225 horsepower Benz which was very popular, as were the 100
horse-power and 170 horse-power Mercedes, the last mentioned fitted to
the Aviatik biplane of 1917. The Uberursel was a copy of the Gnome and
supplied the need for rotary engines.

In Great Britain there were a number of aeroplane constructing firms
that had managed to emerge from the lean years 1912-1913 with
sufficient manufacturing plant to give a hand in making up the leeway of
construction when War broke out. Gradually the motor-car firms came
in, turning their body-building departments to plane and fuselage
construction, which enabled them to turn out the complete planes engined
and ready for the field. The coach-building trade soon joined in and
came in handy as propeller makers; big upholstering and furniture firms
and scores of concerns that had never dreamed of engaging in aeroplane
construction were busy on supplying the R.F.C. By 1915 hundreds of
different firms were building aeroplanes and parts; by 1917 the number
had increased to over 1,000, and a capital of over a million pounds for
a firm that at the outbreak of War had employed a score or so of hands
was by no means uncommon. Women and girls came into the work, more
especially in plane construction and covering and doping, though they
took their place in the engine shops and proved successful at acetylene
welding and work at the lathes. It was some time before Britain was able
to provide its own magnetos, for this key industry had been left in
the hands of the Germans up to the outbreak of War, and the 'Bosch' was
admittedly supreme--even now it has never been beaten, and can only be
equalled, being as near perfection as is possible for a magneto.

One of the great inventions of the War was the synchronisation of
engine-timing and machine gun, which rendered it possible to fire
through the blades of a propeller without damaging them, though the
growing efficiency of the aeroplane as a whole and of its armament is
a thing to marvel at on looking back and considering what was actually
accomplished. As the efficiency of the aeroplane increased, so
anti-aircraft guns and range-finding were improved. Before the War an
aeroplane travelling at full speed was reckoned perfectly safe at 4,000
feet, but, by the first month of 1915, the safe height had gone up to
9,000 feet, 7,000 feet being the limit of rifle and machine gun bullet
trajectory; the heavier guns were not sufficiently mobile to tackle
ai