auld: methods of gas warfare 49 



The outcome was a helmet saturated with sodium phenate. The 

 concentration of gases when used in a cloud is small, and 1 to 

 1000 by volume is relatively very strong. The helmet easily 

 gave protection against phosgene at a normal concentration of 

 1 part in 10,000. That helmet was used when the next attack 

 cahie in Flanders, on the 19th of December. This attack was 

 in many ways an entirely new departure and marked a new 

 era in gas warfare. 



There are three things that really matter in gas warfare, and 

 these were all emphasized in the attack of December. They 

 are: (1) increased concentration; (2) surprise in tactics; (3) the 

 use of unexpected new materials. 



Continued efforts have been made on both sides to increase 

 the concentration. The first gas attack, in April, 1915, lasted 

 about one and a half hours. The attack in May lasted three 

 hours. The attack in December was over in thirty minutes. 

 Thus, assuming the number of cylinders to be the same (one 

 cylinder for every meter of front in which they were operating), 

 the last attack realized just three times the concentration of 

 the first, and six times the concentration obtained in May. 

 Other cloud gas attacks followed, and the time was steadily 

 reduced; the last attacks gave only ten to fifteen minutes for 

 each discharge. We believe that the cylinders are now put in 

 at the rate of three for every two meters of front, and may even 

 be double banked. 



The element of surprise came in an attack by night. The 

 meteorological conditions are much better at night than during 

 the day. The best two hours out of the twenty-four, when 

 steady and downward currents exist, are the hour between 

 sunset and dark and the hour between dawn and sunrise. Gas 

 attacks have therefore been frequently made just in the gloam- 

 ing or early morning, between lights. This took away one of 

 the easy methods of spotting gas, that of seeing it, and we had 

 to depend upon the hissing noises made by the escaping gas, and 

 upon the sense of smell. 



Another element of surprise was the sending out of more 

 than one cloud in an attack. After the first cloud the men 



