while at the same time the clouds of
smoke guide one to the point and enable the cylinder to be recovered.
This device is extensively used by the German aviators, and has proved
highly serviceable; a similar contrivance is adopted by French airmen.

There is one phase of aerial activity which remains to be demonstrated.
This is the utilisation of aerial craft by the defenders of a besieged
position such as a ring of fortifications or fortified city. The utility
of the Fourth Arm in this province has been the subject of considerable
speculation. Expert opinion maintains that the advantage in this
particular connection would rest with the besiegers. The latter would
be able to ascertain the character of the defences and the defending
gun-force, by means of the aerial scout, who would prove of inestimable
value in directing the fire of the besieging forces.

On the other hand it is maintained that an aerial fleet would be useless
to the beleaguered. In the first place the latter would experience
grave difficulties in ascertaining the positions of the attacking
and fortress-reducing artillery, inasmuch as this could be masked
effectively, and it is thought that the aerial force of the besieged
would be speedily reduced to impotence, since it would be subjected to
an effective concentrated fire from the ring of besieging anti-aircraft
guns and other weapons. In other words, the theory prevails that an
aerial fleet, no matter how efficient, would be rendered ineffective for
the simple reason that it would be the initial object of the besieger's
attack. Possibly the stem test of experience will reveal the fallacy of
these contentions as emphatically as it has disproved others. But there
is one point upon which authorities are unanimous. If the artillery of
the investing forces is exposed and readily distinguishable, the aerial
forces of the beleaguered will bring about its speedy annihilation, as
the defensive artillery will be concentrated upon that of the besiegers.

CHAPTER IX. THE AIRMAN AND ARTILLERY

There is one field in which the airman has achieved distinctive
triumphs. This is in the guidance of artillery fire. The modern battle
depends first and foremost upon the fierce effectiveness of big-gun
assault, but to ensure this reliable direction is imperative. No force
has proved so invaluable for this purpose as the man of-the-air, and
consequently this is the province in which he has been exceptionally and
succ