OCR Text |
Show I Atn - - Nai Ur'" Ufa mm nX UNDERWOOD " " w-v , " zarcZZ cSAfTJ GZAT Gfflf5 OWN at the Coast Artillery f school at Fort Monroe, Va.. Uncle Sam Is turning out the latest pattern of modern mod-ern heavy artillery officers. The National Guard coast )! aiH artillery officers and such Jpu)JJjj of the regular establish-(ffltKTVA establish-(ffltKTVA ment as have not yet been (Xymjj v through this school have MlTiMml'J been ordered down in two sections, the first df -which already has been graduated. Upon the Coast Artillery corps has been thrust the burden of handling the heavy ordnance with which the army is equipped, and which in the field will be manipulated by methods meth-ods more or less resembling the methods meth-ods already laid down for sea coast ordnance. These methods lire far different from those used by the field artillery proper that is, the light three-inch rifles and 4.7-inch howitzers. The present-day heavy artillery officer offi-cer must be a mathematical shark, a railroad engineer and an expert in handling gasoline motors, besides having hav-ing an intimate knowledge of gunnery, gun-nery, says a writer in the New York Herald. His equipment has changed from the battery commander's ruler of the field artilleryman to a lide rule, a transit and a book of logarithms. In addition he must understand perfectly per-fectly the manipulation of heavy masses termed the art of mechanical maneuvers for his guns will not be securely emplaced in concrete, but will be exposed to the mercies of the open road, with conserpient overturn-ings overturn-ings and sudden shlftings. He must know how to use tackle of all sorts, and in general know all the tricks of the modern contractor. The officers who carne down to Fort Monroe were nearly all graduates of the National Guard courses prescribed by the war department and were fully competent to handle seaconst .ordnance In the forts to which they were assigned. as-signed. They thought that their knowledge was ample, and it would have been for this work, perhaps, hut after a day or so they foimfl out that while this knowledge was essential to them as basic, it was only the beginning. be-ginning. Gunnery the Big Thing. The big thing, of course, was gunnery. gun-nery. Tills included a practical knowledge knowl-edge of ballistics the science of the movement of bodies through the air. Ballistics is a very exact science, and In these days of precision is absolutely absolute-ly essential for the artilleryman. Reduced Re-duced tc language for the layman, ;it consists in the knowledge of'Jnst how-far how-far a given piece of ordnance will hui'l Its projectile under all conditions. 'Very simple, say you. Yes, under standard conditions. Every gun when It is turned out from the maker Is known to fire a certain projectile to a et-rtain range at a certain elevation. These data are complied in tables and are theoretically the same for all gum of the same caliber and model. These tables are known as range tables, anil the conditions given for the firing of projectiles for these theoretical ranges are 'known as range table conditions. Remember this. Now some of the principal range table conditions or assumptions are that the earth is flat and does not revolve- that the atmospheric conditions condi-tions are standard ; that there Is no wind : that the gun and target are on the same level, and that the action of gravity Js constant throughout the trajectory. All well and good. We know that our gun, then, will fire its projectile, let us say 10,000 yarfis, under range table conditions. In other words, given the above conditions, H will, if prop- i perly laid in direction, ihit a target 10,000 yards away. But unfortunate- ; ly for us the earth Is not fiat, our tar- i get Is 10,000 yards away, atd 200 feet above the level of the gun there is a ten-mile wind blowing straight across the line gun target, the thermometer Is up to 85 and the barometer has dropped to 29. Will the projectile hit the target now? Not unless you correct cor-rect the elevation of the gun for some of these conditions and Its laying for the others. How are you going to do it? First, you must find the force with which your projectile cleaves the air. This Is called the ballistic co-efficient, and Is reduced by a simple formula to a figure. Knowing the weight of the projectile, its form and its diameter the ballistic co-efHcient is easily calculated, cal-culated, r The Air as a Check. V You have now taken the first step. You have the force of projectile to penetrate the atmosphere under standard stand-ard conditions. But this force varies I with the atmosphere. On a heavy, muggy day the atmosphere is dense, and you will be surprised the checking check-ing effect it will have on your projectile. projec-tile. By means of elaborate tables one can find just what this effect is, and we apply it to the original formula. Also in the atmospheric factor Is Included In-cluded the temperature, for In hot weather our powder charge when Ignited Ig-nited exerts more strength in decomposing decom-posing Into gases than it does on a cold day. So far so good. What about this troublesome wind that is blowing? If it blows against the projectile it checks lt ; if with it, it helps it along. So we have two varying factors, which the ballistlcian juggles by utilizing utiliz-ing trigonometry until he gets them in terms where he can once more change his ballistic co-efficient, making It larger or smaller as the wind Impedes Im-pedes or accelerates the projectile. Not quite so easy as you thought, is it? But we are not through yet. We know that under range table conditions our propelling charge has a force that gives the projectile an initial velocity of so many foot seconds, sec-onds, say 2,250. But our powder has been stored la a dugout whose temperature tem-perature is not normal, so by more figuring fig-uring we find out just what this real velocity for the day is. Now we can hegin to figure what elevation the gun must have to travel that 10,000-yard 10,000-yard path to the target. By dividing our old friend C, as the ballistic co-efficient Is termed, by the distance in feet, that the projectile must travel, we get a reference number. num-ber. This number we take with us and bury our noses In more tables until un-til we find opposite this number In a column headed by the muzzle velocity another number. This number, multiplied multi-plied by C again, gives us the sine of twice the angle of .departure. A quick glance into a table of logarithmic logarith-mic sipes gives this to us, and dividing by two we have a figure in degrees and minutes that represents the angle which the gun must be elevated from the 'horizontal to send its projectile 10,000 yards today. AValt a minute. Our target is 200 feet above the level of the gun. Also because of the curvature curv-ature of the earth this 200 feet height lias been reduced somewhat. So once more we delve Into mathematics to correct cor-rect the curvature of the earth and hel?it .of site of the target. The result re-sult we subtract from the angle found, and tlits time our gun is ready for business. Is Mr? No ; it Is not so 'easy. The Influence of the Rifling. Every rifled jiiece of ordnance imparts im-parts a twist to Its projectile, and this twist causes the projectile to deviate devi-ate from its course. In our service this deviation, called drift, is to the right, and is In ratio with fibe range. It Is constant, therefore, for each range, and we find It very easily, either by math-ematlc math-ematlc computation or from drift tables. ta-bles. Also we go back to our wind problem and find hat effect the wind will have in pushing the projectile from its course, either to the right or left. . These two corrections are brought together and determine the amount in degrees and minutes that the muzzle of the gun must be shifted shift-ed from the target to the right or left In order that the projectile will curve toward its goal. At last we have our gun controlled so that lt will hit the target. Tarry just a moment. A gun, the text books tell us, Is the simplest form of gas engine. Did you ever know tiro' gas engines of the. same model that acted alike? Neither will two guns of the same model. The Fifty Per Cent Zone. Tf you have an automobile you know that the piston rings wear out, allowing allow-ing gases to escape, and thus reducing the force with which the piston Is forced down. Also the cylinder becomes be-comes scored with the same result. Now, if you fire your gun many times the same tiling happens. The projectile projec-tile is the piston and the retaining band of copper the piston ring that seals the bore. If the bore is eroded or if the rotating bands are not perfect per-fect a certain escape of gases occurs and the flight of the projectile is consequently con-sequently affected. Again, there may be a difference In the weight of powder charges or in the weight of file projectiles, which will give slight variations in the flight of the projectiles. So that the battery commander must know the dispersion of each piece. This he finds out from observation of his shots, and It changes as the gun grows older. By figuring the deviation of a certain group of projectiles from the target, and wliich are known as trial shots or fire for adjustment, he finds out what is known as the mean error of the gun. This, multiplied by the factor .845, well known to students of probabilities, prob-abilities, gives the mean probable error. er-ror. Multiplying by two, the result in yards is what is known as the 50 per cent zone, within which W per cent of his projectiles will fall. This computation compu-tation is done longitudinally and latl-tudinally, latl-tudinally, giving a certain oblong strip. If the center of this strip can be placed on the target by observation of fire the battery commander has done all that he can, and may now open fire for effect. Four times the 50 per cent zone gives the 100 per cent zone, within which practically all his shots -will fall. Knowledge of these zones is all Important. Im-portant. By this means he can figure out how near he can come to our own first line trenches without murdering our infantry, and, what is almost as Important, when lt Is necessary to save ammunition he can easily compute how many shots will be necessary to make a certain number of hits on a given target. And what about camouflage? The enemy airplanes are on the alert and all gun positions must he disguised. The battery commander must be a master of camouflage, able to erect shelters and under their cover to build his emplacements, while by the exercise exer-cise of discipline he restrains his men from making tracks about the positions posi-tions which will give away to the all-seeing all-seeing eye of the camera In the air the fact that guns are mounted there. So that is why the student officers at Fort Monroe blistered their hands and strained their backs erect-liig, erect-liig, camouflages and digging dugouts and bombproofs; that is why they dove and crawled under motortrucks and delved into differentials and gear cases, emerging dirty and grimy, but happy ; that is why they toiled for hours at night, working out lengthy problems in trigonometry until angles danced before their eyes when they tried to sleep and endless chains of logarithms curved themselves through their brain cells. |