

Firing Depth (ft.)

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

29. Delayed fring 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 settings is 10 to 15 psi. This pressure is equivalent to 22 to 40 feet depth of sea water.