In addition to the possibility of being shot
at by other aircraft, an important consideration was vulnerability from
the ground. Before the war reconnaissances were carried out at heights
varying from 2,000 to 6,000 feet, but it was generally considered that
the aeroplane was safe from fire from the ground at heights above 3,000
feet.

Serious difficulties affecting the mobility of aircraft were the means
of providing a regular supply of fuel and the selection of landing
grounds when moving camp, which had to be close enough behind the front
line as not to entail waste of time in flying out and back over friendly
territory. This was later brought home to us in a very acute form during
the Retreat from Mons.

As machines improved, increasing attention was paid to bettering their
power of reconnaissance by air photography, their value in co-operation
with artillery by wireless equipment, their offensive action by bomb
dropping and their offence and defence by armament.

The value of a correct initiative and the aeroplane's role as an
offensive weapon were fully appreciated and brought out in the Training
Manual of the Royal Flying Corps which we compiled at Farnborough, and
which was published early in 1914 by the War Office. It says:--

"It is probable that one phase of the struggle for the command of
the air will resolve itself into a series of combats between
individual aeroplanes, or pairs of aeroplanes. If the pilots of one
side can succeed in obtaining victory in a succession of such
combats, they will establish a moral ascendancy over the surviving
pilots of the enemy, and be left free to carry out their duties of
reconnaissance. The actual tactics must depend on the types of the
aeroplanes engaged, the object of the pilot being to obtain for his
passenger the free use of his own weapon while denying to the enemy
the use of his. To disable the pilot of the opposing aeroplane will
be the first object. In the case of fast reconnaissance aeroplanes
it will often be advisable to avoid fighting, in order to carry out
a mission or to deliver information; but it must be borne in mind
that this will be sometimes impossible, and that, as in every other
class of fighting, a fixed determination to attack and win will be
the surest road to victory."

Speaking generally, the evolution of the machine, as apart from the
engine, which hung behind, followed upon t