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APPENDIX I

Adjustment of Indirect Fire by Sound

Section I. GENERAL


To effectively use indirect firepower, it is sometimes necessary to adjust fire, and in a jungle environment this requires special techniques. In the limited visibility of the jungle, the only method available for adjustment may be by the sound of the explosion of the round. The techniques described are equally effective in the adjustment of artillery or mortars.

The basic principle of adjustment by sound is that the direction and distance to the target are known, and the direction and distance to the explosion of the round can be calculated from the sound of the explosion. These data are compared to determine the appropriate correction in deviation and in range. The problem encountered in this method is that the heavy foliage distorts sound and makes it difficult to determine range or lateral shift corrections. There is a distinct technique used to determine the correction in each of the two dimensions.

CONTENTS

SECTION

  I. General

 II. Techniques Used to Determine Corrections

III. Other Considerations

Section II. TECHNIQUES USED TO DETERMINE CORRECTIONS


CORRECTION IN DEVIATION

The direction from the observer to the target is measured from a map or by compass. The direction to the explosion is measured with a compass. These two azimuths, expressed in roils, form an angle as illustrated.

CORRECTION IN RANGE

The distance from the observer to the target can be measured on a map or can be estimated. The distance to the explosion of the round is calculated by counting the number of seconds from the impact of the projectile until the observer hears the explosion. Multiply the number of seconds by the speed of sound, 350 meters/second. Add or drop the resulting distance, as appropriate.

To tell the observer when the round impacts, the fire direction center (DFC) provides "splash and count." In splash and count, the FDC sends, "Splash -four, three, two, one-impact." On the word "impact" the round lands, and the observer starts counting the seconds until he hears the explosion.

Section III. OTHER CONSIDERATIONS


The FDC normally does not send "splash and count"; rather, it must be requested in the call for fire by saying, "Cannot observe - splash and count."

Many times in dense jungle terrain, a round's effect is lost in the trees. Delay fuze can be used to penetrate the foilage and put the desired effects on the ground. A combination of fuze quick and fuze delay can be effective.



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