Page:EB1911 - Volume 02.djvu/736

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in this case, as also when the guns are under cover or engaging a target under cover, an “aiming point” or “auxiliary mark,” a conspicuous point quite apart and distinct from the target, has to be employed (“indirect” method). In the Russo-Japanese War the sun was sometimes used as an aiming point. When the guns are behind cover and the foreground cannot be seen, an artificial aiming point is often made by placing a line of “aiming posts” in the ground. If an aiming point can be found which is in line with the target, as would be the case when aiming posts are laid out, the laying is simple, but it is as often as not out of the line. Finding the “line” in this case involves the calculation, from a distant observing point, of the angle at which the guns must be laid in order that, when the sights are directed upon the aiming point, the shell will strike the target. It is further necessary to find the “angle of sight” or inclination of the line of sight to the horizontal plane. If aim be taken over the open sights at the target, the line of sight naturally passes through the target, but in any other case it may be above or below it. Then the point where the projectile will meet the line of sight, which should coincide with the target, is beyond it if the line of sight is below or angle of sight is too small, and short of it if the line of sight is too high—that is, range and fuze will be wrong. The process of indirect laying for elevation therefore is, first, the measurement of the angle of sight, and secondly, the setting of the sights to that angle by means of a clinometer; this is called clinometer laying. In all cases the actual elevation of the gun to enable the shell to strike the target is a purely mechanical adjustment, performed independently; the gun is moved relatively to the sights, which have been previously set as described. Frequently the battery commander directs the guns from a point at some distance, communication being maintained by signallers or by field telephone. This is the normal procedure when the guns are firing from cover. Instruments of precision and careful calculations are, of course, required to fight a battery in this manner, many allowances having to be made for the differences in height, distance and angle between the position of the battery commander and that of the guns.

29. Ranging[1] (except on the French system alluded to below) is, first, finding the range (i.e. elevation required), and secondly, correcting the standard length of fuze for that range in accordance with the circumstances of each case. To find the elevation required, it is necessary to observe the bursts of shells “on graze” with reference to the target. The battery commander orders two elevations differing by 300 yds., e.g. “2500, 2800,” and tells off a “ranging section” of two guns. These proceed to fire percussion shrapnel at the two different elevations, in order to obtain bursts “over” (+) and “short” (−). When it is certain that this “long bracket” is obtained, the “100 yds. bracket” is found, the elevations in the given case being, perhaps, 2600 and 2700 yds. “Verifying” rounds are then fired, to make certain of the 100 yds. bracket. The old “short bracket” (50 yds.) is not now required except at standing targets. Circumstances may, of course, shorten the process; for instance, a hit upon the target itself could be “verified” at once. The determination of the fuze (by time shrapnel) follows. The fuze has a standard length for the ascertained range, but the proper correction of this standard length to suit the atmospheric conditions has to be made. The commander has therefore already given out a series of corrector[2] lengths, his object being to secure bursts both in air and on graze. When he is finally satisfied he opens fire “for effect.”

30. An example of the ordinary method of ranging, adapted from Field Artillery Training, 1906, is given below.

Battery commander gives target, &c., and orders: “Right section ranging section; remainder corrector 150 increase 10, 4400-4700,” for the long bracket.

No. 1 gun fires, elevation 4400 yds., P.S., round observed −

No. 2 gun fires, elevation 4700 yds., P.S., round observed +

B.C. orders “4500-4600.”

No. 1 gun fires, elevation 4500 yds., P.S., round observed −

No. 2 gun fires, elevation 4600 yds., P.S., round observed +

The 100 yds. bracket appears to be 4500-4600. B.C. orders: “Remainder 4500 time shrapnel,” and gives the ranging section 4500-4600 to “verify.” Guns 3, 4, 5, 6 set fuzes for 4500 with correctors 150, 160, 170, 180.

No. 1 gun fires, elevation 4500 yds., P.S., round observed −

No. 2 gun fires, elevation 4600 yds., P.S., round observed +

B.C. orders: “Remainder 4500, one round gun fire, 3 seconds.”

No. 3 elevation 4500 yds. T.S. corrector 150 air     

No. 4 elevation 4500 yds. T.S. corrector 160 air     

No. 5 elevation 4500 yds. T.S. corrector 170 graze

No. 6 elevation 4500 yds. T.S. corrector 180 graze

B.C. selects corrector 160 and goes to “section fire.”

The battery now begins to fire “for effect.”

No. 1 elevation 4500 yds. T.S. corrector 160 air     

No. 3 elevation 4500 yds. T.S. corrector 160 air     

followed by Nos. 5, 2, 4 and 6.

There is another method of ranging, viz. with time shrapnel only. In this the principle is that several shells, fired with the same corrector setting, but at different elevations, will burst in air at different points along one line. Bursts high in the air cannot be judged, and it is therefore necessary to bring down the line of bursts to the target, so that the bursts in air appear directly in front or directly in rear of it. Rounds are therefore fired (in pairs owing to possible imperfections in the fuzes) to ascertain the corrector which gives the best line of observation. This found, the target is bracketed by bursts low in the air observed + and −, as in the ordinary method with percussion shrapnel.

The operations of finding the “line of fire” and the proper elevation may be combined, as the shells in ranging can be made to “bracket” for direction as well as for elevation. The line can be changed towards a new target in any kind of direct and indirect laying, in the latter case by observing the angle made with it by the original line of fire and giving deflection to the guns accordingly. Further, the fire of several dispersed batteries may be concentrated, distributed, or “switched” from one target to another on a wide front, at the will of the commander.

31. Observation of Fire, on the accuracy of which depends the success of ranging, may be done either by the battery commander himself or by a special “observing” party. In either case the shooting is carefully observed throughout, and corrections ordered at any time, whether during the process of ranging or during fire for effect. The difficulties of observation vary considerably with the ground, &c., for instance, the light may be so bad that the target can hardly be seen, or again, if there be a hollow in front of the target, a shell may burst in it so far below that the smoke appears thin, the round being then judged “over” instead of “short.” On the other hand, a hollow behind the target may cause a round to be lost altogether. Ranging with time shrapnel has the merit of avoiding most of these “traps.” The “French system of fire discipline,” referred to below, has this method as the usual procedure.

32. Fire.—Field Artillery ranges are classed in the British service as: “distant,” 6000 to 4500 yds.; “long,” 4500 to 3500; “effective,” 3500 to 2000: and “decisive,” 2000 and

  1. Finding the line is also an integral part of ranging. When an aiming point is used, the angle at which the guns must be laid with reference to it is calculated and given out by the battery commander. The modern goniometric sight permits of a wide angle (in England 180° right or left) being given. “Deflection” is a small angular correction applied to individual guns.
  2. The “corrector” is an adjustment on the sights of the gun used to determine the correct fuze. In the British Q.F. equipment, a graduated dial or drum shows the elevation of the gun above the line of sight. The fuze lengths are marked on a movable scale opposite the range graduations to which they apply, and the “corrector” moves this fuze scale so as to bring different fuze lengths opposite the range graduation. For example, a certain corrector setting gives 11½ on the fuze scale opposite 4000 yds. on the range scale, and if the shells set to 11½ burst too high, a new corrector setting is taken, the fuze length 12 is now opposite to the 4000 range graduation, and this length gives bursts closer up and lower. In the German service a corrector (Aufsatzschieber) alters the real elevation given to the gun, so that while throughout the battery all guns have the same (nominal or ordered) elevation shown on the sights, the real elevations of individual guns vary according to the different corrector settings. Thus bursts at different heights and distances from the target are obtained by shifting the trajectory of the shell. The fuze, being set for the nominal elevation common to all the guns, burns for the same time in each case, and thus the burst will be lower and closer to the target with a less (real) elevation, and higher and farther from it with a greater.