GUN LOCATION

Dominion, Volume 12, Issue 267, 7 August 1919, Page 5

GUN LOCATION

SCIENCE ON THE BATTLEFIELD

LECTURE BY PROFESSOR E. MARSDEN

"Gun Location on tho Western Front" wa*s tho subject of a lecture pen by Major' B. Marsden, M.C. (Professor of Physics, Victoria College), ln-fore tho Wellington Philosophical Society last night. Major Marsden, while on active servico, was engaged in 'Uo location of Gorman guns and other rangc-l'iuling operations by the most modern scientific mothods.

Major Marsden said his subject was the location of Gel-man guns by field 6urvoy methods, as distinct lioni aeroplane observation. The \vo chief methods wero flash spotting .:iid sound ranging. Tho maps available m tho early part of the war .were very accurate in detail, but wore not adequate for modern artillery methods. The jiriUsh had some good maps of Belgium to start with, and used French and Belgian maps as tho bases of larger and more detailed nibps, ruled in distance squares. Sonic- of tiie later maps were on a seaio of six ir.ches to the mile and wero accurate to two or three yards as far as they ivere marked. Major Marsden produced samples of maps of various types, maps • painted at the front for use in big attacks, and the daily map'', showing location and position of eii-mly dnisions, issued for 6taff use. The counltr-bnt-tery maps, on a scale of. three inches to the mile, showed tho positions of all enemy batteries that had been located. Each battery luul a name, and if .the aeroplane observers reported tint it was active immediate steps iveie taken to "neutralise" it. When a. big attack was arranged, the counter-battery maps were 'used to enable the British guns to prevent the-. German guns getting effectively into action. Gunnery in these days demanded a great deal of technical knowledge. In the case of "Big Bertha," whicn bombarded Paris from a range of ninety miles, it had been said that the gunners had to make an allowance of about half a mile for the rotation of the earth whilo the projectile was in the air. Ordinary gunners had to deal with such complications as the finding of invisible works over known distances by means of maps that had three norths—true north, magnetic north, and "quid" north. Tho "quid" lines on the map, arranged in 1000-yard squares', were not absolutely, true to north owing to the difficulties of projecting the curved surface of the earth on to a flat map. Major Marsden described the methods of range-finding by triangulation. The observation groups were stationed at carefully located positions, and they had to make exact observations and most coinplicated calculations. The factors included the "drift" of tlw shell, windage, wear of guns, and variations in ammunition. Air-burst spotting was one of the newer methods of adjusting ranges. The gunner exploded nis shell at a selected point in tno air, and from the data so supplied, tho observation groups calculated the ranges. The use of Very lights to'inform .observers of tho position of advancing troops was a phase of air-burst spotting. The lights were fired into the air from pistols, and the observers, by day.or night, could calculate the positions of the lights to within a few yards by triangulation. This method could be applied to bush survey. Sound ranging was effected by means of microphones, wHch caught tho report of a gun from points separated by-"perhaps 1400 yards. The speed at which sound travelled being known, the difference between the time recorded at one point and the time at the other point enabled the observer to plot „ the bearing of the gun. Several ■jiaira of microphones would be used to locate the gun, and accuracy to within .fifty yards over large ranges could be secured. The Germans and the French had methods of srund'ranging at the outset of the war, but a. British scientist, without much enefuracemenf from the gunners of the old sohool.j'had evolved in the' field a met'nod bv June, 1915. The problem was complicated by the fact that tho shell, tiavelling faster than sound, created a sound of its owr. sufficient to disturb the ordinary microphone and interfore with the recording of tho gun report. The British scientist, Mr. Bragge, evolved a ni'croDhone that would record both the sounds, and that was very sensitive to tbo sound of big guns, but took no notice of riflo bullets. It was an electrical dovice usod subsequently for the detection and location of aeroplanes. Major-Mars-den showed photographs of sound-rang-i.ift apparatus. The appliance, when connected with half a dozen recording instruments bohind tho line, would produce automatically a photographic record, onabliwr the officer in charge to calculate ihe position of tho gun under observation. The apparatus was set in operation bv an officer occupying a forward position. This officer pressed a key when he heard the report, two or three seconds before the souna reached the instruments, And so 6ot the apparatus in motion. > The position of a gun could be calculated in Uuee or four minutes aftor the instrument, had recorded the sound from three or mori- points. The readimrs had to be'corrected slightly for air ti-nvnerature both these factors interfering with the velocity of sound. The record, of the sound of the enemy pun could bo used to correct the range of a British gun firing at tho enemy batten'. Corrections by this method could Lo given to w-jthin a few yards without any visible observation at all. Tho development of suoh scientific methods explained why in one month of 1918 18 per cent, of the German guns on tho Western front were knocked out by countor-battery work. At tho Battle, of Arras the ranging offioerb had the locations of 97 per cent, of che German guns, and when the. British troops advanced only one enemy battery was able to fire cm them. The other German guns were kept silent by British fire. Major Mars. den mentioned that in the later stages of the war tho German commanders issued orders that tiheir i(unß imi6t not fire except in groups, in order to defeat the British 6ound-ranging instruments. But the instruments would record eaoh gun even when several were fired together. Tho sound-ranging sections did very good work even when mobile v/arfaro had been resumed and the Germans were giving ground. Major Marsden mentioned that the Australian success at Viilcrs Brotonneaus had been due to some extent to exact knowledge of German gun positions secured by a British sound-ranging section, 1 which had been lent to the Fi-enoh Army occupying the area before the Australian attack. The speed of sound had been determined more accurately than ever before by tfio apparatus evolved for war purpose*. Similar apparatus was used to locate torpedo explosions at sea. Major Marsden answered several questions. The officers and computers of the ranging sections were usually university mon, the work being highly technical. ! The trained man came to'tho fore. The lecturer, who had n large audience, was accorded a hearty vote o, 1 thanks.