522 



SCIENCE 



[N. S. Vol. XLIX. No. 1274 



methods of observation designed to avoid con- 

 fusion in oi)eration on a very active front. The 

 Germans had an extremely efficient flash rang- 

 ing service, many of the good features of 

 which were copied by the Allies as they became 

 known through captured documents. The 

 flash ranging reported not only the positions 

 and activity of hostile batteries, but also the 

 exact locations of other enemy objectives such 

 as traffic on roads, troop movements, jmsition of 

 observation balloons, etc. Being provided with 

 high-power telescopes, and since observation 

 was obtained from stations on a wide base 

 (from flve to eight miles) the flash ranging sec- 

 tions were particularly well suited for obser- 

 vation and ranging in the enemy back areas, 

 and these sections rendered invaluable services 

 both to the artillery and to the army intelli- 

 gence. 



A battalion of five companies (74th Engi- 

 neers) furnished the ranging troops for an 

 American army. A sound ranging section 

 was in the field with the first American division 

 to enter the line (March, 1&18) and on the 

 signing of the armistice the entire front of the 

 second American army was covered with both 

 flash and sound ranging sections and a portion 

 of that of the first American army was covered 

 by flash ranging, although the ranging battal- 

 ion allotted to this army had not yet arrived 

 in France. The ranging service was thus a 

 " going concern " from the very first and was 

 not one of the many which could have delivered 

 results had the war but lasted a little longer. 



A flash ranging section consisted of about 

 one hundred men commanded by a lieutenant 

 who was assisted by three other officers and by 

 an exceptionally high grade of non-commis- 

 sioned officers and men, all of whom had been 

 given a month's intensive training in France. 

 The instruments and methods employed were 

 those suited for accurate survey and present no 

 special features of interest. 



A soujid ranging section was similar in or- 

 ganization to the flash section except that there 

 were fewer enlisted men (60-YO) due to the 

 fact that instrimients took the place of living 

 observers to a great extent. The " central " in- 

 strument recorded photographically the time of 



arrival of the sound of the enemy guns at a 

 series of instruments at surveyed jwsitions 

 near the front line and covering a length of 

 about five miles; this instrument delivered au- 

 tomatically developed and fixed photographic 

 records in less than a minute after the sound 

 of the enemy gun reached the front line and 

 this record could be interpreted by the use of 

 quick graphical methods so that the position of 

 the enemy gun could be telephoned to the 

 friendly artillery in about a minute more. The 

 probable accuracy of the location could be 

 given and also the caliber and target of the 

 piece which had just fibred. The service was 

 not interfered with by rain or fog or darkness, 

 though it was rendered less accurate by strong 

 winds. Calculations were rendered difficult by 

 great artillery activity though not impossible 

 except under actual " barrage " conditions. 



In ranging the friendly artillery on enemy 

 objectives it was i)ossible to range all the guns 

 of the battery simultaneously, thus effecting 

 considerable time saving over other methods of 

 ranging. If the ranging was being done on an 

 enemy battery which had just fired the accu- 

 racy attained was very great (less than twenty- 

 five yards), because of the fact that in this 

 case no wind or temperature corrections need 

 be applied in the calculations. 



After the American advances of September 

 and !N'ovember a careful survey was made of 

 most of the enemy positions which had been 

 located by either the sound or the flash ranging 

 sections on a part of the American front ; the 

 result of this survey was that of the locations 

 of the flash ranging about one third were accu- 

 rate to within fifty yards, another third to 

 within one hundred yards and the other third 

 with errors of more than one hundred yards. 

 In the first third were many extremely accu- 

 rate locations of guns the positions of which 

 were visible from two or more observation 

 posts; in the last third were mostly locations of 

 concealed heavy caliber distant guns generally 

 more easily located by sound ranging, whose 

 positions could only be inferred from smoke 

 puffs by day or flares in the sky by night. 



The survey showed that the estimates of 

 accuracy made by the soimd rangers in report- 



