were again approached in the first German use of mustard gas.
The most telling examples will probably be found in the future,
unless the correct precautions are taken. The whole history of
chemical warfare during the war was a struggle for this initiative,
a struggle between gas protection and aggression.

Standard Uses for Gas;--Gas Shell.--But gas found an important
use besides that of strategic surprise. It became a standard
weapon for certain clear and definite tactical purposes.
(For some of these, indeed, the factor of local surprise
was important.) We refer to the specific use of gas shell
for the neutralisation of batteries, roads, and areas, and to
the use of cloud gas, prior to offensives for the production
of casualties, and wearing down of reserves. The Ypres attack
had not by any means established the use of gas for such purposes.
There is no doubt that, from this point of view, the experimental
period carried on for many months. Naturally, in some respects,
there was always an experimental element in the use of gas.

Further German Cloud Attacks.--Two days after the first cloud
gas attack the Germans launched a second against the Canadians,
with similar results. Quoting from official despatches:
"On the early morning of the 24th a violent outburst of gas
against nearly the whole front was varied by heavy shell fire,
and a most determined attack was delivered against our position
east of Ypres. The real attack commenced at 2.45 a.m. A
large proportion of the men were asleep, and the attack was
too sudden to give them time to put on their respirators."
These latter were hurriedly improvised after the first Ypres attack.