METHODS OF GAS WARFARE 65 



up to find protection against it. The outcome was a hel- 

 met saturated with sodium phenate. The concentration 

 of gases when used in a cloud is small, and I to 1,000 by 

 volume is relatively very strong. The helmet easily gave 

 protection against phosgene at a normal concentration of 

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

 attack came in Flanders, on the I9th 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 war- 

 fare, and these were all emphasized in the attack of De- 

 cember. They are: (i) increased concentration; (2) 

 surprise in tactics; (3) the use of unexpected new ma- 

 terials. 



Continued efforts have been made on both sides to in- 

 crease 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 real- 

 ized 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 doubled 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 be- 

 tween dawn and sunrise. Gas attacks have therefore 

 been frequently made just in the gloaming or early morn- 

 ing, between lights. This took away one of the easy 

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



