of prisoners, of documents captured, and of our
own observation, that the enemy has suffered heavy casualties from our
gas attacks, while the means of protection adopted by us {177} have
proved thoroughly effective" (Sir D. Haig's Dispatches).

SMOKE

Smoke can be discharged from _Artillery_ shells, Artillery or
_infantry_ mortar bombs, Infantry rifle grenades, smoke candles,
_Aircraft_ bombs, _Engineers'_ stationary generators, or the exhaust
pipe of _Tanks_. It is used to conceal movement for the purposes of
surprise or for reducing casualties, and can be so employed as to
impose night conditions on the enemy while one's own troops retain the
natural visibility; but while the weight and direction of an intended
blow may thus be hidden from the enemy a warning is given of the time
of its delivery. It is possible, however, to mystify, as well as to
surprise, the enemy by the use of smoke, and its strategical and
tactical value will ensure its adoption in Modern Warfare. In the
closing battles of the Great War "the use of smoke shells for covering
the advance of our infantry and masking the enemy's positions was
introduced and employed with increasing frequency and effect" (Sir D.
Haig's Dispatches).

{178}

OPERATION ORDERS

Combatant officers of every rank are required to issue orders of some
kind or other, and orders for operations should always be committed to
paper when circumstances permit. The object of an operation order is
to bring about a course of action in accordance with the intentions of
the commander, and with full co-operation between all units.

Operation orders of a complicated nature are unlikely to be required
from the pen of infantry officers in the junior ranks, and the rules
for drafting orders are stated in detail in the official text-books,
for the use of officers of the ranks that will be required to issue
them.

The general principles underlying orders of all kinds are that they
should be "fool proof," and it has been remarked that the writer of
orders should always remember that at least one silly ass will try to
misunderstand them. They must, therefore, be void of all ambiguity,
and while containing every essential piece of information, and omitting
everything that is clearly known already to the recipients, they should
be confined to facts, and conjecture should be avoided.

"An operation order must contain just what the recipient requires to
know and nothing more. I