In both cases they were sure that great difficulties
in production would meet our attempts at retaliation.
In general this proved true, but in this case and increasingly
throughout the war, they reckoned without Allied adaptability.
The French development of phosgene manufacture was indeed remarkable.

Very interesting light is thrown on this attack by Major Barley,
D.S.O., Chemical Adviser to the British Second Army. It appears that
in November, 1915, the French captured a prisoner who had attended a gas
school in one of the factories of the I.G. Here lecturers explained
that a new gas was to be used against the British forces, many thousands
of casualties were expected, and an attack would follow, which,
correcting the errors of the effort at Ypres, would lead to the capture
of the Channel ports. Efforts were at once made to obtain information
on gas preparation by the Germans in front of the British sectors.
In this way a sergeant-major was captured on the morning of December 16th,
and he revealed the date and front on which the cylinders were installed.
About 35,000 British troops were found to be in the direct line of the gas,
but owing to the timely warning and to the protection which had recently
been adopted, we experienced very few casualties. The Germans had prepared
a huge infantry attack, and used a new type of gas shell on this occasion.
German troops massing must have received huge casualties owing to our
preparation and the failure of their gas attack.

The last German cloud attack on the British front occurred on August 8, 1916.
There were later attacks against the French, but the Germans were replacing
the cloud method by other methods which they considered more suitable.
These will be discussed later on, when considering our own reaction against
the chemical offensive.